A search is presented for lepton-flavor violating decays of the Higgs boson to $\mu\tau$ and e$\tau$. The data set corresponds to an integrated luminosity of 137 fb$^{-1}$ collected at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. No significant excess has been found, and the results are interpreted in terms of upper limits on lepton-flavor violating branching fractions of the Higgs boson. The observed (expected) upper limits on the branching fractions are, respectively, $\mathcal{B}($H $\to\mu\tau)$$\lt$ 0.15 (0.15)% and $\mathcal{B}($H$\to$e$\tau)$ $\lt$ 0.22 (0.16)% at 95% confidence level.
Observed (expected) 95% CL upper limits on $B(H\to\mu\tau)$ for each individual category and combined
Observed (expected) 95% CL upper limits on $B(H\to e\tau)$ for each individual category and combined
Summary of observed and expected upper limits at 95% CL, best fit branching fractions and corresponding constraints on Yukawa couplings for the $H\to\mu\tau$ and $H\to e\tau$ channels
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}$'
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.'
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.
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.
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 $\alpha_{\Lambda (\bar{\Lambda})} = 0.732$.
According to first-principle lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region μB ≤ T c. In this range the ratio, C6=C2, of net-baryon distributions are predicted to be negative. In this Letter, we report the first measurement of the midrapidity net-proton C6=C2 from 27, 54.4, and 200 GeV Au þ Au collisions at the Relativistic Heavy Ion Collider (RHIC). The dependence on collision centrality and kinematic acceptance in (p T , y) are analyzed. While for 27 and 54.4 GeV collisions the C6=C2 values are close to zero within uncertainties, it is observed that for 200 GeV collisions, the C6=C2 ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict mostly positive values except for the most central collisions within uncertainties. These observations seem to favor a smooth crossover in the high-energy nuclear collisions at top RHIC energy.
Event by event net-proton multiplicity, $\Delta N_{p}$, distributions for Au+Au collisions at √sNN = 27, 54.4, and 200 GeV in 0-10% and 30-40% centralities at midrapidity (|y| < 0.5) for the transverse momentum range of 0.4 < $p_{T}$ (GeV/c) < 2.0. These distributions are normalized by the corresponding numbers of events and are not corrected for detector efficiencies. Statistical uncertainties are shown as vertical lines. The dashed lines show the Skellam distributions for each collision energy and centrality. The bottom panel shows the ratio of the data to the Skellam expectations.
Event by event net-proton multiplicity, $\Delta N_{p}$, distributions for Au+Au collisions at √sNN = 27, 54.4, and 200 GeV in 0-10% and 30-40% centralities at midrapidity (|y| < 0.5) for the transverse momentum range of 0.4 < $p_{T}$ (GeV/c) < 2.0. These distributions are normalized by the corresponding numbers of events and are not corrected for detector efficiencies. Statistical uncertainties are shown as vertical lines. The dashed lines show the Skellam distributions for each collision energy and centrality. The bottom panel shows the ratio of the data to the Skellam expectations.
Event by event net-proton multiplicity, $\Delta N_{p}$, distributions for Au+Au collisions at √sNN = 27, 54.4, and 200 GeV in 0-10% and 30-40% centralities at midrapidity (|y| < 0.5) for the transverse momentum range of 0.4 < $p_{T}$ (GeV/c) < 2.0. These distributions are normalized by the corresponding numbers of events and are not corrected for detector efficiencies. Statistical uncertainties are shown as vertical lines. The dashed lines show the Skellam distributions for each collision energy and centrality. The bottom panel shows the ratio of the data to the Skellam expectations.
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
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
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)
The polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild $p_T$ dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagree with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and $p_T$ dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy.
$sgn(\alpha_H)\langle\cos(\theta_p^{\ast})\rangle$ of $\Lambda$ and $\bar{\Lambda}$ as a function of hyperon azimuthal angle relative to the second-order event plane in isobar collisions at 200 GeV.
$sgn(\alpha_H)\langle\cos(\theta_p^{\ast})\rangle$ of $\Lambda$ and $\bar{\Lambda}$ as a function of hyperon azimuthal angle relative to the third-order event plane in isobar collisions at 200 GeV.
