The STAR Collaboration reports measurements of the transverse single-spin asymmetries, $A_N$, for inclusive jets and identified `hadrons within jets' production at midrapidity from transversely polarized $pp$ collisions at $\sqrt{s}$ = 200 GeV, based on data recorded in 2012 and 2015. The inclusive jet asymmetry measurements include $A_N$ for inclusive jets and $A_N$ for jets containing a charged pion carrying a momentum fraction $z>0.3$ of the jet momentum. The identified hadron within jet asymmetry measurements include the Collins effect for charged pions, kaons and protons, and the Collins-like effect for charged pions. The measured asymmetries are determined for several distinct kinematic regions, characterized by the jet transverse momentum $p_{T}$ and pseudorapidity $\eta$, as well as the hadron momentum fraction $z$ and momentum transverse to the jet axis $j_{T}$. These results probe higher momentum scales ($Q^{2}$ up to $\sim$ 900 GeV$^{2}$) than current, semi-inclusive deep inelastic scattering measurements, and they provide new constraints on quark transversity in the proton and enable tests of evolution, universality and factorization breaking in the transverse-momentum-dependent formalism.
Distribution of the normalized jet yield as a function of detector jet-$p_{T}$ in 2015 data and simulation. The lower panel shows the ratio between data and simulation.
Comparison of data with simulation for charged hadrons within jets in the 2015 data as a function of the hadron longitudinal momentum fraction, $z$, in two different ranges of jet-$p_{T}$.
Comparison of data with simulation for charged hadrons within jets in the 2015 data as a function of the hadron momentum transverse to the jet axis, $j_{T}$, in two different ranges of jet-$p_{T}$.
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%.
Measurement by the STAR experiment at RHIC of the cold nuclear matter (CNM) effects experienced by inclusive $J/\psi$ at mid-rapidity in 0-100%$p$+Au collisions at $\sqrt{s_{_{\mathrm{NN}}}}$ = 200 GeV is presented. Such effects are quantified utilizing the nuclear modification factor, $R_{p\mathrm{Au}}$, obtained by taking a ratio of $J/\psi$ yield in $p$+Au collisions to that in $p$+$p$ collisions scaled by the number of binary nucleon-nucleon collisions. The differential $J/\psi$ yield in both $p$+$p$ and $p$+Au collisions is measured through the dimuon decay channel, taking advantage of the trigger capability provided by the Muon Telescope Detector in the RHIC 2015 run. Consequently, the $J/\psi$$R_{p\mathrm{Au}}$ is derived within the transverse momentum ($p_{\mathrm{T}}$) range of 0 to 10 GeV/$c$. A suppression of approximately 30% is observed for $p_{\mathrm{T}}<2$ GeV/$c$, while $J/\psi$ $R_{p\mathrm{Au}}$ becomes compatible with unity for $p_{\mathrm{T}}$ greater than 3 GeV/$c$, indicating the $J/\psi$ yield is minimally affected by the CNM effects at high $p_{\mathrm{T}}$. Comparison to a similar measurement from 0-20% central Au+Au collisions reveals that the observed strong $J/\psi$ suppression above 3 Gev/$c$ is mostly due to the hot medium effects, providing strong evidence for the formation of the quark-gluon plasma in these collisions. Several model calculations show qualitative agreement with the measured $J/\psi$ $R_{p\mathrm{Au}}$, while their agreement with the $J/\psi$ yields in $p$+$p$ and $p$+Au collisions is worse.
Inclusive J/psi cross section times branching ratio of the dimuon decay channel in p+p collisions at 200 GeV. Global uncertainty of 12.5% not shown.
Inclusive J/psi cross section times branching ratio of the dimuon decay channel in p+Au collisions at 200 GeV. Global uncertainty of 1.5% not shown.
R_pAu of inclusive J/psi in p+Au collisions at 200 GeV. Global uncertainty of 13.9% not shown.
We report precision measurements of hypernuclei ${}^3_\Lambda \rm{H}$ and ${}^4_\Lambda \rm{H}$ lifetimes obtained from Au+Au collisions at \snn = 3.0 GeV and 7.2 GeV collected by the STAR experiment at RHIC, and the first measurement of ${}^3_\Lambda \rm{H}$ and ${}^4_\Lambda \rm{H}$ mid-rapidity yields in Au+Au collisions at \snn = 3.0 GeV. ${}^3_\Lambda \rm{H}$ and ${}^4_\Lambda \rm{H}$, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be $221\pm15(\rm stat.)\pm19(\rm syst.)$ ps for ${}^3_\Lambda \rm{H}$ and $218\pm6(\rm stat.)\pm13(\rm syst.)$ ps for ${}^4_\Lambda \rm{H}$. The $p_T$-integrated yields of ${}^3_\Lambda \rm{H}$ and ${}^4_\Lambda \rm{H}$ are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of ${}^4_\Lambda \rm{H}$ is different for 0--10% and 10--50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the ${}^3_\Lambda \rm{H}$ yield well, while underestimating the ${}^4_\Lambda \rm{H}$ yield. Transport models, combining baryonic mean-field and coalescence (JAM) or utilizing dynamical cluster formation via baryonic interactions (PHQMD) for light nuclei and hypernuclei production, approximately describe the measured ${}^3_\Lambda \rm{H}$ and ${}^4_\Lambda \rm{H}$ yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.
