We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity ($|y|<$ 0.7) in Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Invariant yields of HFEs are measured for the transverse momentum range of $3.5 < p_{\rm T} < 9$ GeV/$c$ in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in $p$+$p$ collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.
Ratios of NPE (non-photonic electron) to PHE (photonic electron) as a function of $p_{\rm T}$ in 0-10% central (yellow circles) and 40-80% peripheral (green squares) Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Vertical bars represent statistical uncertainties while boxes represent systematic uncertainties. Horizontal bars indicate the bin width.
Invariant yields of electrons from decays of prompt $J/\psi$ (dot-dashed line), $\Upsilon$ (dotted line), Drell-Yan (long dash-dotted line), light vector mesons (long dashed line) and the combined HDE (hadron decayed electron) contribution (solid line), estimated utilizing experimental measurements, theoretical calculations, and PYTHIA and $\rm E_{VT}G_{EN}$ event generators, in 0-10% central Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Color bands represent systematic uncertainties.
Invariant yields of electrons from decays of prompt $J/\psi$ (dot-dashed line), $\Upsilon$ (dotted line), Drell-Yan (long dash-dotted line), light vector mesons (long dashed line) and the combined HDE (hadron decayed electron) contribution (solid line), estimated utilizing experimental measurements, theoretical calculations, and PYTHIA and $\rm E_{VT}G_{EN}$ event generators, in 40-80% central Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Color bands represent systematic uncertainties.
We report on the first measurement of charm-strange meson $D_s^{\pm}$ production at midrapidity in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV from the STAR experiment. The yield ratio between strange ($D_{s}^{\pm}$) and non-strange ($D^{0}$) open-charm mesons is presented and compared to model calculations. A significant enhancement, relative to a PYTHIA simulation of $p$+$p$ collisions, is observed in the $D_{s}^{\pm}/D^0$ yield ratio in Au+Au collisions over a large range of collision centralities. Model calculations incorporating abundant strange-quark production in the quark-gluon plasma (QGP) and coalescence hadronization qualitatively reproduce the data. The transverse-momentum integrated yield ratio of $D_{s}^{\pm}/D^0$ at midrapidity is consistent with a prediction from a statistical hadronization model with the parameters constrained by the yields of light and strange hadrons measured at the same collision energy. These results suggest that the coalescence of charm quarks with strange quarks in the QGP plays an important role in $D_{s}^{\pm}$ meson production in heavy-ion collisions.
The $KK\pi$ invariant mass distribution (Counts per 8 MeV/$c^{2}$ bin) for right-sign combinations in 0-80% Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV.
$D_s^{\pm}$ invariant yield as a function of $p_{T}$ in 0-10% centrality bin of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV. The $p_T$ bins are 1.5 < $p_T$ < 2.5 GeV/c, 2.5 < $p_T$ < 3.5 GeV/c, 3.5 < $p_T$ < 5.0 GeV/c and 5.0 < $p_T$ < 8.0 GeV/c.
$D_s^{\pm}$ invariant yield as a function of $p_{T}$ in 10-40% centrality bin of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV. The $p_T$ bins are 1.0 < $p_T$ < 2.0 GeV/c, 2.0 < $p_T$ < 2.5 GeV/c, 2.5 < $p_T$ < 3.5 GeV/c, 3.5 < $p_T$ < 5.0 GeV/c and 5.0 < $p_T$ < 8.0 GeV/c.
Global polarization of $\Xi$ and $\Omega$ hyperons has been measured for the first time in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The measurements of the $\Xi^-$ and $\bar{\Xi}^+$ hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay $\Xi\rightarrow\Lambda+\pi$, as well as by measuring the polarization of the daughter $\Lambda$-hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over $\Xi^-$ and $\bar{\Xi}^+$, is measured to be $\langle P_\Xi \rangle = 0.47\pm0.10~({\rm stat.})\pm0.23~({\rm syst.})\,\%$ for the collision centrality 20%-80%. The $\langle P_\Xi \rangle$ is found to be slightly larger than the inclusive $\Lambda$ polarization and in reasonable agreement with a multi-phase transport model (AMPT). The $\langle P_\Xi \rangle$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of $\Omega$, $\langle P_\Omega \rangle = 1.11\pm0.87~({\rm stat.})\pm1.97~({\rm syst.})\,\%$ was obtained by measuring the polarization of daughter $\Lambda$ in the decay $\Omega \rightarrow \Lambda + K$, assuming the polarization transfer factor $C_{\Omega\Lambda}=1$.
$\Xi$ and $\Omega$ global polarization in Au+Au collisions at 200 GeV. Decay parameter from PDG2020, $\alpha_{\Xi}$=-$\alpha_{\bar{\Xi}}$=-0.401, is used.
The energy dependence of $\Lambda$ and $\bar{\Lambda}$ global polarization. Note that the results from previous measurements are rescaled using updated decay parameters (PDG2020), $\alpha_{\Lambda}$=0.732 and $\alpha_{\bar{\Lambda}}$=-0.758. The original data can be found in <a href="https://www.hepdata.net/record/ins1510474">this page</a>.
Centrality dependence of $\Xi$ global poalrization in Au+Au collisions at 200 GeV. Decay parameter from PDG2020, $\alpha_{\Xi}$=-$\alpha_{\bar{\Xi}}$=-0.401, is used.
The STAR Collaboration reports measurements of the transverse single-spin asymmetry (TSSA) of inclusive $\pi^0$ at center-of-mass energies ($\sqrt s$) of 200 GeV and 500 GeV in transversely polarized proton-proton collisions in the pseudo-rapidity region 2.7 to 4.0. The results at the two different energies show a continuous increase of the TSSA with Feynman-$x$, and, when compared to previous measurements, no dependence on $\sqrt s$ from 19.4 GeV to 500 GeV is found. To investigate the underlying physics leading to this large TSSA, different topologies have been studied. $\pi^0$ with no nearby particles tend to have a higher TSSA than inclusive $\pi^0$. The TSSA for inclusive electromagnetic jets, sensitive to the Sivers effect in the initial state, is substantially smaller, but shows the same behavior as the inclusive $\pi^0$ asymmetry as a function of Feynman-$x$. To investigate final-state effects, the Collins asymmetry of $\pi^0$ inside electromagnetic jets has been measured. The Collins asymmetry is analyzed for its dependence on the $\pi^0$ momentum transverse to the jet thrust axis and its dependence on the fraction of jet energy carried by the $\pi^0$. The asymmetry was found to be small in each case for both center-of-mass energies. All the measurements are compared to QCD-based theoretical calculations for transverse-momentum-dependent parton distribution functions and fragmentation functions. Some discrepancies are found, which indicates new mechanisms might be involved.
Transverse single-spin asymmetry as a function of Feynman-x for \pi^0 production in transversely polarized proton-proton collisions at 200 GeV.
Transverse single-spin asymmetry as a function of Feynman-x for \pi^0 production in transversely polarized proton-proton collisions at 500 GeV.
average transverse momentum of the \pi^0 for each xF bin in transversely polarized proton-proton collisions at 200 GeV.
The STAR Collaboration reports a measurement of the transverse single-spin asymmetries, $A_{N}$, for neutral pions produced in polarized proton collisions with protons ($pp$), with aluminum nuclei ($p\rm{Al}$) and with gold nuclei ($p\rm{Au}$) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudo-rapidity region $2.7<\eta<3.8$. Results are presented for $\pi^0$s observed in the STAR FMS electromagnetic calorimeter in narrow Feynman x ($x_F$) and transverse momentum ($p_T$) bins, spanning the range $0.17<x_F<0.81$ and $1.7<p_{T}<6.0$ GeV/$c$. For fixed $x_F<0.47$, the asymmetries are found to rise with increasing transverse momentum. For larger $x_F$, the asymmetry flattens or falls as ${p_T}$ increases. Parametrizing the ratio $r(A) \equiv A_N(pA)/A_N(pp)=A^P$ over the kinematic range, the ratio $r(A)$ is found to depend only weakly on $A$, with ${\langle}P{\rangle} = -0.027 \pm 0.005$. No significant difference in $P$ is observed between the low-$p_T$ region, $p_T<2.5$ GeV/$c$, where gluon saturation effects may play a role, and the high-$p_T$ region, $p_T>2.5$ GeV/$c$. It is further observed that the value of $A_N$ is significantly larger for events with a large-$p_T$ isolated $\pi^0$ than for events with a non-isolated $\pi^0$ accompanied by additional jet-like fragments. The nuclear dependence $r(A)$ is similar for isolated and non-isolated $\pi^0$ events.
A_N pAl 0.17<x_F<0.19
A_N pp 0.17<x_F<0.19
A_N pAu 0.17<x_F<0.19
We report on the $W$ and $Z/\gamma^*$ differential and total cross sections as well as the $W^+$/$W^-$ and $(W^+ + W^-)$/$(Z/\gamma^*)$ cross-section ratios measured by the STAR experiment at RHIC in $p+p$ collisions at $\sqrt{s} = 500$ GeV and $510$ GeV. The cross sections and their ratios are sensitive to quark and antiquark parton distribution functions. In particular, at leading order, the $W$ cross-section ratio is sensitive to the $\bar{d}/\bar{u}$ ratio. These measurements were taken at high $Q^2 \sim M_W^2,M_Z^2$ and can serve as input into global analyses to provide constraints on the sea quark distributions. The results presented here combine three STAR data sets from 2011, 2012, and 2013, accumulating an integrated luminosity of 350 pb$^{-1}$. We also assess the expected impact that our $W^+/W^-$ cross-section ratios will have on various quark distributions, and find sensitivity to the $\bar{u}-\bar{d}$ and $\bar{d}/\bar{u}$ distributions.
Differential cross sections, $d\sigma^{fid}_{W^+}/d\eta_{e^+}$, binned in $e^+$ pseudorapidity bins, requiring that $-1 < \eta_e < 1.5$ and $25$ GeV $< E^e_{T} < 50$ GeV. The values labeled 'stat.' and 'eff.' represent the statistical uncertainty and the systematic uncertainty estimated from the efficiencies, respectively. The later is dominated by the 5\% uncertainty in the tracking efficiency, which is common to all the measurements. The value 'sys.' includes all remaining systematic uncertainties, with the exception of the luminosity. The 9\% uncertainty associated with the luminosity measurement is labeled as 'lumi'.