Several models of physics beyond the Standard Model predict the existence of dark photons, light neutral particles decaying into collimated leptons or light hadrons. This paper presents a search for long-lived dark photons produced from the decay of a Higgs boson or a heavy scalar boson and decaying into displaced collimated Standard Model fermions. The search uses data corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected in proton-proton collisions at $\sqrt{s} =$ 13 TeV recorded in 2015-2016 with the ATLAS detector at the Large Hadron Collider. The observed number of events is consistent with the expected background, and limits on the production cross section times branching fraction as a function of the proper decay length of the dark photon are reported. A cross section times branching fraction above 4 pb is excluded for a Higgs boson decaying into two dark photons for dark-photon decay lengths between 1.5 mm and 307 mm.
Upper limits at 95% CL on the cross section times branching fraction for the process $H \to 2\gamma_d + X$ with $m_H$ = 125 GeV in the muon-muon final state.
Upper limits at 95% CL on the cross section times branching fraction for the process $H \to 4\gamma_d + X$ with $m_H$ = 125 GeV in the muon-muon final state.
Upper limits at 95% CL on the cross section times branching fraction for the process $H \to 2\gamma_d + X$ with $m_H$ = 800 GeV in the muon-muon final state.
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$
Two-particle correlation measurements projected onto two-dimensional, transverse rapidity coordinates ($y_{T1},y_{T2}$), allow access to dynamical properties of the QCD medium produced in relativistic heavy-ion collisions that angular correlation measurements are not sensitive to. We report non-identified charged-particle correlations for Au + Au minimum-bias collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV taken by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Correlations are presented as 2D functions of transverse rapidity for like-sign, unlike-sign and all charged-particle pairs, as well as for particle pairs whose relative azimuthal angles lie on the near-side, the away-side, or at all relative azimuth. The correlations are constructed using charged particles with transverse momentum $p_T \geq 0.15$ GeV/$c$, pseudorapidity from $-$1 to 1, and azimuthal angles from $-\pi$ to $\pi$. The significant correlation structures that are observed evolve smoothly with collision centrality. The major correlation features include a saddle shape plus a broad peak with maximum near $y_T \approx 3$, corresponding to $p_T \approx$ 1.5 GeV/$c$. The broad peak is observed in both like- and unlike-sign charge combinations and in near- and away-side relative azimuthal angles. The all-charge, all-azimuth correlation measurements are compared with the theoretical predictions of {\sc hijing} and {\sc epos}. The results indicate that the correlations for peripheral to mid-central collisions can be approximately described as a superposition of nucleon + nucleon collisions with minimal effects from the QCD medium. Strong medium effects are indicated in mid- to most-central collisions.
Two-dimensional correlations of charged-hadrons, all-CI, projected onto (y_t1, y_t2), in centrality bin 84-93%.
Two-dimensional correlations of charged-hadrons, all-CI, projected onto (y_t1, y_t2), in centrality bin 74-84%.
Two-dimensional correlations of charged-hadrons, all-CI, projected onto (y_t1, y_t2), in centrality bin 64-74%.
Mesons comprising a beauty quark and a strange quark can oscillate between particle (B0s) and antiparticle (B0s) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, deltams. Here we present ameasurement of deltams using B0s2DsPi decays produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The oscillation frequency is found to be deltams = 17.7683 +- 0.0051 +- 0.0032 ps-1, where the first uncertainty is statistical and the second systematic. This measurement improves upon the current deltams precision by a factor of two. We combine this result with previous LHCb measurements to determine deltams = 17.7656 +- 0.0057 ps-1, which is the legacy measurement of the original LHCb detector.
Summary of LHCb measurements. Comparison of LHCb $\Delta m_s$ measurements from Refs. [8–11], the result presented in this article and their average. For the average, following systematic uncertainties are assumed to be fully correlated(:) zScale, MomentumScale, VeloAlignment and DecayTimeBias. The measurements are statistically uncorrelated.
