The STAR Time Projection Chamber (TPC) is used to record the collisions at the Relativistic Heavy Ion Collider. The TPC is the central element in a suite of detectors that surrounds the interaction ...vertex. The TPC provides complete coverage around the beam-line, and provides complete tracking for charged particles within ±1.8 units of pseudo-rapidity of the center-of-mass frame. Charged particles with momenta greater than
100
MeV/c
are recorded. Multiplicities in excess of 3000 tracks per event are routinely reconstructed in the software. The TPC measures
4
m
in diameter by
4.2
m
long, making it the largest TPC in the world.
We present the measurement of the transverse single-spin asymmetry of weak boson production in transversely polarized proton-proton collisions at s=500 GeV by the STAR experiment at RHIC. The ...measured observable is sensitive to the Sivers function, one of the transverse-momentum-dependent parton distribution functions, which is predicted to have the opposite sign in proton-proton collisions from that observed in deep inelastic lepton-proton scattering. These data provide the first experimental investigation of the nonuniversality of the Sivers function, fundamental to our understanding of QCD.
We present Lambda Lambda correlation measurements in heavy-ion collisions for Au + Au collisions at root s(NN) = 200 GeV using the STAR experiment at the Relativistic Heavy-Ion Collider. The ...Lednicky-Lyuboshitz analytical model has been used to fit the data to obtain a source size, a scattering length and an effective range. Implications of the measurement of the Lambda Lambda correlation function and interaction parameters for dihyperon searches are discussed.
We present measurements of second-order azimuthal anisotropy (v2) at midrapidity (|y| < 1.0) for light nuclei d,t,3He (for sNN=200, 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV) and antinuclei $ ...\overline{d}\ $; (sNN=200, 62.4, 39, 27, and 19.6 GeV) and 3H$ \overline{e}\ $(sNN=200 GeV) in the STAR (Solenoidal Tracker at RHIC) experiment. The v2 for these light nuclei produced in heavy-ion collisions is compared with those for p and $ \overline{p}\ $. We observe mass ordering in nuclei v2(pT) at low transverse momenta (pT < 2.0 GeV/c). We also find a centrality dependence of v2 for d and $ \overline{d}\ $. The magnitude of v2 for t and 3He agree within statistical errors. Light-nuclei v2 are compared with predictions from a blast-wave model. Atomic mass number (A) scaling of light-nuclei v2(pT) seems to hold for pT/A < 1.5GeV/c. Results on light-nuclei v2 from a transport-plus-coalescence model are consistent with the experimental measurements.
In this paper, we present high precision measurements of elliptic flow near midrapidity (|y|<1.0) for multistrange hadrons and φ meson as a function of centrality and transverse momentum in Au+Au ...collisions at center of mass energy $\sqrt{sNN}$=200 GeV. We observe that the transverse momentum dependence of φ and Ωv2 is similar to that of π and p, respectively, which may indicate that the heavier strange quark flows as strongly as the lighter up and down quarks. This observation constitutes a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. Number of constituent quark scaling is found to hold within statistical uncertainty for both 0%-30% and 30%-80% collision centrality. Finally, there is an indication of the breakdown of previously observed mass ordering between φ and proton v2 at low transverse momentum in the 0%-30% centrality range, possibly indicating late hadronic interactions affecting the proton v2.
We present measurements of Ω and φ production at midrapidity from Au+Au collisions at nucleon-nucleon center-of-mass energies sNN=7.7, 11.5, 19.6, 27, and 39 GeV by the STAR experiment at the BNL ...Relativistic Heavy Ion Collider (RHIC). Motivated by the coalescence formation mechanism for these strange hadrons, we study the ratios of N(Ω-+Ω#x0002B;)/2N(φ). These ratios as a function of transverse momentum pT fall on a consistent trend at high collision energies, but start to show deviations in peripheral collisions at sNN=19.6, 27, and 39 GeV, and in central collisions at 11.5 GeV in the intermediate pT region of 2.4-3.6 GeV/c. We further evaluate empirically the strange quark pT distributions at hadronization by studying the Ω/φ ratios scaled by the number of constituent quarks (NCQ). The NCQ-scaled Ω/φ ratios show a suppression of strange quark production in central collisions at 11.5 GeV compared to sNN≥19.6 GeV. The shapes of the presumably thermal strange quark distributions in 0-60% most central collisions at 7.7 GeV show significant deviations from those in 0-10% most central collisions at higher energies. These features suggest that there is likely a change of the underlying strange quark dynamics in the transition from quark matter to hadronic matter at collision energies below 19.6 GeV.
The second phase of the Beam Energy Scan at RHIC, BES-II, is scheduled for 2019–2020 and will explore with precision measurements the high baryon density region of the QCD phase diagram. The program ...will examine the energy region of interest determined from the results of BES-I. Some of the key measurements anticipated are: the net-protons kurtosis that could pinpoint the position of a critical point, the directed flow that might prove a softening of the EOS, and the chiral restoration in the dilepton channel. The measurements will be possible with the order of magnitude better statistics provided by the electron cooling upgrade of RHIC and with the detector upgrades planned to extend STAR's experimental reach. The upgrades are: the inner TPC sectors (iTPC), the Event Plane Detector (EPD), and the end-cap TOF (eTOF). We present the BES-II program details and the physics opportunities enabled by these upgrades.
We present a measurement of the inclusive production of Υ mesons in U+U collisions at sNN=193 GeV at midrapidity (|y| < 1). Previous studies in central Au+Au collisions at sNN=200 GeV show a ...suppression of Υ(1S+2S+3S) production relative to expectations from the Υ yield in p+p collisions scaled by the number of binary nucleon-nucleon collisions (Ncoll), with an indication that the Υ(1S) state is also suppressed. The present measurement extends the number of participant nucleons in the collision (Npart) by 20% compared to Au+Au collisions, and allows us to study a system with higher energy density. We observe a suppression in both the Υ(1S+2S+3S) and Υ(1S) yields in central U+U data, which consolidates and extends the previously observed suppression trend in Au+Au collisions.
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