Differential cross sections, $d\sigma^{fid}_{W^-}/d\eta_{e^-}$, binned in $e^-$ pseudorapidity bins, requiring that $-1 < \eta_e < 1.5$ and $25$ GeV $< E^e_{T} < 50$ GeV. The values labeled ``stat.' and ``eff.' represent the statistical uncertainty and the systematic uncertainty estimated from the efficiencies, respectively. The later is dominated by the 5\% uncertainty in the tracking efficiency, which is common to all the measurements. The value ``sys.' includes all remaining systematic uncertainties, with the exception of the luminosity. The 9\% uncertainty associated with the luminosity measurement is labeled as 'lumi'.
Differential cross sections, $d\sigma^{fid}_{Z}/dy_Z$, binned in rapidity bins, requiring that $|\eta_e|<1$, $|y_Z| < 1$, $p^e_T > 15$ GeV, and $ 70$ GeV $< M_Z < 110$ GeV. The values labeled 'stat.' and 'eff.' represent the statistical uncertainty and the systematic uncertainty estimated from the efficiencies, respectively. The later is dominated by the 10\% uncertainty in the tracking efficiency, which is common to all the measurements. The value 'sys.' includes all remaining systematic uncertainties, with the exception of the luminosity. The 9\% uncertainty associated with the luminosity measurement is labeled as 'lumi'.
The Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC) was extended to energies below $\sqrt{\textit{s}_{NN}}$ = 7.7 GeV in 2015 by successful implementation of the fixed-target mode of operation in the STAR (Solenoidal Track At RHIC) experiment. In the fixed-target mode, ions circulate in one ring of the collider and interact with a stationary target at the entrance of the STAR Time Projection Chamber. The first results for Au+Au collisions at $\sqrt{\textit{s}_{NN}}$ = 4.5 GeV are presented, including directed and elliptic flow of identified hadrons, and radii from pion femtoscopy. The proton flow and pion femtoscopy results agree quantitatively with earlier measurements by Alternating Gradient Synchrotron experiments at similar energies. This validates running the STAR experiment in the fixed-target configuration. Pion directed and elliptic flow are presented for the first time at this beam energy. Pion and proton elliptic flow show behavior which hints at constituent quark scaling, but large error bars preclude reliable conclusions. The ongoing second phase of BES (BES-II) will provide fixed-target data sets with 100 times more events at each of several energies down to $\sqrt{\textit{s}_{NN}}$ = 3.0 GeV.
Centrality selection for STAR FXT sqrt(sNN) = 4.5 GeV Au+Au collisions
Rapidity dependence of directed flow, v1(y), for protons with transverse momentum 0.4 < pT < 2.0 GeV/c from events with 10-25% centrality.
Rapidity dependence of directed flow, v1(y), for negative pions with transverse momentum pT > 0.2 GeV/c and total momentum magnitude |p| < 1.6 GeV/c from events within 10-30% centrality. Here, the BBC-based Event Plane method is used. Plotted error bars are statistical only, and systematic errors are of comparable size.
We present a measurement of the first-order azimuthal anisotropy, $v_1(y)$, of deuterons from Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV recorded with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The energy dependence of the $v_1(y)$ slope, $dv_{1}/dy|_{y=0}$, for deuterons, where $y$ is the rapidity, is extracted for semi-central collisions (10-40\% centrality) and compared to that of protons. While the $v_1(y)$ slopes of protons are generally negative for $\sqrt{s_{NN}} >$ 10 GeV, those for deuterons are consistent with zero, a strong enhancement of the $v_1(y)$ slope of deuterons is seen at the lowest collision energy (the largest baryon density) at $\sqrt{s_{NN}} =$ 7.7 GeV. In addition, we report the transverse momentum dependence of $v_1$ for protons and deuterons. The experimental results are compared with transport and coalescence models.
The 1st-order event plane ($\Psi_{1}$) resolution as a function of centrality of Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV. The $\Psi_{1}$ is reconstructed with the BBC detectors and its resolution is estimated by the correlation of sub-$\Psi_{1}$ from east BBC and west BBC. Data presented later (10-40\% centrality) is indicated by the dashed-line box.
Rapidity dependene of $v_1$ for protons(open squares) in 10-40 \%Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV. The lines, dashed-dot line for proton and dashed line for deuteron, at the midrapidity ($|y| < 0.6$) are the fit with linear functions to extract the slopes. The plotted uncertainties are the statistical only
Rapidity dependene of $v_1$ for deuterons(solid circles) in 10-40 \%Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV. The lines, dashed-dot line for proton and dashed line for deuteron, at the midrapidity ($|y| < 0.6$) are the fit with linear functions to extract the slopes. The plotted uncertainties are the statistical only
We report on new measurements of inclusive J/$\psi$ polarization at mid-rapidity in p+p collisions at $\sqrt{s}$ = 200 GeV by the STAR experiment at RHIC. The polarization parameters, $\lambda_\theta$, $\lambda_\phi$, and $\lambda_{\theta\phi}$, are measured as a function of transverse momentum ($p_T$) in both the Helicity and Collins-Soper (CS) reference frames within $p_T< 10$ GeV/$C$. Except for $\lambda_\theta$ in the CS frame at the highest measured $p_T$, all three polarization parameters are consistent with 0 in both reference frames without any strong $p_T$ dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with non-relativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
The J/PSI(1S) polarization parameter $\lambda_\theta$ as a function of pT measured through dielectron channel in the HX frame.
The J/PSI(1S) polarization parameter $\lambda_\phi$ as a function of pT measured through dielectron channel in the HX frame.
The J/PSI(1S) polarization parameter $\lambda_\thetaphi$ as a function of pT measured through dielectron channel in the HX frame.
Flow harmonics ($\textit{v}_{n}$) of the Fourier expansion for the azimuthal distributions of hadrons are commonly employed to quantify the azimuthal anisotropy of particle production relative to the collision symmetry planes. While lower order Fourier coefficients ($\textit{v}_{2}$ and $\textit{v}_{3}$) are more directly related to the corresponding eccentricities of the initial state, the higher-order flow harmonics ($\textit{v}_{n>3}$) can be induced by a mode-coupled response to the lower-order anisotropies, in addition to a linear response to the same-order anisotropies. These higher-order flow harmonics and their linear and mode-coupled contributions can be used to more precisely constrain the initial conditions and the transport properties of the medium in theoretical models. The multiparticle azimuthal cumulant method is used to measure the linear and mode-coupled contributions in the higher-order anisotropic flow, the mode-coupled response coefficients, and the correlations of the event plane angles for charged particles as functions of centrality and transverse momentum in Au+Au collisions at nucleon-nucleon center-of-mass energy \roots = 200 GeV. The results are compared to similar LHC measurements as well as to several viscous hydrodynamic calculations with varying initial conditions.
3-particle integrated correlators
The integrated $v_{4}$ and $v_{5}$
The integrated $\chi_{4,22}$, $\rho_{4,22}$, $\chi_{5,23}$ and $\rho_{5,23}$
Quark interactions with topological gluon configurations can induce local chirality imbalance and parity violation in quantum chromodynamics, which can lead to the chiral magnetic effect (CME) -- an electric charge separation along the strong magnetic field in relativistic heavy-ion collisions. The CME-sensitive azimuthal correlator observable ($\Delta\gamma$) is contaminated by background arising, in part, from resonance decays coupled with elliptic anisotropy ($v_{2}$). We report here differential measurements of the correlator as a function of the pair invariant mass ($m_{\rm inv}$) in 20-50% centrality Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$= 200 GeV by the STAR experiment at RHIC. Strong resonance background contributions to $\Delta\gamma$ are observed. At large $m_{\rm inv}$ where this background is significantly reduced, the $\Delta\gamma$ value is found to be significantly smaller. An event-shape-engineering technique is deployed to determine the $v_{2}$ background shape as a function of $m_{\rm inv}$. We extract a $v_2$-independent and $m_{\rm inv}$-averaged signal $\Delta\gamma_{\rm sig}$ = (0.03 $\pm$ 0.06 $\pm$ 0.08) $\times10^{-4}$, or $(2\pm4\pm5)\%$ of the inclusive $\Delta\gamma(m_{\rm inv}>0.4$ GeV/$c^2$)$ =(1.58 \pm 0.02 \pm 0.02) \times10^{-4}$, within pion $p_{T}$ = 0.2 - 0.8~\gevc and averaged over pseudorapidity ranges of $-1 < \eta < -0.05$ and $0.05 < \eta < 1$. This represents an upper limit of $0.23\times10^{-4}$, or $15\%$ of the inclusive result, at $95\%$ confidence level for the $m_{\rm inv}$-integrated CME contribution.
The $m_{\rm inv}$ dependences of the OS and SS pion pair multiplicities in 20-50$\%$ Au+Au collisions at 200 GeV.
The $m_{\rm inv}$ dependences of the $\gamma_{OS}$, $\gamma_{SS}$ in 20-50$\%$ Au+Au collisions at 200 GeV.
$m_{\rm inv}$ dependences of the relative excess of OS over SS pion pairs in 20-50$\%$ Au+Au collisions at 200 GeV.
The STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive jet production in peripheral and central Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. Jets are reconstructed with the anti-k$_{T}$ algorithm using charged tracks with pseudorapidity $|\eta|<1.0$ and transverse momentum $0.2<p_{T,jet}^{ch}<30$ GeV/$c$, with jet resolution parameter $R$=0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with a previous coincidence measurement. This background is suppressed by requiring a high-transverse-momentum (high-$p_T$) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the $p_T$ region in which the bias is small is identified. Inclusive charged-particle jet distributions are reported in peripheral and central Au+Au collisions for $5<p_{T,jet}^{ch}<25$ GeV/$c$ and $5<p_{T,jet}^{ch}<30$ GeV/$c$, respectively. The charged-particle jet inclusive yield is suppressed for central Au+Au collisions, compared to both the peripheral Au+Au yield from this measurement and to the $pp$ yield calculated using the PYTHIA event generator. The magnitude of the suppression is consistent with that of inclusive hadron production at high $p_T$, and that of semi-inclusive recoil jet yield when expressed in terms of energy loss due to medium-induced energy transport. Comparison of inclusive charged-particle jet yields for different values of $R$ exhibits no significant evidence for medium-induced broadening of the transverse jet profile for $R<0.4$ in central Au+Au collisions. The measured distributions are consistent with theoretical model calculations that incorporate jet quenching.
Corrected inclusive charged-particle jet distributions in Au+Au collisions at 200 GeV for R=0.2, 0.3, and 0.4 in central (0-10%) Au+Au collisions for pTlead,min = 5 GeV/c. The first uncertainty is statistical (symmetric), followed by shape uncertainty (asymmetric) and correlated uncertainty (asymmetric).