The linear and mode-coupled contributions to higher-order anisotropic flow are presented for Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 27, 39, 54.4, and 200 GeV and compared to similar measurements for Pb+Pb collisions at the Large Hadron Collider (LHC). The coefficients and the flow harmonics' correlations, which characterize the linear and mode-coupled response to the lower-order anisotropies, indicate a beam energy dependence consistent with an influence from the specific shear viscosity ($\eta/s$). In contrast, the dimensionless coefficients, mode-coupled response coefficients, and normalized symmetric cumulants are approximately beam-energy independent, consistent with a significant role from initial-state effects. These measurements could provide unique supplemental constraints to (i) distinguish between different initial-state models and (ii) delineate the temperature ($T$) and baryon chemical potential ($\mu_{B}$) dependence of the specific shear viscosity $\frac{\eta}{s} (T, \mu_B)$.
Comparison of the integrated three-particle correlators for Au+Au collisions at 54.4 GeV.
Comparison of the integrated three-particle correlators for Au+Au collisions at 39.0 GeV.
Comparison of the integrated three-particle correlators for Au+Au collisions at 27.0 GeV.
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 triton ($t$) production in mid-rapidity ($|y| <$ 0.5) Au+Au collisions at $\sqrt{s_\mathrm{NN}}$= 7.7--200 GeV measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider (RHIC). The nuclear compound yield ratio ($\mathrm{N}_t \times \mathrm{N}_p/\mathrm{N}_d^2$), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ($dN_{ch}/d\eta$) and follows a scaling behavior. The $dN_{ch}/d\eta$ dependence of the yield ratio is compared to calculations from coalescence and thermal models. Enhancements in the yield ratios relative to the coalescence baseline are observed in the 0%-10% most central collisions at 19.6 and 27 GeV, with a significance of 2.3$\sigma$ and 3.4$\sigma$, respectively, giving a combined significance of 4.1$\sigma$. The enhancements are not observed in peripheral collisions or model calculations without critical fluctuation, and decreases with a smaller $p_{T}$ acceptance. The physics implications of these results on the QCD phase structure and the production mechanism of light nuclei in heavy-ion collisions are discussed.
Invariant yields of tritons at 7.7 GeV, all centralities. The first uncertainty is statistical uncertainty, the second is systematic uncertainty.
Invariant yields of tritons at 11.5 GeV, all centralities. The first uncertainty is statistical uncertainty, the second is systematic uncertainty.
Invariant yields of tritons at 14.5 GeV, all centralities. The first uncertainty is statistical uncertainty, the second is systematic uncertainty.
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.
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.
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 $\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$.
Rapidity-odd directed flow measurements at midrapidity are presented for $\Lambda$, $\bar{\Lambda}$, $K^\pm$, $K^0_s$ and $\phi$ at $\sqrt{s_{NN}} =$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV in Au+Au collisions recorded by the STAR detector at the Relativistic Heavy Ion Collider. These measurements greatly expand the scope of data available to constrain models with differing prescriptions for the equation of state of quantum chromodynamics. Results show good sensitivity for testing a picture where flow is assumed to be imposed before hadron formation and the observed particles are assumed to form via coalescence of constituent quarks. The pattern of departure from a coalescence-inspired sum-rule can be a valuable new tool for probing the collision dynamics.
Directed flow $v_1$ as a function of rapidity $y$ for $p$ in 5%–10% central Au+Au collisions at $\sqrt{s_{NN}} =$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV.
Directed flow $v_1$ as a function of rapidity $y$ for $K^{+}$ in 5%–10% central Au+Au collisions at $\sqrt{s_{NN}} =$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV.
Directed flow $v_1$ as a function of rapidity $y$ for $p$ in 10%–40% central Au+Au collisions at $\sqrt{s_{NN}} =$ 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV.
