In this paper, we present recent STAR J/$psi$ results. J/$psi$ nuclear modification factors ($R_{AA}$) in Au+Au collisions at $sqrt{s_{NN}} =$ 200, 62.4 and 39 GeV and in U+U collisions at $sqrt{s_{NN}} =$ 193 GeV are measured and compared to differe
nt theoretical calculations. We also report J/$psi$ elliptic flow ($v_{2}$) results in Au+Au collisions at $sqrt{s_{NN}} =$ 200 GeV and the first $psi(2S)$ to J/$psi$ ratio measurement in $p+p$ collisions at $sqrt{s} =$ 500 GeV.
RHIC-STAR is a mid-rapidity collider experiment for studying high energy nuclear collisions. The main physics goals of STAR experiment are 1) studying the properties of the strongly coupled Quark Gluon Plasma, 2) explore the QCD phase diagram structu
re. In these proceedings, we will review the recent results of heavy ion physics at STAR.
One of the primary goals of the spin program at the Relativistic Heavy Ion Collider (RHIC) is to determine the polarization of the sea quarks and gluons in the proton. The polarization of the sea quarks is probed through the production of $W^{-(+)}$
bosons via the annihilation of $bar{u}+d,(bar{d}+u)$, at leading order. In this proceedings we report measurements of the single-spin asymmetry, $A_{L}$, for $W$ boson production at $sqrt{s} = 510$ GeV, and the new constraints these results place on the antiquark helicity distributions. Recent results on the longitudinal double-spin asymmetry, $A_{LL}$, for inclusive and di-jet production at $sqrt{s} = 200$ GeV are also presented. The inclusive jet results provide the first experimental indication of non-zero gluon polarization in the $x$ range probed at RHIC.
We report measurements of charmed hadron production from hadronic ($D^{0}rightarrow Kpi$) and semileptonic ($mu$ and $e$) decays in 200 GeV Au+Au collisions at RHIC. Analysis of the spectra indicates that charmed hadrons have a different radial flow
pattern from light or multi-strange hadrons. Charm cross sections at mid-rapidity are extracted by combining the three independent measurements, covering the transverse momentum range that contributes to $sim$90% of the integrated cross section. The cross sections scale with number of binary collisions of the initial nucleons, a signature of charm production exclusively at the initial impact of colliding heavy ions. The implications for charm quark interaction and thermalization in the strongly interacting matter are discussed.
Measurements of three-dimensional correlation functions of like-sign low transverse momentum kaon pairs from Au+Au collisions at top RHIC energy $sqrt s_{NN}$=200 GeV are presented. The extracted kaon source function is narrower than the pion one and
does not have the long tail along the pair transverse momentum direction. This indicates a much smaller role of long-lived resonance decays and/or of the emission duration on kaon emission. Three-dimensional Gaussian shape of the kaon source function can be adequately reproduced by Therminator simulations with resonance contributions taken into account. Comparison to pion data at the same energy reveals that the kaon Gaussian radii in the outward and sideward directions scale with the transverse mass $m_T$. In the longitudinal direction, unlike at lower SPS energies, the Gaussian radii do not seem to follow the exact $m_T$ scaling between kaons and pions.
We present STAR measurements of K^{0}_{S}, phi, Lambda, Xi, and Omega at mid-rapidity from Au+Au collisions at sqrt{s_{NN}} = 7.7, 11.5, 19.6, 27, and 39 GeV from the Beam Energy Scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC). N
uclear modification factors and baryon-to-meson ratios are measured to understand recombination and parton energy loss mechanisms. Implications on partonic versus hadronic dynamics at low beam energies are discussed.
The nuclear modification factors R_{AA} and R_{CP} have been used to measure medium-induced suppression in heavy-ion collisions at sqrt{s_{NN}} = 200GeV which was among the earliest evidence for the existence of a strongly interacting medium called a
quark-gluon plasma (QGP). Nuclear modification factors for asymmetric collisions (R_{dA}) have measured the Cronin Effect, an enhancement of high transverse momentum particle yields in deuteron-gold collisions relative to proton-proton collisions. A similar enhancement is observed in data presented in these proceedings and competes with the quenching caused by partonic energy loss in the QGP. In these proceedings we will present charged-hadron R_{CP} at mid-rapidity for sqrt{s_{NN}} = 7.7 - 62.4GeV as well as identified pi^{+}, K^{+}, and proton R_{CP}. Comparisons to HIJING motivate possible methods for disentangling competing modifications to nuclear transverse momentum spectra.
The production of $W$ bosons in polarized $p+p$ collisions at RHIC provides an excellent tool to probe the protons sea quark distributions. At leading order $W^{-(+)}$ bosons are produced in $bar{u}+d,(bar{d}+u)$ collisions, and parity-violating sing
le-spin asymmetries measured in longitudinally polarized $p+p$ collisions give access to the flavor-separated light quark and antiquark helicity distributions. In this proceedings we report preliminary results for the single-spin asymmetry, $A_L$ from data collected in 2012 by the STAR experiment at RHIC with an integrated luminosity of 72 pb$^{-1}$ at $sqrt{s}=510$ GeV and an average beam polarization of 56%.
We report the energy and centrality dependence of dynamical kurtosis for Au + Au collisions at $sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV at RHIC. The dynamical kurtosis of net-proton is compared to that of total-proton. The results are also compared with AMPT model calculations.
Results from the Beam Energy Scan (BES) program conducted recently by STAR experiment at RHIC are presented. The data from Phase-I of the BES program collected in Au+Au collisions at center-of-mass energies (sqrt{s_{NN}}) of 7.7, 11.5, 19.6, 27, and
39 GeV cover a wide range of baryon chemical potential ?mu_B (100-400 MeV) in the QCD phase diagram. Several STAR results from the BES Phase-I related to turn-off of strongly inter- acting quark-gluon plasma (sQGP) signatures and signals of QCD phase boundary are reported. In addition to this, an outlook is presented for the future BES Phase-II program and a possible fixed target program at STAR.