Corrected inclusive charged-particle jet distributions in Au+Au collisions at 200 GeV for R=0.2, 0.3, and 0.4 in peripheral (60-80%) Au+Au collisions for pTlead,min = 5 GeV/c. The first uncertainty is statistical (symmetric), followed by shape uncertainty (asymmetric) and correlated uncertainty (asymmetric).
Corrected inclusive charged-particle jet distributions in Au+Au collisions at 200 GeV for R=0.2, 0.3, and 0.4 in central (0-10%) Au+Au collisions for pTlead,min = 7 GeV/c. The first uncertainty is statistical (symmetric), followed by shape uncertainty (asymmetric) and correlated uncertainty (asymmetric).
We report on the measurement of the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$) with the STAR detector at RHIC in proton-proton collisions at $\sqrt{s} = 200$ GeV. The charged particle pairs produced in the reaction $pp\to p^\prime+h^{+}h^{-}+p^\prime$ are reconstructed from the tracks in the central detector, while the forward-scattered protons are measured in the Roman Pot system. Differential cross sections are measured in the fiducial region, which roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range $0.04~\mbox{GeV}^2 < -t_1 , -t_2 < 0.2~\mbox{GeV}^2$, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range $|\eta|<0.7$. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of $\pi^{+}\pi^{-}$ and $K^{+}K^{-}$ pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to $\pi^{+}\pi^{-}$ production. The fiducial $\pi^+\pi^-$ cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described by the continuum production and at least three resonances, the $f_0(980)$, $f_2(1270)$ and $f_0(1500)$, with a possible small contribution from the $f_0(1370)$. Fits to the extrapolated differential cross section as a function of $t_1$ and $t_2$ enable extraction of the exponential slope parameters in several bins of the invariant mass of $\pi^+\pi^-$ pairs. These parameters are sensitive to the size of the interaction region.
Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the invariant mass of the pair. Systematic uncertainties assigned to data points are strongly correlated between bins and should be treated as allowed collective variation of all data points. There are two components of the total systematic uncertainty. The systematic uncertainty related to the experimental tools and analysis method is labeled "syst. (experimental)". The systematic uncertainty related to the integrated luminosity (fully correlated between all data points) is labeled "syst. (luminosity)". Fiducial region definition: * central state $\pi^+$, $\pi^-$ - $p_{\mathrm{T}} > 0.2~\mathrm{GeV}$ - $|\eta| < 0.7$ * intact forward-scattered beam protons $p'$ - $p_x > -0.2~\mathrm{GeV}$ - $0.2~\mathrm{GeV} < |p_{y}| < 0.4~\mathrm{GeV}$ - $(p_x+0.3~\mathrm{GeV})^2 + p_y^2 < 0.25~\mathrm{GeV}^2$
Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the invariant mass of the pair. Systematic uncertainties assigned to data points are strongly correlated between bins and should be treated as allowed collective variation of all data points. There are two components of the total systematic uncertainty. The systematic uncertainty related to the experimental tools and analysis method is labeled "syst. (experimental)". The systematic uncertainty related to the integrated luminosity (fully correlated between all data points) is labeled "syst. (luminosity)". Fiducial region definition: * central state $K^+$, $K^-$ - $p_{\mathrm{T}} > 0.3~\mathrm{GeV}$ - $min(p_{\mathrm{T}}(K^+), p_{\mathrm{T}}(K^-)) < 0.7~\mathrm{GeV}$ - $|\eta| < 0.7$ * intact forward-scattered beam protons $p'$ - $p_x > -0.2~\mathrm{GeV}$ - $0.2~\mathrm{GeV} < |p_{y}| < 0.4~\mathrm{GeV}$ - $(p_x+0.3~\mathrm{GeV})^2 + p_y^2 < 0.25~\mathrm{GeV}^2$
Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the invariant mass of the pair. Systematic uncertainties assigned to data points are strongly correlated between bins and should be treated as allowed collective variation of all data points. There are two components of the total systematic uncertainty. The systematic uncertainty related to the experimental tools and analysis method is labeled "syst. (experimental)". The systematic uncertainty related to the integrated luminosity (fully correlated between all data points) is labeled "syst. (luminosity)". Fiducial region definition: * central state $p$, $\bar{p}$ - $p_{\mathrm{T}} > 0.4~\mathrm{GeV}$ - $min(p_{\mathrm{T}}(p), p_{\mathrm{T}}(\bar{p})) < 1.1~\mathrm{GeV}$ - $|\eta| < 0.7$ * intact forward-scattered beam protons $p'$ - $p_x > -0.2~\mathrm{GeV}$ - $0.2~\mathrm{GeV} < |p_{y}| < 0.4~\mathrm{GeV}$ - $(p_x+0.3~\mathrm{GeV})^2 + p_y^2 < 0.25~\mathrm{GeV}^2$
We report results on the total and elastic cross sections in proton-proton collisions at $\sqrt{s}=200$ GeV obtained with the Roman Pot setup of the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The elastic differential cross section was measured in the squared four-momentum transfer range $0.045 \leq -t \leq 0.135$ GeV$^2$. The value of the exponential slope parameter $B$ of the elastic differential cross section $d\sigma/dt \sim e^{-Bt}$ in the measured $-t$ range was found to be $B = 14.32 \pm 0.09 (stat.)^{\scriptstyle +0.13}_{\scriptstyle -0.28} (syst.)$ GeV$^{-2}$. The total cross section $\sigma_{tot}$, obtained from extrapolation of the $d\sigma/dt$ to the optical point at $-t = 0$, is $\sigma_{tot} = 54.67 \pm 0.21 (stat.) ^{\scriptstyle +1.28}_{\scriptstyle -1.38} (syst.)$ mb. We also present the values of the elastic cross section $\sigma_{el} = 10.85 \pm 0.03 (stat.) ^{\scriptstyle +0.49}_{\scriptstyle -0.41}(syst.)$ mb, the elastic cross section integrated within the STAR $t$-range $\sigma^{det}_{el} = 4.05 \pm 0.01 (stat.) ^{\scriptstyle+0.18}_{\scriptstyle -0.17}(syst.)$ mb, and the inelastic cross section $\sigma_{inel} = 43.82 \pm 0.21 (stat.) ^{\scriptstyle +1.37}_{\scriptstyle -1.44} (syst.)$ mb. The results are compared with the world data.
The proton-proton elastic differential cross-section $d\sigma_{el}/dt$ in the t-range 0.045<|t|<0.135 $GeV^{2}$ at sqrt(s) = 200 GeV.
The B-slope of the exponential fit A*exp(-B*|t|) to the single differential proton-proton elastic cross-section in the t-range 0.045<|t|<0.135 GeV**2 at sqrt(s) = 200 GeV.
The total, elastic and inelastic cross-sections for proton-proton scattering at sqrt(s)=200 GeV, the elastic cross-section measured in the t-range 0.045<|t|<0.135 GeV^2 and the value of the differential cross-section extrapolated to |t| = 0.
In this letter, measurements of the shared momentum fraction ($z_{\rm{g}}$) and the groomed jet radius ($R_{\rm{g}}$), as defined in the SoftDrop algorihm, are reported in \pp collisions at $\sqrt{s} = 200$ GeV collected by the STAR experiment. These substructure observables are differentially measured for jets of varying resolution parameters from $R = 0.2 - 0.6$ in the transverse momentum range $15 < p_{\rm{T, jet}} < 60$ GeV$/c$. These studies show that, in the $p_{\rm{T, jet}}$ range accessible at $\sqrt{s} = 200$ GeV and with increasing jet resolution parameter and jet transverse momentum, the $z_{\rm{g}}$ distribution asymptotically converges to the DGLAP splitting kernel for a quark radiating a gluon. The groomed jet radius measurements reflect a momentum-dependent narrowing of the jet structure for jets of a given resolution parameter, i.e., the larger the $p_{\rm{T, jet}}$, the narrower the first splitting. For the first time, these fully corrected measurements are compared to Monte Carlo generators with leading order QCD matrix elements and leading log in the parton shower, and to state-of-the-art theoretical calculations at next-to-leading-log accuracy. We observe that PYTHIA 6 with parameters tuned to reproduce RHIC measurements is able to quantitatively describe data, whereas PYTHIA 8 and HERWIG 7, tuned to reproduce LHC data, are unable to provide a simultaneous description of both $z_{\rm{g}}$ and $R_{\rm{g}}$, resulting in opportunities for fine parameter tuning of these models for \pp collisions at RHIC energies. We also find that the theoretical calculations without non-perturbative corrections are able to qualitatively describe the trend in data for jets of large resolution parameters at high $p_{\rm{T, jet}}$, but fail at small jet resolution parameters and low jet transverse momenta.
The data points and the error bars represent the mean $p_{\rm{T, jet}}^{\rm{det}}$ and the width (RMS) for a given $p_{\rm{T, jet}}^{\rm{part}}$ selection $R = 0.4$.
Uncorrected $z_{g}$ for $20 < p_{\rm{T, jet}} < 25$ GeV/c, R=0.4 anti-kT jets
Uncorrected $R_{g}$ for $20 < p_{\rm{T, jet}} < 25$ GeV/c, R=0.4 anti-kT jets
The measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the Quantum Chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. We report the measurement of efficiency and centrality bin width corrected cumulant ratios ($C_{2}/C_{1}$, $C_{3}/C_{2}$) of net-$\Lambda$ distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality and rapidity. The results are for Au + Au collisions at five beam energies ($\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4 and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to Ultra-relativistic Quantum Molecular Dynamics (UrQMD) and Hadron Resonance Gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon and net-charge data, indicate $\Lambda$ freeze-out conditions similar to those of kaons. However, large deviations are found when comparing to temperatures obtained from net-proton fluctuations. The net-$\Lambda$ cumulants show a weak, but finite, dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.
Centrality dependence of single cumulants C1, of net-lambda multiplicity distributions at Au + Au collision 19.6 GeV. Values are shown with NBD, Poisson and UrQMD predictions. Npart values are from Phys. Rev. C 104, 024902 (2021) and they are little different than the values shown in the original paper.
Centrality dependence of single cumulants C1, of net-lambda multiplicity distributions at Au + Au collision 27 GeV. Values are shown with NBD, Poisson and UrQMD predictions.Npart values are from Phys. Rev. C 104, 024902 (2021) and they are little different than the values shown in the original paper.
Centrality dependence of single cumulants C1, of net-lambda multiplicity distributions at Au + Au collision 39 GeV. Values are shown with NBD, Poisson and UrQMD predictions.Npart values are from Phys. Rev. C 104, 024902 (2021) and they are little different than the values shown in the original paper.