Additional spin-0 particles appear in many extensions of the standard model. We search for long-lived spin-0 particles $S$ in $B$-meson decays mediated by a $b\to s$ quark transition in $e^+e^-$ collisions at the $\Upsilon(4S)$ resonance at the Belle II experiment. Based on a sample corresponding to an integrated luminosity of $189 \mathrm{\,fb}^{-1}$, we observe no evidence for signal. We set model-independent upper limits on the product of branching fractions $\mathrm{Br}(B^0\to K^*(892)^0(\to K^+\pi^-)S)\times \mathrm{Br}(S\to x^+x^-)$ and $\mathrm{Br}(B^+\to K^+S)\times \mathrm{Br}(S\to x^+x^-)$, where $x^+x^-$ indicates $e^+e^-, \mu^+\mu^-, \pi^+\pi^-$, or $K^+K^-$, as functions of $S$ mass and lifetime at the level of $10^{-7}$.
Expected and observed candidates for $\mathcal{B}($$B^+\to K^+S$$) \times$ $\mathcal{B}($$S\to e^+e^-$) as a function of the reduced mediator candidate mass.
Expected and observed candidates for $\mathcal{B}($$B^+\to K^+S$$) \times$ $\mathcal{B}($$S\to \mu^+\mu^-$) as a function of the reduced mediator candidate mass.
Expected and observed candidates for $\mathcal{B}($$B^+\to K^+S$$) \times$ $\mathcal{B}($$S\to \pi^+\pi^-$) as a function of the reduced mediator candidate mass.
A precise measurement of the hypertriton lifetime is presented. In this letter, the mesonic decay modes $\mathrm{{^3_\Lambda}H \rightarrow ^3He + \pi^-}$ and $\mathrm{{^3_\Lambda}H \rightarrow d + p + \pi^-}$ are used to reconstruct the hypertriton from Au+Au collision data collected by the STAR collaboration at RHIC. A minimum $\chi^2$ estimation is used to determine the lifetime of $\tau = 142^{+24}_{-21}\,{\rm (stat.)} {\pm} 31\,{\rm (syst.)}$ ps. This lifetime is about 50\% shorter than the lifetime $\tau = 263\pm2$ ps of a free $\Lambda$, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R.$_{(^3{\rm He}+\pi^-)}/$(B.R.$_{(^3{\rm He}+\pi^-)}+$B.R.$_{(d+p+\pi^-)})$ = $0.32\rm{\pm}0.05\,{\rm (stat.)}\pm 0.08\,{\rm (syst.)}$. Our ratio result favors the assignment $J(\mathrm{^{3}_{\Lambda}H})$ = $\frac{1}{2}$ over $J(\mathrm{^{3}_{\Lambda}H})$ = $\frac{3}{2}$. These measurements will help to constrain models of hyperon-baryon interactions.
The hypertriton yield as a function of ~l/βγ for each of the two analyzed decay channels. The redpoints are for 2-body decays in four bins of ~l/βγ. The yields indicate the number of $^3_{\Lambda}$H per million events for each channel, and are already divided by the theoretical branching ratio 24.89% for the 2-body channel. The data points are fitted with the usual radioactive decay function. Using a minimum chisquare estimation.
The hypertriton yield as a function of l/βγ for each of the two analyzed decay channels. The bluesquares are for 3-body decays in four bins of l/βγ. The yield of hypertriton per million events in 3-body correct for theoretical branching ratio 40.06% 3-body channel. The data points are fitted with the usual radioactive decay function. Using a minimum chisquare estimation.
A summary of worldwide $^3_{\Lambda}$H lifetime experimental measurements and theoretical calculations. The two star markers are the STAR collaboration’s measurement published in 2010 and the present analysis. This measurement was based on the 3-body decay channel $^3_{\Lambda}$H→p+d+π−in a nuclear emulsion experiment. The shorter lifetime was attributed to the dissociation of the lightly-bound Λ and deuteron when traveling in a dense medium.
A linearly polarized photon can be quantized from the Lorentz-boosted electromagnetic field of a nucleus traveling at ultra-relativistic speed. When two relativistic heavy nuclei pass one another at a distance of a few nuclear radii, the photon from one nucleus may interact through a virtual quark-antiquark pair with gluons from the other nucleus forming a short-lived vector meson (e.g. ${\rho^0}$). In this experiment, the polarization was utilized in diffractive photoproduction to observe a unique spin interference pattern in the angular distribution of ${\rho^0\rightarrow\pi^+\pi^-}$ decays. The observed interference is a result of an overlap of two wave functions at a distance an order of magnitude larger than the ${\rho^0}$ travel distance within its lifetime. The strong-interaction nuclear radii were extracted from these diffractive interactions, and found to be $6.53\pm 0.06$ fm ($^{197} {\rm Au }$) and $7.29\pm 0.08$ fm ($^{238} {\rm U}$), larger than the nuclear charge radii. The observable is demonstrated to be sensitive to the nuclear geometry and quantum interference of non-identical particles.
