Centrality and Transverse Momentum Dependence of Elliptic Flow of Multistrange Hadrons and \u3cem\u3eϕ\u3c/em\u3e Meson in Au + Au Collisions at √\u3cem\u3e\u3csup\u3es\u3c/sup\u3e\u3csub\u3eNN\u3c/sub\u3e\u3c/em\u3e = 200 GeV

We present high precision measurements of elliptic flow near midrapidity (|y| \u3c 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 √sNN = 200  GeV. We observe that the transverse momentum dependence of ϕ and Ω υ2 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. There is an indication of the breakdown of previously observed mass ordering between ϕ and proton υ2 at low transverse momentum in the 0%–30% centrality range, possibly indicating late hadronic interactions affecting the proton υ2

Energy Dependence of Moments of Net-Proton Multiplicity Distributions at RHIC

We report the beam energy(√8NN = 7.7-200 GeV) and collision centrality dependence of the mean (M), standard deviation (σ), skewness (S), and kurtosis (κ) of the net-proton multiplicity distributions in Au+Au collisions. The measurements are carried out by the STAR experiment at midrapidity (|y|\u3c0.5) and within the transverse momentum range 0.4\u3cρτ\u3c0.8  GeV/c in the first phase of the Beam Energy Scan program at the Relativistic Heavy Ion Collider. These measurements are important for understanding the quantum chromodynamic phase diagram. The products of the moments, Sσ and κσ2, are sensitive to the correlation length of the hot and dense medium created in the collisions and are related to the ratios of baryon number susceptibilities of corresponding orders. The products of moments are found to have values significantly below the Skellam expectation and close to expectations based on independent proton and antiproton production. The measurements are compared to a transport model calculation to understand the effect of acceptance and baryon number conservation and also to a hadron resonance gas model

Centrality Dependence of Identified Particle Elliptic Flow in Relativistic Heavy Ion Collisions at √\u3cem\u3e\u3csup\u3es\u3c/sup\u3e\u3csub\u3eNN\u3c/sub\u3e\u3c/em\u3e = 7.7–62.4 GeV

Elliptic flow (υ2) values for identified particles at midrapidity in Au + Au collisions measured by the STAR experiment in the Beam Energy Scan at the Relativistic Heavy Ion Collider at √sNN = 7.7– 62.4 GeV are presented for three centrality classes. The centrality dependence and the data at √sNN = 14.5 GeV are new. Except at the lowest beam energies, we observe a similar relative υ2 baryon-meson splitting for all centrality classes which is in agreement within 15% with the number-of-constituent quark scaling. The larger υ2 for most particles relative to antiparticles, already observed for minimum bias collisions, shows a clear centrality dependence, with the largest difference for the most central collisions. Also, the results are compared with a multiphase transport (AMPT) model and fit with a blast wave model

Measurement of the Transverse Single-Spin Asymmetry in \u3cem\u3ep\u3c/em\u3e\u3csup\u3e↑\u3c/sup\u3e+\u3cem\u3ep\u3c/em\u3e→\u3cem\u3eW\u3c/em\u3e\u3csup\u3e±\u3c/sup\u3e/\u3cem\u3eZ\u3c/em\u3e\u3csup\u3e0\u3c/sup\u3e at RHIC

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

\u3cem\u3eJ/ψ\u3c/em\u3e Production at Low Transverse Momentum in \u3cem\u3ep\u3c/em\u3e + \u3cem\u3ep\u3c/em\u3e and \u3cem\u3ed\u3c/em\u3e + Au Collisions at √\u3cem\u3e\u3csup\u3es\u3c/sup\u3e\u3csub\u3eNN\u3c/sub\u3e\u3c/em\u3e = 200 GeV

We report on the measurement of J/ψ production in the dielectron channel at midrapidity (|y| \u3c 1) in p + p and d + Au collisions at √sNN = 200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider. The transverse momentum pTspectra in p + p for pT \u3c 4 GeV/c and d + Au collisions for pT \u3c 3 GeV/c are presented. These measurements extend the STAR coverage for J/ψ production in p + p collisions to low pT. The ⟨p2T⟩ from the measured J/ψ invariant cross section in p + p and d + Au collisions are evaluated and compared to similar measurements at other collision energies. The nuclear modification factor for J/ψ is extracted as a function of pT and collision centrality in d + Au and compared to model calculations using the modified nuclear parton distribution function and a final-state J/ψ nuclear absorption cross section