Non-monotonic variation with collision energy ($\sqrt{s_{\rm NN}}$) of the moments of the net-baryon number distribution in heavy-ion collisions, related to the correlation length and the susceptibilities of the system, is suggested as a signature for the Quantum Chromodynamics (QCD) critical point. We report the first evidence of a non-monotonic variation in kurtosis times variance of the net-proton number (proxy for net-baryon number) distribution as a function of \rootsnn with 3.1$\sigma$ significance, for head-on (central) gold-on-gold (Au+Au) collisions measured using the STAR detector at RHIC. Data in non-central Au+Au collisions and models of heavy-ion collisions without a critical point show a monotonic variation as a function of $\sqrt{s_{\rm NN}}$.
Event-by-event net-proton multiplicity distributions for central (0-5$\%$) Au+Au collisions from $\sqrt{s_{NN}} = 7.7 - 200 GeV. The distributions are normalised to total number of events. The distributions are not corrected for proton and antiproton detection efficiency.
Cumulants of net-proton distributions in Au+Au collisions for nine energies from $\sqrt{s_{NN}} = 7.7 - 200 GeV for 0-5$\%$ and 70-80$\%$ centrality.
Cumulant ratios C3/C2 and C4/C2 of net-proton distributions in Au+Au collisions for eight energies from $\sqrt{s_{NN}} = 7.7 - 62.4 GeV for 0-5$\%$ centrality. Also given are the derivative of the polynomial fits to the C3/C2 and C4/C2 vs energy at each energy and the Skellam baselines for the ratios.
Particle production sensitive to non-factorizable and non-perturbative processes that contribute to the underlying event associated with a high transverse momentum ($p_{T}$) jet in proton+proton collisions at $\sqrt{s}$=200 GeV is studied with the STAR detector. Each event is divided into three regions based on the azimuthal angle with respect to the highest-$p_{T}$ jet direction: in the leading jet direction ("Toward"), opposite to the leading jet ("Away"), and perpendicular to the leading jet ("Transverse"). In the Transverse region, the average charged particle density is found to be between 0.4 and 0.6 and the mean transverse momentum, $\langle p_{T}\rangle$, between 0.5-0.7 GeV/$c$ for particles with $p_{T}$$>$0.2 GeV/$c$ at mid-pseudorapidity ($|\eta|$$<$1) and jet $p_{T}$$>$15 GeV/$c$. Both average particle density and $\langle p_{T}\rangle$ depend weakly on the leading jet $p_{T}$. Closer inspection of the Transverse region hints that contributions to the underlying event from initial- and final-state radiation are significantly smaller in these collisions than at the higher energies, up to 13 TeV, recorded at the LHC. Underlying event measurements associated with a high-$p_{T}$ jet will contribute to our understanding of QCD processes at hard and soft scales at RHIC energies, as well as provide constraints to modeling of underlying event dynamics.
Average charged particle multiplicity densities for Toward, Away, and Transverse regions as functions of the leading jet pT, with charged particle pT>0.2 GeV/c. The wide curves are PYTHIA 6 (STAR). The middle width curves are default PYTHIA 6 Perugia 2012 tune. The thin curves are PYTHIA 8 Monash 2013 tune. The solid curves are the Toward region. The sparse dashed curves are the Away region. The dense dashed curves are the Transverse region.
Transverse region average charged particle densities for pT>0.2 GeV/c (open symbols) and pT>0.5 GeV/c (filled symbols). Simulations are also shown as curves. The wide curves are PYTHIA 6 (STAR). The middle width curves are default PYTHIA 6 Perugia 2012 tune. The thin curves are PYTHIA 8 Monash 2013 tune.
Charged particle <pT> for Toward, Away, and Transverse regions as functions of the leading jet pT, with charged particle pT>0.2 GeV/c. Simulations are also shown as curves. The wide curves are PYTHIA 6 (STAR). The middle width curves are default PYTHIA 6 Perugia 2012 tune. The thin curves are PYTHIA 8 Monash 2013 tune. Note the three curves overlap for the Transverse region calculations.
Open heavy flavor hadrons provide unique probes of the medium produced in ultra-relativistic heavy-ion collisions. Due to their increased mass relative to light-flavor hadrons, long lifetime, and early production in hard-scattering interactions, they provide access to the full evolution of the partonic medium formed in heavy-ion collisions. This paper reports two-dimensional (2D) angular correlations between neutral $D$-mesons and unidentified charged particles produced in minimum-bias Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. $D^0$ and $\bar{D}^0$ mesons are reconstructed via their weak decay to $K^{\mp} \pi^{\pm}$ using the Heavy Flavor Tracker (HFT) in the Solenoidal Tracker at RHIC (STAR) experiment. Correlations on relative pseudorapidity and azimuth $(\Delta\eta,\Delta\phi)$ are presented for peripheral, mid-central and central collisions with $D^0$ transverse momentum from 2 to 10 GeV/$c$. Attention is focused on the 2D peaked correlation structure near the triggered $D^0$-meson, the {\em near-side} (NS) peak, which serves as a proxy for a charm-quark containing jet. The correlated NS yield of charged particles per $D^0$-meson and the 2D widths of the NS peak increase significantly from peripheral to central collisions. These results are compared with similar correlations using unidentified charged particles, consisting primarily of light-flavor hadrons, at similar trigger particle momenta. Similar per-trigger yields and widths of the NS correlation peak are observed. The present results provide additional evidence that $D^0$-mesons undergo significant interactions with the medium formed in heavy-ion collision and show, for the first time, significant centrality evolution of the NS 2D peak in the correlations of particles associated with a heavy-flavor hadron produced in these collisions.
Amplitude of the quadrupole term, A_Q, extracted from the fitting of the correlations, presented as a function of centrality.
Width of the near-side gaussian on the delPhi coordinate extracted from the fitting of the correlations, presented as a function of centrality.
Width of the near-side gaussian on the delEta coordinate extracted from the fitting of the correlations, presented as a function of centrality.
We report on the first measurement of the charmed baryon $\Lambda_c^{\pm}$ production at midrapidity ($|y|$ $<$ 1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider. The $\Lambda_c$/$D^0$ (denoting ($\Lambda_c^++\Lambda_c^-$)/($D^0+\bar{D^0}$)) yield ratio is measured to be 1.08 $\pm$ 0.16 (stat.) $\pm$ 0.26 (sys.) in the 0--20% most central Au+Au collisions for the transverse momentum ($p_T$) range 3 $<$ $p_T$ $<$ 6 GeV/$c$. This is significantly larger than the PYTHIA model calculations for $p+p$ collisions. The measured $\Lambda_c$/$D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au+Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured $\Lambda_c$/$D^0$ ratio.
The $pK\pi$ invariant mass distributions (Counts per 10 MeV/c^2 bin) for right-sign combinations in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200\,GeV for 0--20\% centrality class.
The $pK\pi$ invariant mass distributions (Counts per 10 MeV/c^2 bin) for wrong-sign combinations, scaled by 1/3, in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200\,GeV for 0--20\% centrality class.
The $pK\pi$ invariant mass distributions (Counts per 10 MeV/c^2 bin) for right-sign combinations in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200\,GeV for 10--80\% centrality class.
We report systematic measurements of bulk properties of the system created in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC).The transverse momentum spectra of $\pi^{\pm}$, $K^{\pm}$ and $p(\bar{p})$ are studied at mid-rapidity ($|y| < 0.1$) for nine centrality intervals. The centrality, transverse momentum ($p_T$),and pseudorapidity ($\eta$) dependence of inclusive charged particle elliptic flow ($v_2$), and rapidity-odd charged particles directed flow ($v_{1}$) results near mid-rapidity are also presented. These measurements are compared with the published results from Au+Au collisions at other energies, and from Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. The results at $\sqrt{s_{\mathrm{NN}}}$ = 14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. These results are important as the 14.5 GeV energy fills the gap in $\mu_B$, which is of the order of 100 MeV,between $\sqrt{s_{\mathrm{NN}}}$ =11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general.
The $p_{T}$ spectra of proton measured at midrapidity (|y|<0.1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.5 GeV. Spectra are plotted for nine centrality classes, with some spectra multiplied by a scale factor to improve clarity, as indicated in the legend
The $p_{T}$ spectra of antiproton measured at midrapidity (|y|<0.1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.5 GeV. Spectra are plotted for nine centrality classes, with some spectra multiplied by a scale factor to improve clarity, as indicatedin the legend
The $p_{T}$ spectra of $\pi^{+}$ measured at midrapidity (|y|<0.1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.5 GeV. Spectra are plotted for nine centrality classes, with some spectra multiplied by a scale factor to improve clarity, as indicatedin the legend
The two-particle angular correlation functions, $R_2$, of pions, kaons, and protons in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV were measured by the STAR experiment at RHIC. These correlations were measured for both like-sign and unlike-sign charge combinations and versus the centrality. The correlations of pions and kaons show the expected near-side ({\it i.e.}, at small relative angles) peak resulting from short-range mechanisms. The amplitudes of these short-range correlations decrease with increasing beam energy. However, the proton correlation functions exhibit strong anticorrelations in the near-side region. This behavior is observed for the first time in an A+A collision system. The observed anticorrelation is $p_{T}$-independent and decreases with increasing beam energy and centrality. The experimental results are also compared to the Monte Carlo models UrQMD, Hijing, and AMPT.
Angular correlation function R2(∆y,∆φ) of like-sign pions in Au+Au collisions at mid centrality 30%-40% and 0.2 < pT < 2.0 GeV/c at 7.7 GeV
Angular correlation function R2(∆y,∆φ) of like-sign pions in Au+Au collisions at mid centrality 30%-40% and 0.2 < pT < 2.0 GeV/c at 11.5 GeV
Angular correlation function R2(∆y,∆φ) of like-sign pions in Au+Au collisions at mid centrality 30%-40% and 0.2 < pT < 2.0 GeV/c at 14.5 GeV
High transverse momentum ($p_T$) particle production is suppressed due to parton (jet) energy loss in the hot dense medium created in relativistic heavy-ion collisions. Redistribution of energy at low-to-modest $p_T$ has been elusive to measure because of large anisotropic backgrounds. We report a data-driven method for background evaluation and subtraction, exploiting the away-side pseudorapidity gaps, to measure the jetlike correlation shape in Au+Au collisions at $\sqrt{s_{_\mathrm{NN}}}=200$ GeV with the STAR experiment. The correlation shapes, for trigger particle $p_T>3$ GeV/$c$ and various associated particle $p_T$ ranges within $0.5<p_T<10$ GeV/$c$, are consistent with Gaussians and their widths are found to increase with centrality. The results indicate jet broadening in the medium created in central heavy-ion collisions.