The $P_T^2 \approx |t|$ distribution of $\rho^0$ collected from Au+Au collisions.
We report the first measurements of transverse single-spin asymmetries for inclusive jet and jet + $\pi^{\pm}$ production at midrapidity from transversely polarized proton-proton collisions at $\sqrt{s} = 500$ GeV. The data were collected in 2011 with the STAR detector sampled from 23 pb$^{-1}$ integrated luminosity with an average beam polarization of 53%. Asymmetries are reported for jets with transverse momenta $6 < p_{T, jet} < 55$ GeV/c and pseudorapidity $|\eta| < 1$. Presented are measurements of the inclusive-jet azimuthal transverse single-spin asymmetry, sensitive to twist-3 initial-state quark-gluon correlators; the Collins asymmetry, sensitive to quark transversity coupled to the polarized Collins fragmentation function; and the first measurement of the "Collins-like" asymmetry, sensitive to linearly polarized gluons. Within the present statistical precision, inclusive-jet and Collins-like asymmetries are small, with the latter allowing the first experimental constraints on gluon linear polarization in a polarized proton. At higher values of jet transverse momenta, we observe the first non-zero Collins asymmetries in polarized-proton collisions, with a statistical significance of greater than $5\sigma$. The results span a range of x similar to results from SIDIS but at much higher $Q^{2}$. The Collins results enable tests of universality and factorization-breaking in the transverse momentum-dependent formulation of perturbative quantum chromodynamics.
Inclusive jet asymmetries $A_{UT}^{\sin(\theta_S)}$ as a function of particle-jet $p_T$.
Inclusive jet asymmetries $A_{UT}^{\sin(\theta_S)}$ as a function of particle-jet $p_T$.
Collins-like asymmetries as a function of particle-jet $p_T$.
The chiral magnetic effect (CME) is predicted to occur as a consequence of a local violation of $\cal P$ and $\cal CP$ symmetries of the strong interaction amidst a strong electro-magnetic field generated in relativistic heavy-ion collisions. Experimental manifestation of the CME involves a separation of positively and negatively charged hadrons along the direction of the magnetic field. Previous measurements of the CME-sensitive charge-separation observables remain inconclusive because of large background contributions. In order to better control the influence of signal and backgrounds, the STAR Collaboration performed a blind analysis of a large data sample of approximately 3.8 billion isobar collisions of $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr at $\sqrt{s_{\rm NN}}=200$ GeV. Prior to the blind analysis, the CME signatures are predefined as a significant excess of the CME-sensitive observables in Ru+Ru collisions over those in Zr+Zr collisions, owing to a larger magnetic field in the former. A precision down to 0.4% is achieved, as anticipated, in the relative magnitudes of the pertinent observables between the two isobar systems. Observed differences in the multiplicity and flow harmonics at the matching centrality indicate that the magnitude of the CME background is different between the two species. No CME signature that satisfies the predefined criteria has been observed in isobar collisions in this blind analysis.
fig2_left_low_isobarpaper_star_blue_case2_zrzr_nonzeros.
fig2_left_low_isobarpaper_star_grey_data_zrzr_nonzeros.
fig2_left_low_isobarpaper_star_red_case3_zrzr_nonzeros.
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.