The measured $^{3}_{\Lambda}$H and $^{4}_{\Lambda}$H lifetimes from STAR (2021)
B.R. times dN/dy of $^{3}_{\Lambda}$H vs y in 3 GeV 0-10% Au+Au collisions
B.R. times dN/dy of $^{4}_{\Lambda}$H vs y in 3 GeV 0-10% Au+Au collisions
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 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 report the measurement of $K^{*0}$ meson at midrapidity ($|y|<$ 1.0) in Au+Au collisions at $\sqrt{s_{\rm NN}}$~=~7.7, 11.5, 14.5, 19.6, 27 and 39 GeV collected by the STAR experiment during the RHIC beam energy scan (BES) program. The transverse momentum spectra, yield, and average transverse momentum of $K^{*0}$ are presented as functions of collision centrality and beam energy. The $K^{*0}/K$ yield ratios are presented for different collision centrality intervals and beam energies. The $K^{*0}/K$ ratio in heavy-ion collisions are observed to be smaller than that in small system collisions (e+e and p+p). The $K^{*0}/K$ ratio follows a similar centrality dependence to that observed in previous RHIC and LHC measurements. The data favor the scenario of the dominance of hadronic re-scattering over regeneration for $K^{*0}$ production in the hadronic phase of the medium.
$p_{\mathrm T}$-differential yield of $\mathrm{K^{*0}} + \bar{\mathrm{K^{*0}}}$ in AuAu collisions at $\sqrt{s_{\mathrm{NN}}}~=~$7.7 GeV (Multiplicity class 0-20%).
$p_{\mathrm T}$-differential yield of $\mathrm{K^{*0}} + \bar{\mathrm{K^{*0}}}$ in AuAu collisions at $\sqrt{s_{\mathrm{NN}}}~=~$7.7 GeV (Multiplicity class 20-40%).
$p_{\mathrm T}$-differential yield of $\mathrm{K^{*0}} + \bar{\mathrm{K^{*0}}}$ in AuAu collisions at $\sqrt{s_{\mathrm{NN}}}~=~$7.7 GeV (Multiplicity class 40-60%).
Measurements of mass and $\Lambda$ binding energy of $\rm ^4_{\Lambda}H$ and $\rm ^4_{\Lambda}He$ in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=3$ GeV are presented, with an aim to address the charge symmetry breaking (CSB) problem in hypernuclei systems with atomic number A = 4. The $\Lambda$ binding energies are measured to be $\rm 2.22\pm0.06(stat.) \pm0.14(syst.)$ MeV and $\rm 2.38\pm0.13(stat.) \pm0.12(syst.)$ MeV for $\rm ^4_{\Lambda}H$ and $\rm ^4_{\Lambda}He$, respectively. The measured $\Lambda$ binding-energy difference is $\rm 0.16\pm0.14(stat.)\pm0.10(syst.)$ MeV for ground states. Combined with the $\gamma$-ray transition energies, the binding-energy difference for excited states is $\rm -0.16\pm0.14(stat.)\pm0.10(syst.)$ MeV, which is negative and comparable to the value of the ground states within uncertainties. These new measurements on the $\Lambda$ binding-energy difference in A = 4 hypernuclei systems are consistent with the theoretical calculations that result in $\rm \Delta B_{\Lambda}^4(1_{exc}^{+})\approx -\Delta B_{\Lambda}^4(0_{g.s.}^{+})<0$ and present a new method for the study of CSB effect using relativistic heavy-ion collisions.
The measurement of $\Lambda$ binding energies of $^4_{\Lambda}H$ and $^4_{\Lambda}He$ in ground and excited states.
The measurement of $\Lambda$ binding energy difference between $^4_{\Lambda}H$ and $^4_{\Lambda}He$ in ground states.
The measurement of $\Lambda$ binding energy difference between $^4_{\Lambda}H$ and $^4_{\Lambda}He$ in excited states.
We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum ($p_{\rm T}$) at mid-rapidity ($|y|<$ 0.7) in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV. The result is presented for 2.5 $<p_{\rm T}<$ 10 GeV/$c$ with an improved precision above 6 GeV/$c$ with respect to the previous measurements, providing more constraints on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.
Signal-to-background ratio as a function of $p_{T}$, where the signals are non-photonic electrons [$N_{\rm INE}\times P_{\rm e} - N_{\rm PHE}/\varepsilon_{PHE}$ in Eq.$1$ shown in paper text] and the backgrounds are photonic electrons [$N_{\rm PHE}/\varepsilon_{PHE}$ in Eq.$1$], in $p$+$p$ collisions at $\sqrt{s}=200$ GeV. The vertical bars represent statistical uncertainties while the boxes represent systematic uncertainties.
Invariant cross sections of the 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) contributions (solid line) in $p$+$p$ collisions at $\sqrt{s}=200$ GeV. The bands represent systematic uncertainties.
(a) The NPE (non-photonic electron) cross section after subtracting the light vector meson contribution at STAR in $p$+$p$ collisions at $\sqrt{s}=200$ GeV from $2012$ (filled circles) along with published STAR data from $2005$ and $2008$ (filled down triangles), published PHENIX data from $2005$ (filled up triangles) and power-law fit (curve). (b) Ratio of data over power-law fit. The vertical bars and the boxes represent statistical and systematic uncertainties, respectively.
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.
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