Distributions of the recoil momentum within 0.5<\eta<1 (Px|_{0.5}^{1}) from high-pT trigger particles of 3<pT_Trig<10 GeV/c in 50-80% peripheral collisions
Distributions of the recoil momentum within 0.5<\eta<1 (Px|_{0.5}^{1}) from high-pT trigger particles of 3<pT_Trig<10 GeV/c in 0-10% central collisions
Dihadron azimuthal correlations in close-region and far-region for 3<pT_Trig<10 GeV/c and 1<pT_Assoc<2 GeV/c in 10-30% Au+Au collisions at \sNN=200 GeV
We present STAR measurements of strange hadron ($\mathrm{K}^{0}_{\mathrm S}$, $\Lambda$, $\overline{\Lambda}$, $\Xi^-$, $\overline{\Xi}^+$, $\Omega^-$, $\overline{\Omega}^+$, and $\phi$) production at mid-rapidity ($|y| < 0.5$) in Au+Au collisions at $\sqrt{s_{_{\mathrm{NN}}}}$ = 7.7 - 39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios ($\overline{\Lambda}$/$\Lambda$, $\overline{\Xi}^+$/$\Xi^-$, $\overline{\Omega}^+$/$\Omega^-$) are presented as well, and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out ($\mu_{B}/T_{\rm ch}$ and $\mu_{S}/T_{\rm ch}$) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors ($R_{\textrm{CP}}$) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The $\mathrm{K}^{0}_{\mathrm S}$$R_{\textrm{CP}}$ shows no suppression for $p_{\rm T}$ up to 3.5 $\mathrm{GeV} / c$ at energies of 7.7 and 11.5 GeV. The $\overline{\Lambda}$/$\mathrm{K}^{0}_{\mathrm S}$ ratio also shows baryon-to-meson enhancement at intermediate $p_{\rm T}$ ($\approx$2.5 $\mathrm{GeV} / c$) in central collisions at energies above 19.6 GeV. Both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.
Data from STAR beam energy scan (Phase I) at RHIC, for mid-rapidity (|y|<0.5)
Data from STAR beam energy scan (Phase I) at RHIC, for mid-rapidity (|y|<0.5)
Data from STAR beam energy scan (Phase I) at RHIC, for mid-rapidity (|y|<0.5)
Quark interactions with topological gluon configurations can induce chirality imbalance and local parity violation in quantum chromodynamics. This can lead to electric charge separation along the strong magnetic field in relativistic heavy-ion collisions -- the chiral magnetic effect (CME). We report measurements by the STAR collaboration of a CME-sensitive observable in $p$+Au and $d$+Au collisions at 200 GeV, where the CME is not expected, using charge-dependent pair correlations relative to a third particle. We observe strong charge-dependent correlations similar to those measured in heavy-ion collisions. This bears important implications for the interpretation of the heavy-ion data.
The $\gamma_{OS}$ correlators in p+Au collisions at $\sqrt{s_{NN}}=200$ GeV at RHIC as a function of multiplicity.
The $\gamma_{SS}$ correlators in p+Au collisions at $\sqrt{s_{NN}}=200$ GeV at RHIC as a function of multiplicity.
The $\gamma_{OS}$ correlators in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV at RHIC as a function of multiplicity.
We report the first measurement of the inclusive jet and the dijet longitudinal double-spin asymmetries, $A_{LL}$, at midrapidity in polarized $pp$ collisions at a center-of-mass energy $\sqrt{s} = 510$ GeV. The inclusive jet $A_{LL}$ measurement is sensitive to the gluon helicity distribution down to a gluon momentum fraction of $x\approx 0.015$, while the dijet measurements, separated into four jet-pair topologies, provide constraints on the $x$ dependence of the gluon polarization. Both results are consistent with previous measurements made at $\sqrt{s}= 200$ GeV in the overlapping kinematic region, $x > 0.05$, and show good agreement with predictions from recent next-to-leading order global analyses.
Fractions of the next-to-leading-order cross section for inclusive jet production arising from quark-quark, quark-gluon and gluon-gluon scattering in pp collisions (200GeV)
Fractions of the next-to-leading-order cross section for inclusive jet production arising from quark-quark, quark-gluon and gluon-gluon scattering in pp collisions (500GeV)
The upper panel shows the jet yield vs detector jet pT in data and simulation for each of the three trigger categories. The lower three panels show the relative differences between data and simulation (JP0)
$J/\psi$ suppression has long been considered a sensitive signature of the formation of the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. In this letter, we present the first measurement of inclusive $J/\psi$ production at mid-rapidity through the dimuon decay channel in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR experiment. These measurements became possible after the installation of the Muon Telescope Detector was completed in 2014. The $J/\psi$ yields are measured in a wide transverse momentum ($p_{\rm{T}}$) range of 0.15 GeV/$c$ to 12 GeV/$c$ from central to peripheral collisions. They extend the kinematic reach of previous measurements at RHIC with improved precision. In the 0-10% most central collisions, the $J/\psi$ yield is suppressed by a factor of approximately 3 for $p_{\rm{T}}>5$ GeV/$c$ relative to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The $J/\psi$ nuclear modification factor displays little dependence on $p_{\rm{T}}$ in all centrality bins. Model calculations can qualitatively describe the data, providing further evidence for the color-screening effect experienced by $J/\psi$ mesons in the QGP.
Invariant yield of inclusive J/PSI(1S) times branching ratio to the dimuon decay in 0-80% Au+Au collisions at 200 GeV
Invariant yield of inclusive J/PSI(1S) times branching ratio to the dimuon decay in 0-20% Au+Au collisions at 200 GeV
Invariant yield of inclusive J/PSI(1S) times branching ratio to the dimuon decay in 20-40% Au+Au collisions at 200 GeV
The $\Lambda$ ($\bar{\Lambda}$) hyperon polarization along the beam direction has been measured for the first time in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The polarization dependence on the hyperons' emission angle relative to the second-order event plane exhibits a sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum ($p_T$) dependence at $p_T>1$ GeV/$c$. The magnitude of the signal is about five times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, blast-wave model calculations reproduce the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the signal once the model is required to reproduce the azimuthal dependence of the Gaussian source radii measured via the Hanbury-Brown and Twiss intensity interferometry technique.
$\langle \cos\theta_p* \rangle$ of $\Lambda$ and $\bar{\Lambda}$ hyperons as a function of azimuthal angle $\phi$ relative to the second-order event plane $\Psi_2$ for 20%–60% centrality bin in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
The second Fourier sine coefficient $\langle P_Z \sin(2\phi-2\Psi_2) \rangle$ of the polarization of $\Lambda$ and $\bar{\Lambda}$ along the beam direction as a function of the collision centrality in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
The second Fourier sine coefficient $\langle P_Z \sin(2\phi-2\Psi_2) \rangle$ of the polarization of $\Lambda$ and $\bar{\Lambda}$ along the beam direction as a function of the collision centrality in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. Results updated with $\alpha_{\Lambda} = -\alpha_{\bar{\Lambda}} = 0.732$.
We present measurements of the differential production cross sections of the inclusive $J/\psi$ meson as a function of transverse momentum ($p_{T}^{J/\psi}$) using the $\mu^{+}\mu^{-}$ and $e^{+}e^{-}$ decay channels in proton+proton collisions at center-of-mass energies of 510 and 500 GeV, respectively, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The measurement from the $\mu^{+}\mu^{-}$ channel is for 0 $< p_{T}^{J/\psi} <$ 9 GeV/$c$ and rapidity range $|y^{J/\psi}| < $ 0.4, and that from the $e^{+}e^{-}$ channel is for 4 $< p_{T}^{J/\psi} <$ 20 GeV/$c$ and $|y^{J/\psi}| < $ 1.0. The $\psi(2S)$ to $J/\psi$ ratio is also measured for 4 $< p_{T}^{\rm meson} <$ 12 GeV/$c$ through the $e^{+}e^{-}$ decay channel. Model calculations, which incorporate different approaches toward the $J/\psi$ production mechanism, are compared with experimental results and show reasonable agreement within uncertainties. A more discriminating comparison to theoretical models at low $p_T$ can be performed in the future, if the calculations are carried out within our fiducial volume, eliminating the uncertainty due to the $J/\psi$ polarization.
'fiducial cross sections multiplied by the branching ratio as a function of $J/\Psi$ $p_T$'
'full cross sections multiplied by the branching ratio as a function of $J/\Psi$ $p_T$ '
'fiducial cross sections multiplied by the branching ratio as a function of $J/\Psi$ $p_T$ '
We report the first measurement of rapidity-odd directed flow ($v_{1}$) for $D^{0}$ and $\overline{D^{0}}$ mesons at mid-rapidity ($|y| < 0.8$) in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200\,GeV using the STAR detector at the Relativistic Heavy Ion Collider. In 10--80\% Au+Au collisions, the slope of the $v_{1}$ rapidity dependence ($dv_{1}/dy$), averaged over $D^{0}$ and $\overline{D^{0}}$ mesons, is -0.080 $\pm$ 0.017 (stat.) $\pm$ 0.016 (syst.) for transverse momentum $p_{\rm T}$ above 1.5~GeV/$c$. The absolute value of $D^0$-meson $dv_1/dy$ is about 25 times larger than that for charged kaons, with 3.4$\sigma$ significance. These data give a unique insight into the initial tilt of the produced matter, and offer constraints on the geometric and transport parameters of the hot QCD medium created in relativistic heavy-ion collisions.
Directed flow $v_1$ as a function of rapidity for $D^0$ and $\bar{D^0}$ mesons at $p_T>1.5$ GeV/c for 10–80% centrality Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
Directed flow $\langle v_1 \rangle$ for the combined samples of $D^0$ and $\bar{D^0}$ mesons at $p_T>1.5$ GeV/c for 10–80% centrality Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
Difference in $v_1(y)$ $(\Delta v_1)$ between $D^0$ and $\bar{D^0}$ mesons at $p_T>1.5$ GeV/c for 10–80% centrality Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
We report on the first measurements of J/$\psi$ production at very low transverse momentum ($p_{T} <$ 0.2 GeV/c) in hadronic Au+Au collisions at $\sqrt{s_{\rm{NN}}} =$ 200 GeV and U+U collisions at $\sqrt{s_{\rm{NN}}} =$ 193 GeV. Remarkably, the inferred nuclear modification factor of J/$\psi$ at mid-rapidity in Au+Au (U+U) collisions reaches about 24 (52) for $p_{T} <$ 0.05 GeV/c in the 60-80$\%$ collision centrality class. This noteworthy enhancement cannot be explained by hadronic production accompanied by cold and hot medium effects. In addition, the $dN/dt$ distribution of J/$\psi$ for the very low $p_{T}$ range is presented for the first time. The distribution is consistent with that expected from the Au nucleus and shows a hint of interference. Comparison of the measurements to theoretical calculations of coherent production shows that the excess yield can be described reasonably well and reveals a partial disruption of coherent production in semi-central collisions, perhaps due to the violent hadronic interactions. Incorporating theoretical calculations, the results strongly suggest that the dramatic enhancement of J/$\psi$ yield observed at extremely low $p_{T}$ originates from coherent photon-nucleus interactions. In particular, coherently produced J/$\psi$'s in violent hadronic collisions may provide a novel probe of the quark-gluon-plasma.