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 present high-precision measurements of elliptic, triangular, and quadrangular flow $v_{2}$, $v_{3}$, and $v_{4}$, respectively, at midrapidity ($|\eta|<1.0$) for identified hadrons $\pi$, $p$, $K$, $\varphi$, $K_s$, $\Lambda$ as a function of centrality and transverse momentum in Au+Au collisions at the center-of-mass energy $\sqrt{s_{\rm NN}}=$ 200 GeV. We observe similar $v_{n}$ trends between light and strange mesons which indicates that the heavier strange quarks flow as strongly as the lighter up and down quarks. The number-of-constituent-quark scaling for $v_{2}$, $v_{3}$, and $v_{4}$ is found to hold within statistical uncertainty for 0-10$\%$, 10-40$\%$ and 40-80$\%$ collision centrality intervals. The results are compared to several viscous hydrodynamic calculations with varying initial conditions, and could serve as an additional constraint to the development of hydrodynamic models.
The transverse momentum dependence of elliptic, triangular and quadrangular flow of particles, antiparticles and their difference for 0-80 central Au+Au collisions.
The transverse momentum dependence of elliptic, triangular and quadrangular flow of particles, antiparticles and their difference for 0-80 central Au+Au collisions.
The transverse momentum dependence of elliptic, triangular and quadrangular flow of particles, antiparticles and their difference for 0-80 central Au+Au collisions.
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 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.
B B production in π − -uranium interactions has been observed at 320 GeV beam energy looking at events with three muons in the final state. The cross section is found to be σ B B = 4.5±1.4±1.4 nb per nucleon (for a linear A -dependence) or σ B B = 17.6±5.5±5.5 nb per nucleon (assuming A 0.75 dependence). An estimate of x F distribution is given.
BEAUTY INCLUSIVE SPECTRA WAS ASSUMED TO BE E*D(SIG)/D(X)/D(PT**2) = EXP(-0.9*PT**2)*(1-ABS(X))**A. THE BEST FIT FOR A IS A = 2.5.
The influence of collision centrality upon spectra of negative particles produced indC, αC and CC interactions at 4.2 GeV/c per nucleon is studied. The netcharge of secondary particles is used as a measure of collision centrality. Comparison with the nucleon-nucleon collisions and with Dubna intranuclear cascade model is presented. The main features of the momentum, rapidity and angular spectra are compatible with the independent, nucleon-nucleon collision picture. Only in thepT spectra, the observed particle excess, for low and highpT, is inconsistent with this approach. In contrast to the pions, the spectra of protons are more sensitive to the collision centrality.
No description provided.
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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
Elliptic flow measurements from two-, four- and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at $\sqrt{s_{\rm NN}}$= 193 GeV, Cu+Au at $\sqrt{s_{\rm NN}}$= 200 GeV and Au+Au spanning the range $\sqrt{s_{\rm NN}}$= 11.5 - 200 GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and T$\mathrel{\protect\raisebox{-2.1pt}{R}}$ENTo model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.
The Au+Au 200 GeV measurements of the two and four-particle elliptic flow and the elliptic flow fluctuations of the $\pi$ particle.
The Au+Au 200 GeV measurements of the two and four-particle elliptic flow and the elliptic flow fluctuations of the K particle.
The Au+Au 200 GeV measurements of the two and four-particle elliptic flow and the elliptic flow fluctuations of the p particle.
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.
$J/\psi$ 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
Understanding gluon density distributions and how they are modified in nuclei are among the most important goals in nuclear physics. In recent years, diffractive vector meson production measured in ultra-peripheral collisions (UPCs) at heavy-ion colliders has provided a new tool for probing the gluon density. In this Letter, we report the first measurement of $J/\psi$ photoproduction off the deuteron in UPCs at the center-of-mass energy $\sqrt{s_{_{\rm NN}}}=200~\rm GeV$ in d$+$Au collisions. The differential cross section as a function of momentum transfer $-t$ is measured. In addition, data with a neutron tagged in the deuteron-going Zero-Degree Calorimeter is investigated for the first time, which is found to be consistent with the expectation of incoherent diffractive scattering at low momentum transfer. Theoretical predictions based on the Color Glass Condensate saturation model and the gluon shadowing model are compared with the data quantitatively. A better agreement with the saturation model has been observed. With the current measurement, the results are found to be directly sensitive to the gluon density distribution of the deuteron and the deuteron breakup, which provides insights into the nuclear gluonic structure.