'$J/\Psi$ invariant yields for Au+Au collisions 200 GeV as a function of $p_T$'
'$J/\Psi$ invariant yields for U+U collisions 193 GeV as a function of $p_T$'
'$J/\Psi$ $R_{AA}$ for Au+Au collisions 200 GeV as a function of $p_T$'
According to the CPT theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. This hypernucleus is the lightest one yet discovered and consists of a proton, a neutron, and a $\Lambda$ hyperon. With data recorded by the STAR detector{\cite{TPC,HFT,TOF}} at the Relativistic Heavy Ion Collider, we measure the $\Lambda$ hyperon binding energy $B_{\Lambda}$ for the hypertriton, and find that it differs from the widely used value{\cite{B_1973}} and from predictions{\cite{2019_weak, 1995_weak, 2002_weak, 2014_weak}}, where the hypertriton is treated as a weakly bound system. Our results place stringent constraints on the hyperon-nucleon interaction{\cite{Hammer2002, STAR-antiH3L}}, and have implications for understanding neutron star interiors, where strange matter may be present{\cite{Chatterjee2016}}. A precise comparison of the masses of the hypertriton and the antihypertriton allows us to test CPT symmetry in a nucleus with strangeness for the first time, and we observe no deviation from the expected exact symmetry.
Measurements of relative mass-to-charge ratio differences between nuclei and antinuclei (d and antid)
Measurements of relative mass-to-charge ratio differences between nuclei and antinuclei (He and antiHe)
Measurements of relative mass-to-charge ratio differences between nuclei and antinuclei (hypertriton and antihypertriton)
We report the energy dependence of mid-rapidity (anti-)deuteron production in Au+Au collisions at $\sqrt{s_\text{NN}} =\ $7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by the STAR experiment at RHIC. The yield of deuterons is found to be well described by the thermal model. The collision energy, centrality, and transverse momentum dependence of the coalescence parameter $B_2$ are discussed. We find that the values of $B_2$ for anti-deuterons are systematically lower than those for deuterons, indicating that the correlation volume of anti-baryons is larger than that of baryons at $\sqrt{s_\text{NN}}$ from 19.6 to 39 GeV. In addition, values of $B_2$ are found to vary with collision energy and show a broad minimum around $\sqrt{s_\text{NN}}=\ $20 to 40 GeV, which might imply a change of the equation of state of the medium in these collisions.
'transverse momentum spectra for deuterons in Au+Au collisions'
'transverse momentum spectra for deuterons in Au+Au collisions'
'transverse momentum spectra for deuterons in Au+Au collisions'
We report the first measurements of a complete second-order cumulant matrix of net-charge, net-proton, and net-kaon multiplicity distributions for the first phase of the beam energy scan program at RHIC. This includes the centrality and, for the first time, the pseudorapidity window dependence of both diagonal and off-diagonal cumulants in Au+Au collisions at \sNN~= 7.7-200 GeV. Within the available acceptance of $|\eta|<0.5$, the cumulants grow linearly with the pseudorapidity window. Relative to the corresponding measurements in peripheral collisions, the ratio of off-diagonal over diagonal cumulants in central collisions indicates an excess correlation between net-charge and net-kaon, as well as between net-charge and net-proton. The strength of such excess correlation increases with the collision energy. The correlation between net-proton and net-kaon multiplicity distributions is observed to be negative at \sNN~= 200 GeV and change to positive at the lowest collision energy. Model calculations based on non-thermal (UrQMD) and thermal (HRG) production of hadrons cannot explain the data. These measurements will help map the QCD phase diagram, constrain hadron resonance gas model calculations, and provide new insights on the energy dependence of baryon-strangeness correlations. An erratum has been added to address the issue of self-correlation in the previously considered efficiency correction for off-diagonal cumulant measurement. Previously considered unidentified (net-)charge correlation results ($\sigma^{11}_{Q,p}$ and $\sigma^{11}_{Q,k})$ are now replaced with identified (net-)charge correlation ($\sigma^{11}_{Q^{PID},p}$ and $\sigma^{11}_{Q^{PID},k}$)
The dependence of efficiency corrected second-order diagonal and off-diagonal cumulants on the width of the η-window. The filled and open circles represent 0-5% and 70-80% central collisions respectively. The shaded band represents the systematic uncertainty. The statistical uncertainties are within the marker size and solid lines are UrQMD calculations.
The dependence of efficiency corrected second-order diagonal and off-diagonal cumulants on the width of the η-window. The filled and open circles represent 0-5% and 70-80% central collisions respectively. The shaded band represents the systematic uncertainty. The statistical uncertainties are within the marker size and solid lines are UrQMD calculations.
Centrality dependence of efficiency corrected second-order diagonal cumulants of net-proton, net-kaon and net-pion (top to bottom) of the multiplicity distributions for Au+Au collisions at GeV (left to right) within kinematic range of |η| < 0.5 and 0.4 < pT < 1.6 GeV/c. The boxes represent the systematic error. The statistical error bars are within the marker size. The dashed lines represent scaling predicted by central limit theorem and the solid lines are UrQMD calculations.
The first ($v_1^{\text{even}}$), second ($v_2$) and third ($v_3$) harmonic coefficients of the azimuthal particle distribution at mid-rapidity, are extracted for charged hadrons and studied as a function of transverse momentum ($p_T$) and mean charged particle multiplicity density $\langle \mathrm{N_{ch}} \rangle$ in U+U ($\roots =193$~GeV), Au+Au, Cu+Au, Cu+Cu, $d$+Au and $p$+Au collisions at $\roots = 200$~GeV with the STAR Detector. For the same $\langle \mathrm{N_{ch}} \rangle$, the $v_1^{\text{even}}$ and $v_3$ coefficients are observed to be independent of collision system, while $v_2$ exhibits such a scaling only when normalized by the initial-state eccentricity ($\varepsilon_2$). The data also show that $\ln(v_2/\varepsilon_2)$ scales linearly with $\langle \mathrm{N_{ch}} \rangle^{-1/3}$. These measurements provide insight into initial-geometry fluctuations and the role of viscous hydrodynamic attenuation on $v_n$ from small to large collision systems.
Two-particle azimuthal correlation functions for various systems for $<Nch>=21\pm3$
Second-order cumulant $c_{2}${4}($\times10^{6})$ vs $<N_{ch}>$ for various systems
$v_{1}^{fluc}$ as a function of $p_{T}(GeV/c)$ for various systems for $<Nch>=21\pm3$
We present two-particle $p_{\rm t}$ correlations as a function of event centrality for Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV at the Relativistic Heavy Ion Collider using the STAR detector. These results are compared to previous measurements from CERES at the Super Proton Synchrotron and from ALICE at the Large Hadron Collider. The data are compared with UrQMD model calculations and with a model based on a Boltzmann-Langevin approach incorporating effects from thermalization. The relative dynamical correlations for Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV show a power law dependence on the number of participant nucleons and agree with the results for Pb+Pb collisions at $\sqrt{s_{\rm NN}} = 2.76~ {\rm TeV}$ from ALICE. As the collision energy is lowered from $\sqrt{s_{\rm NN}}$ = 200 GeV to 7.7 GeV, the centrality dependence of the relative dynamical correlations departs from the power law behavior observed at the higher collision energies. In central collisions, the relative dynamical correlations increase with collision energy up to $\sqrt{s_{\rm NN}}$ = 200 GeV in contrast to previous measurements that showed little dependence on the collision energy.
'The relative dynamical correlation as a function of $N_{part}$'
'The relative dynamical correlation as a function of $N_{part}$'
'The relative dynamical correlation as a function of $N_{part}$'
We report a new measurement of $D^0$-meson production at mid-rapidity ($|y|$\,$<$\,1) in Au+Au collisions at ${\sqrt{s_{\rm NN}} = \rm{200\,GeV}}$ utilizing the Heavy Flavor Tracker, a high resolution silicon detector at the STAR experiment. Invariant yields of $D^0$-mesons with transverse momentum $p_{T}$ $\lesssim 9$\,GeV/$c$ are reported in various centrality bins (0--10\%, 10--20\%, 20--40\%, 40--60\% and 60--80\%). Blast-Wave thermal models are used to fit the $D^0$-meson $p_{T}$ spectra to study $D^0$ hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons ($\pi,K$ and $p$), but comparable to that of hadrons containing multiple strange quarks ($\phi,\Xi^-$), indicating that $D^0$ mesons kinetically decouple from the system earlier than light hadrons. The calculated $D^0$ nuclear modification factors re-affirm that charm quarks suffer large amount of energy loss in the medium, similar to those of light quarks for $p_{T}$\,$>$\,4\,GeV/$c$ in central 0--10\% Au+Au collisions. At low $p_{T}$, the nuclear modification factors show a characteristic structure qualitatively consistent with the expectation from model predictions that charm quarks gain sizable collective motion during the medium evolution. The improved measurements are expected to offer new constraints to model calculations and help gain further insights into the hot and dense medium created in these collisions.
$D^0$ (in terms of (D0 +D0)/2)) invariant yield at mid-rapidity ($|y| < 1$) vs transverse momentum for different centrality classes. Error bars indicate statistical uncertainties and brackets depict systematic uncertainties. Global systematic uncertainties in B.R. are not plotted. Solid and dashed lines depict Levy function fits.
$D^0$ (in terms of (D0 +D0)/2)) spectra in pp collisions. Note, the $\sigma_{NSD}$ = 30 $m$b for p+p was used in the calculations.
Integrated $D^0$ cross section per nucleon-nucleon collision at mid-rapidity for $p_T >0$ (a) and $p_T >4$ GeV/c (b) as a function of centrality $N_{part}$. The statistical and systematic uncertainties are shown as error bars and brackets on the data points. The green boxes on the data points depict the overall normalization uncertainties in p+p and Au+Au data respectively.