Upper - differential cross section as a function of $p^{2}_{T, J/\psi}$ of \jpsi photoproduction in UPCs at $\sqrt{s_{_{\rm NN}}}=200\rm~GeV$. Data for the total diffractive process are shown with solid markers, while data with neutron tagging in the deuteron-going ZDC are shown with open markers. Theoretical predictions based on the saturation model (Color Glass Condensate)[Phys.Rev.C 101 (2020) 1, 015203] and the gluon shadowing model (LTA) [V. Guzey, M. Strikman, E. Kryshen, M. Zhalov] are compared with data, shown as solid lines. Statistical uncertainty is represented by the error bars, and the systematic uncertainty is denoted by the shaded box. For the lower, ratios of total data and models are presented as a function of $-t \approx p^{2}_{T, J/\psi}$. Color bands are statistical uncertainty based on the data only, while systematic uncertainty is indicated by the gray box.
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).
The total cross sections of 18.7 GeV Σ − hyperons on protons and deutrons have been measured to be 34.0 ± 1.1 mb and 61.3 + 1.4 mb, respectively. The derived Σ − -neutron cross section is 30.0 ± 1.2 mb.
CROSS SECTIONS CORRECTED FOR FORWARD COULOMB AND NUCLEAR SCATTERING.
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.
Ratios of the slopes extracted for each system relative to the slope extracted from a fit to the combined data sets
We report on charged hadron production in deuteron-gold reactions at sqrt(s_NN) = 200 GeV. Our measurements in the deuteron-direction cover 1.4 < eta < 2.2, referred to as forward rapidity, and in the gold-direction -2.0 < eta < -1.4, referred to as backward rapidity, and a transverse momentum range p_T = 0.5-4.0 GeV/c. We compare the relative yields for different deuteron-gold collision centrality classes. We observe a suppression relative to binary collision scaling at forward rapidity, sensitive to low momentum fraction (x) partons in the gold nucleus, and an enhancement at backward rapidity, sensitive to high momentum fraction partons in the gold nucleus.
$R_{cp}$ as a function of $p_T$ for Punch-Through Hadrons at forward rapidity and backward rapidity for different centrality classes. Systematic uncertainties which are point-to-point uncorrelated (sys-uncorr) and correlated (sys-corr) are shown.
$R_{cp}$ as a function of $p_T$ for Hadron Decay Muons at forward rapidity and backward rapidity for different centrality classes. Systematic uncertainties which are point-to-point uncorrelated (sys-uncorr) and correlated (sys-corr) are shown.
$R_{cp}$ as a function of $\eta$ for 1.5 < $p_T$ < 4.0 GeV/$c$ for different centrality classes. Systematic uncertainties which are point-to-point uncorrelated (sys-uncorr) and correlated (sys-corr) are shown.
Decays of the 125 GeV Higgs boson into a Z boson and a $\rho^0$(770) or $\phi$(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $\sqrt{s} = $ 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb$^{-1}$. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the $\rho$ and $\phi$ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and $\rho$ or $\phi$ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Z$\rho$ and Z$\phi$ are determined to be 1.04-1.31% and 0.31-0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740-940 and 730-950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels.
Observed and expected 95% CL upper limits on B(H $\rightarrow$ Z$\rho$), for different polarizations.
Observed and expected 95% CL upper limits on B(H $\rightarrow$ Z$\phi$), for different polarizations.
We present the first inclusive measurements of the invariant and SoftDrop jet mass in proton-proton collisions at $\sqrt{s}=200$ GeV at STAR. The measurements are fully corrected for detector effects, and reported differentially in both the jet transverse momentum and jet radius parameter. We compare the measurements to established leading-order Monte Carlo event generators and find that STAR-tuned PYTHIA-6 reproduces the data, while LHC tunes of PYTHIA-8 and HERWIG-7 do not agree with the data, providing further constraints on parameter tuning. Finally, we observe that SoftDrop grooming, for which the contribution of wide-angle non-perturbative radiation is suppressed, shifts the jet mass distributions into closer agreement with the partonic jet mass as determined by both PYTHIA-8 and a next-to-leading-logarithmic accuracy perturbative QCD calculation. These measurements complement recent LHC measurements in a different kinematic region, as well as establish a baseline for future jet mass measurements in heavy-ion collisions at RHIC.
The uncorrected jet mass distribution for $R = 0.4$ anti-$k_{\rm{T}}$ jets with $20 < p_{\rm{T,jet}} < 25$ GeV$/c$. Updated to correct a small bug that had shifted the jet mass to slightly smaller values.
The uncorrected jet mass distribution for $R = 0.4$ anti-$k_{\rm{T}}$ jets with $20 < p_{\rm{T,jet}} < 25$ GeV$/c$.
The uncorrected SoftDrop groomed jet mass distribution for $R = 0.4$ anti-$k_{\rm{T}}$ jets with $20 < p_{\rm{T,jet}} < 25$ GeV$/c$. Updated to correct a small bug that had shifted the jet mass to slightly smaller values.
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 systematic measurements of azimuthal anisotropy for strange and multistrange hadrons ($K^{0}_{s}$, $\Lambda$, $\Xi$, and $\Omega$) and $\phi$ mesons at midrapidity ($|y| <$ 1.0) in collisions of U + U nuclei at $\sqrt{s_{NN}} = 193$ GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. Transverse momentum ($p_{\text{T}}$) dependence of flow coefficients ($v_{2}$, $v_{3}$, and $v_{4}$) is presented for minimum bias collisions and three different centrality intervals. Number of constituent quark scaling of the measured flow coefficients in U + U collisions is discussed. We also present the ratio of $v_{n}$ scaled by the participant eccentricity ($\varepsilon_{n}\left\lbrace 2 \right\rbrace$) to explore system size dependence and collectivity in U + U collisions. The magnitude of $v_{2}/\varepsilon_{2}$ is found to be smaller in U + U collisions than that in central Au + Au collisions contradicting naive eccentricity scaling. Furthermore, the ratios between various flow harmonics ($v_{3}/v_{2}^{3/2}$, $v_{4}/v_{2}^{4/2}$) are studied and compared with hydrodynamic and transport model calculations.
Event plane resolution as a function of centrality for $\psi_{2}$, $\psi_{3}$, and $\psi_{4}$ in U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The statistical uncertainties are smaller than the markers.
The $p_{\text{T}}$ dependence of $v_{n}$ coefficients at mid-rapidity ($|y| <$ 1) in minimum bias U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The error bars represent statistical uncertainties. The bands represent point-by-point systematic uncertainties.
The $p_{\text{T}}$ dependence of $v_{n}$ coefficients at mid-rapidity ($|y| <$ 1) in minimum bias U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The error bars represent statistical uncertainties. The bands represent point-by-point systematic uncertainties.
We present results on Λc+ production in 29-GeV e+e− annihilation. The Λc+ are observed via their semileptonic decays to Λe+X and Λμ+X. With radiative corrections, we find σ(e+e−→Λc+X)〉BΛc+→eΛX)= 1.5±0.6±0.5 pb or 0.0038±0.0015±0.0012 Λc+→Λe+X decay per hadronic event, and σ(e+e−Λc+X)B(Λc+→μΛX)= 1.4±1.4±0.4 pb or 0.0035±0.0035±0.0011 Λc+→Λμ+X decay per hadronic event. These results can be used to place constraints on the predictions of various production models.
Cross sections * branching ratio for LAMBDA/C+ production in LAMBDA E+ decay channel.
Cross sections * branching ratio for LAMBDA/C+ production in LAMBDA MU+ decay channel.
Electroproduction of hadrons is studied in the kinematic region W < 2.8 GeV and 0.3 < Q 2 < 1.4 GeV 2 using the DESY streamer chamber. Prong cross sections, charged-particle multiplicities and inclusive π − distributions are presented. The average charged multiplicity is found to be independent of Q 2 in the Q 2 range studied here; however it is lower than in photoproduction. The fraction of forward π − is found to be significantly less in electroproduction than in photoproduction. The 〈 p ⊥ 2 〉 for inclusive π − is, for all x values, similar to that found in photoproduction.
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