We report new STAR measurements of the single-spin asymmetries $A_L$ for $W^+$ and $W^-$ bosons produced in polarized proton--proton collisions at $\sqrt{s}$ = 510 GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250 pb$^{-1}$. The results are combined with previous results obtained with 86 pb$^{-1}$. A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton--proton data suggests a difference between the $\bar{u}$ and $\bar{d}$ quark helicity distributions for $0.05 < x < 0.25$. In addition, we report new results for the double-spin asymmetries $A_{LL}$ for $W^\pm$, as well as $A_L$ for $Z/\gamma^*$ production and subsequent decay into electron--positron pairs.
Distribution of the product of Q, the TPC recon-structed charge-sign, and $E_T/p_T$ in the BEMC region.
Distribution of the product of Q, the TPC recon-structed charge-sign, and $E_T/p_T$ in the EEMC region.
$E_T^e$ distributions of electron candidate events, background contributions, and sum of backgrounds and $W \rightarrow e\nu$ MC signal in the BEMC region for $-1.1 < \eta_e < -0.5$.
The transverse spin transfer from polarized protons to $\Lambda$ and $\bar{\Lambda}$ hyperons is expected to provide sensitivity to the transversity distribution of the nucleon and to the transversely polarized fragmentation functions. We report the first measurement of the transverse spin transfer to $\Lambda$ and $\bar{\Lambda}$ along the polarization direction of the fragmenting quark, $D_\mathrm{TT}$, in transversely polarized proton-proton collisions at $\sqrt{s}=200\,\mathrm{GeV}$ with the STAR detector at RHIC. The data correspond to an integrated luminosity of $18\,\mathrm{pb}^{-1}$ and cover the pseudorapidity range $\left|\eta\right| < 1.2$ and transverse momenta $p_{\mathrm{T}}$ up to $8\,\mathrm{GeV}/c$. The dependence on $p_\mathrm{T}$ and $\eta$ are presented. The $D_\mathrm{TT}$ results are found to be comparable with a model prediction, and are also consistent with zero within uncertainties.
'Transverse spin transfer of $\Lambda$ in transversely polarized proton-proton collisions at 200 GeV.'
'Transverse spin transfer of $\bar{\Lambda}$ in transversely polarized proton-proton collisions at 200 GeV.'
'spin asymmetry $\delta_{TT}$ for the control sample of $K_S^0$ meson.'
The longitudinal spin transfer $D_{LL}$ to $\Lambda$ and $\bar{\Lambda}$ hyperons produced in high-energy polarized proton--proton collisions is expected to be sensitive to the helicity distribution functions of strange quarks and anti-quarks of the proton, and to longitudinally polarized fragmentation functions. We report an improved measurement of $D_{LL}$ from data obtained at a center-of-mass energy of $\sqrt{s}$ = 200 GeV with the STAR detector at RHIC. The data have an approximately twelve times larger figure-of-merit than prior results and cover $|\eta|<$ 1.2 in pseudo-rapidity with transverse momenta $p_T$ up to 6 GeV/c. In the forward scattering hemisphere at largest $p_T$, the longitudinal spin transfer is found to be $D_{LL}$ = -0.036 $\pm$ 0.048 (stat) $\pm$ 0.013(sys) for $\Lambda$ hyperons and $D_{LL}$ = 0.032 $\pm$ 0.043\,(stat) $\pm$ 0.013\,(sys) for $\bar{\Lambda}$ anti-hyperons. The dependences on $\eta$ and $p_T$ are presented and compared with model evaluations.
The invariant mass distribution for $\Lambda$ and $\bar{\Lambda}$ candidates with 3 < p_T < $ 4 GeV/c in this analysis
The raw spin transfer $D _{LL}^{raw}$ versus cos$\theta^*$ for a) $\Lambda$ and b) $\bar{\Lambda}$ hyperons and c) the spin asymmetry $\delta_{LL}$ for the control sample of $K_S^0$ mesons versus cos$\theta^*$ for $3<p_T<4$ GeV/c for JP1 triggered sample.
The raw spin transfer $D _{LL}^{raw}$ versus cos$\theta^*$ for a) $\Lambda$ and b) $\bar{\Lambda}$ hyperons and c) the spin asymmetry $\delta_{LL}$ for the control sample of $K_S^0$ mesons versus cos$\theta^*$ for $3<p_T<4$ GeV/c for JP1 triggered sample. Results updated with $\alpha_{\Lambda (\bar{\Lambda})} = 0.732$.
We present the first measurement of the proton-$\Omega$ correlation function in heavy-ion collisions for central (0-40$\%$) and peripheral (40-80$\%$) Au+Au collisions at \sqrtsNN\,\,=200 GeV by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Predictions for the ratio of peripheral collisions to central collisions for the proton-$\Omega$ correlation function are sensitive to the presence of a nucleon-$\Omega$ bound state. These predictions are based on the proton-$\Omega$ interaction extracted from (2+1)-flavor lattice QCD calculations at the physical point. The measured ratio of proton-$\Omega$ correlation function from peripheral (small system) to central (large system) collisions is less than unity for relative momentum smaller than 40 MeV/c. Comparison of our measured correlation ratio with the theoretical calculation slightly favors a proton-$\Omega$ bound system with a binding energy of $\sim$ 27~MeV.
Measured correlation function (C($k^{*}$)) for proton-$\Omega$ and antiproton-$\bar{\Omega}$ (P$\Omega$ + $\bar{P}$$\bar{\Omega}$) for (0-40)$\%$ and (40-80$\%$) Au+Au collisons at $\sqrt{s}_{NN}$ = 200 GeV. The errors are statistical and systematic.
Ratio of small system (40-80$\%$) to large system (0-40$\%$) for proton-$\Omega$ and antiproton-$\bar{\Omega}$ (P$\Omega$ + $\bar{P}$$\Omega$). The errors are statistical and symmetric.
We report first measurements of $e^{+}e^{-}$ pair production in the mass region 0.4 $
The centrality dependence of e+e− invariant mass spectra within the STAR acceptance from Au+Au collisions and U+U collisions for pair pT < 0.15 GeV/c. The vertical bars on data points depict the statistical uncertainties, while the systematic uncertainties are shown as gray boxes. The hadronic cocktail yields from U+U collisions are ∼5%–12% higher than those from Au+Au collisions in given centrality bins; thus only cocktails for Au+Au collisions are shown here as solid lines, with shaded bands representing the systematic uncertainties for clarity.
The centrality dependence of e+e− invariant mass spectra within the STAR acceptance from Au+Au collisions and U+U collisions for pair pT < 0.15 GeV/c. The vertical bars on data points depict the statistical uncertainties, while the systematic uncertainties are shown as gray boxes. The hadronic cocktail yields from U+U collisions are ∼5%–12% higher than those from Au+Au collisions in given centrality bins; thus only cocktails for Au+Au collisions are shown here as solid lines, with shaded bands representing the systematic uncertainties for clarity.
The centrality dependence of e+e− invariant mass spectra within the STAR acceptance from Au+Au collisions and U+U collisions for pair pT < 0.15 GeV/c. The vertical bars on data points depict the statistical uncertainties, while the systematic uncertainties are shown as gray boxes. The hadronic cocktail yields from U+U collisions are ∼5%–12% higher than those from Au+Au collisions in given centrality bins; thus only cocktails for Au+Au collisions are shown here as solid lines, with shaded bands representing the systematic uncertainties for clarity.
The STAR Collaboration reports measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for neutral pions produced at forward directions in polarized proton-proton collisions, at a center-of-mass energy of $510$ GeV. Results are given for transverse momenta in the range $2
Longitudinal Double-Spin Asymmetry, $A_{LL}$ vs $\pi^0$ transverse momentum in polarized pp collisions at $\sqrt{s}$ = 510 GeV. $\pm 6.7\%$ polarization scale uncertainty not shown.
Longitudinal Double-Spin Asymmetry, $A_{LL}$ vs $\pi^0$ transverse momentum in polarized pp collisions at $\sqrt{s}$ = 510 GeV. $\pm 6.7\%$ polarization scale uncertainty not shown.
We present the first measurements of the longitudinal double-spin asymmetry $A_{LL}$ for dijets with at least one jet reconstructed within the pseudorapidity range $0.8 < \eta < 1.8$. The dijets were measured in polarized $pp$ collisions at a center-of-mass energy $\sqrt{s}$ = 200 GeV. Values for $A_{LL}$ are determined for several distinct event topologies, defined by the jet pseudorapidities, and span a range of parton momentum fraction $x$ down to $x \sim$ 0.01. The measured asymmetries are found to be consistent with the predictions of global analyses that incorporate the results of previous RHIC measurements. They will provide new constraints on $\Delta g(x)$ in this poorly constrained region when included in future global analyses.
Data/simulation comparisons of the relative jet yields as functions of Barrel+endcap jet pseudorapidity
Data/simulation comparisons of the relative jet yields as functions of Barrel+endcap jet azimuthal angle
Data/simulation comparisons of the relative jet yields as functions of jet transverse momentum for the barrel
Global polarization of $\Lambda$ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV, with no significant difference between $\Lambda$ and $\bar{\Lambda}$. These new results reveal the collision energy dependence of the global polarization together with the results previously observed at $\sqrt{s_{_{NN}}}$ = 7.7 -- 62.4 GeV and indicate noticeable vorticity of the medium created in non-central heavy-ion collisions at the highest RHIC collision energy. The signal is in rough quantitative agreement with the theoretical predictions from a hydrodynamic model and from the AMPT (A Multi-Phase Transport) model. The polarization is larger in more peripheral collisions, and depends weakly on the hyperon's transverse momentum and pseudorapidity $\eta^H$ within $|\eta^H|<1$. An indication of the polarization dependence on the event-by-event charge asymmetry is observed at the $2\sigma$ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.
Global polarization of $\Lambda$ and $\bar{\Lambda}$ as a function of the collision energy $\sqrt{s_{_{NN}}}$ for 20-50% centrality Au+Au collisions. Thin lines show calculations from a 3+1D cascade + viscous hydrodynamic model (UrQMD+vHLLE) and bold lines show the AMPT model calculations. In the case of each model, primary $\Lambda$ with and without the feed-down effect are indicated by dashed and solid lines, respectively. Open boxes and vertical lines show systematic and statistical uncertainties, respectively. Note that the data points at 200 GeV and for $\bar{\Lambda}$ are slightly horizontally shifted for visibility.
$\Lambda$ ($\bar\Lambda$) polarization as a function of the collision centrality in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Open boxes and vertical lines show systematic and statistical uncertainties. The data points for Λ are slightly shifted for visibility.
Polarization of $\Lambda$ and $\bar\Lambda$ as a function of $p_{T}$ for the $20\%–60\%$ centrality bin in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Open boxes and vertical lines show systematic and statistical uncertainties, respectively. Hydrodynamic model calculations for Λ with two different initial conditions (IC) are compared. Note that the data points for Λ are slightly shifted for visibility.
We present a measurement of inclusive $J/\psi$ production at mid-rapidity ($|y|<1$) in $p+p$ collisions at a center-of-mass energy of $\sqrt{s}$ = 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The differential production cross section for $J/\psi$ as a function of transverse momentum ($p_T$) for $0
Top$:$ J/$\psi$ cross section times branching ratio as a function of pT in p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV. Solid circles are from this analysis for |y| < 1; open circles and blue squares are the published results for |y| < 1 from STAR; triangles are the published results for |y| < 0.35 from PHENIX. Bars and boxes are statistical and systematic uncertainties, respectively. The curves are CEM (green), NLO NRQCD A (orange) [4], CGC + NRQCD (blue) , and NLO NRQCD B (magenta) theoretical calculations, respectively. Bottom$:$ ratios of these results with respect to the central value from this analysis.
The corrected $n_{ch}$ distributions at mid-rapidity (|$\eta$| < 1) for MB events (open circles) and J/$\psi$ events with J/$\psi$ $p_{T}$ greater than 0 (purple circles), 1.5 (blue squares), and 4 GeV/c (red triangles) in p+p collisions at $\sqrt{s}$ = 200 GeV. The fit function is a negative binomial function. Bars and boxes are statistical and systematic uncertainties, respectively.
The multiplicity dependence of J/$\psi$ production in p+p collisions at $\sqrt{s}$ = 200 GeV. Purple circles, blue squares, and red triangles represent the results for J/$\psi$ with $p_{T}$ greater than 0, 1.5, and 4 GeV/c, respectively. Bars and open boxes are statistical and systematic uncertainties, respectively. The ALICE result is shown in the left panel. The purple, blue and red bands in the middle panel are generated from PYTHIA8 for J/$\psi$ with $p_{T}$ greater than 0, 1.5, and 4 GeV/c, respectively. The blue and red bands in the right panel are from EPOS3 model calculations for D$^{0}$ with 2 < $p_{T}$ < 4 and 4 < $p_{T}$ < 8 GeV/c, respectively, while the green curve is from the Percolation model for J/$\psi$ with $p_{T}$ > 0 GeV/c.
New measurements of directed flow for charged hadrons, characterized by the Fourier coefficient \vone, are presented for transverse momenta $\mathrm{p_T}$, and centrality intervals in Au+Au collisions recorded by the STAR experiment for the center-of-mass energy range $\mathrm{\sqrt{s_{_{NN}}}} = 7.7 - 200$ GeV. The measurements underscore the importance of momentum conservation and the characteristic dependencies on $\mathrm{\sqrt{s_{_{NN}}}}$, centrality and $\mathrm{p_T}$ are consistent with the expectations of geometric fluctuations generated in the initial stages of the collision, acting in concert with a hydrodynamic-like expansion. The centrality and $\mathrm{p_T}$ dependencies of $\mathrm{v^{even}_{1}}$, as well as an observed similarity between its excitation function and that for $\mathrm{v_3}$, could serve as constraints for initial-state models. The $\mathrm{v^{even}_{1}}$ excitation function could also provide an important supplement to the flow measurements employed for precision extraction of the temperature dependence of the specific shear viscosity.
$v_{11}$ vs. $p_{T}^{b}$ for several selections of $p_{T}^{a}$ for 0-5 central Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV. The curve shows the result of the simultaneous fit.
Extracted values of $v^{even}_{1}$ vs. $p_{T}$ for 0-10 central Au+Au collisions for several values of $\sqrt{s_{_{NN}}}$ as indicated; the $v^{even}_{1}$ values are obtained via fits. The curve in panel (a) shows the result from a viscous hydrodynamically based predictions.
(a) Centrality dependence of $v^{even}_{1}$ for $0.4 \lt p_{T} \lt 0.7$ GeV/c for Au+Au collisions at $\sqrt{s_{_{NN}}} = 200, 39$ and $19.6$ GeV; (b) $K$ vs. $\langle N_{ch} \rangle^{-1}$ for the $v^{even}_{1}$ values shown in (a). The $\langle N_{ch} \rangle$ values correspond to the centrality intervals indicated in panel (a).
Flow harmonics ($v_n$) in the Fourier expansion of the azimuthal distribution of particles are widely used to quantify the anisotropy in particle emission in high-energy heavy-ion collisions. The symmetric cumulants, $SC(m,n)$, are used to measure the correlations between different orders of flow harmonics. These correlations are used to constrain the initial conditions and the transport properties of the medium in theoretical models. In this Letter, we present the first measurements of the four-particle symmetric cumulants in Au+Au collisions at $\sqrt{s_{NN}}$ = 39 and 200 GeV from data collected by the STAR experiment at RHIC. We observe that $v_{2}$ and $v_{3}$ are anti-correlated in all centrality intervals with similar correlation strengths from 39 GeV Au+Au to 2.76 TeV Pb+Pb (measured by the ALICE experiment). The $v_{2}$-$v_{4}$ correlation seems to be stronger at 39 GeV than at higher collision energies. The initial-stage anti-correlations between second and third order eccentricities are sufficient to describe the measured correlations between $v_{2}$ and $v_{3}$. The best description of $v_{2}$-$v_{4}$ correlations at $\sqrt{s_{NN}}$ = 200 GeV is obtained with inclusion of the system's nonlinear response to initial eccentricities accompanied by the viscous effect with $\eta/s$ $>$ 0.08. Theoretical calculations using different initial conditions, equations of state and viscous coefficients need to be further explored to extract $\eta/s$ of the medium created at RHIC.
Symmetric cumulant SC(2,3) and SC(2,4) as a function of average number of participant nucleons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Symmetric cumulant SC(2,3) as a function of average number of participant nucleons in Au+Au collisions at $\sqrt{s_{NN}}$ = 39 GeV.
Symmetric cumulant SC(2,4) as a function of average number of participant nucleons in Au+Au collisions at $\sqrt{s_{NN}}$ = 39 GeV.
The azimuthal anisotropic flow of identified and unidentified charged particles has been systematically studied in Cu+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV for harmonics $n=$ 1-4 in the pseudorapidity range $|\eta|<1$. The directed flow in Cu+Au collisions is compared with the rapidity-odd and, for the first time, the rapidity-even components of charged particle directed flow in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200~GeV. The slope of the directed flow pseudorapidity dependence in Cu+Au collisions is found to be similar to that in Au+Au collisions, with the intercept shifted toward positive $\eta$ values, i.e., the Cu-going direction. The mean transverse momentum projected onto the spectator plane, $\langle p_x\rangle$, in Cu+Au collision also exhibits approximately linear dependence on $\eta$ with the intercept at about $\eta\approx-0.4$, closer to the rapidity of the Cu+Au system center-of-mass. The observed dependencies find natural explanation in a picture of the directed flow originating partly due the "tilted source" and partly due to the rapidity dependent asymmetry in the initial density distribution. Charge-dependence of the $\langle p_x\rangle$ was also observed in Cu+Au collisions, indicating an effect of the initial electric field created by charge difference of the spectator protons in two colliding nuclei. The rapidity-even component of directed flow in Au+Au collisions is close to that in Pb+Pb collisions at $\sqrt{s_{_{NN}}}$ = 2.76 TeV, indicating a similar magnitude of dipole-like fluctuations in the initial-state density distribution. Higher harmonic flow in Cu+Au collisions exhibits similar trends to those observed in Au+Au and Pb+Pb collisions and is qualitatively reproduced by a viscous hydrodynamic model and a multi-phase transport model. For all harmonics with $n\ge2$ we observe an approximate scaling of $v_n$ with the number of constituent quarks.
Directed flow $v_1(\eta)$ and $<p_x>(\eta)$ of charged particles measured with respect to the target and projectile spectator planes in 10%-40% centrality for Cu+Au collisions.
Directed flow $v_1(\eta)$ and $<p_x>(\eta)$ of charged particles measured with respect to the target and projectile spectator planes in 10%-40% centrality for Au+Au collisions.
Conventional and fluctuation components of directed flow $v_1(\eta)$ and momentum shift $<p_x>/<p_T>(\eta)$ of charged particles in 10%-40% centrality for Cu+Au and Au+Au collisions.
The transversity distribution, which describes transversely polarized quarks in transversely polarized nucleons, is a fundamental component of the spin structure of the nucleon, and is only loosely constrained by global fits to existing semi-inclusive deep inelastic scattering (SIDIS) data. In transversely polarized $p^\uparrow+p$ collisions it can be accessed using transverse polarization dependent fragmentation functions which give rise to azimuthal correlations between the polarization of the struck parton and the final state scalar mesons. This letter reports on spin dependent di-hadron correlations measured by the STAR experiment. The new dataset corresponds to 25 pb$^{-1}$ integrated luminosity of $p^\uparrow+p$ collisions at $\sqrt{s}=500$ GeV, an increase of more than a factor of ten compared to our previous measurement at $\sqrt{s}=200$ GeV. Non-zero asymmetries sensitive to transversity are observed at a $Q^2$ of several hundred GeV and are found to be consistent with the former measurement and a model calculation. %we observe consistent with the former measurement are observed.} We expect that these data will enable an extraction of transversity with comparable precision to current SIDIS datasets but at much higher momentum transfers where subleading effects are suppressed.
Squared 4-momentum transfer $Q^2$ vs x coverage of STAR .
$A_{UT}$ as a function of $\eta$ for $<p_{T}>$ = 13 GeV/c and $<M_{inv}>$ = 1 GeV/($c^2$) (Upper panel of the fig. 3). Kinematic variables $<x>$, $<z>$ as a function of $\eta$ for $<p_{T}>$ = 13 GeV/c and $<M_{inv}>$ = 1 GeV/($c^2$) (Lower panel of the fig. 3). In addition to statistical uncertainties, systematic uncertainties originating from PID and trigger bias systematic uncertainties are also mentioned for $A_{UT}$.
$A_{UT}$ as a function of $<M_{inv}>$ for pT bin $<p_{T}>$ = 4 GeV/c for $\eta > 0$ and $\eta < 0$. In addition to statistical uncertainties, systematic uncertainties originating from PID and trigger bias systematic uncertainties are also mentioned.
Forum