Identified particle transverse momentum spectra in p+p and d+Au collisions at sqrt{s_NN} = 200 GeV

The transverse momentum ($p_{\mathrm T}$) spectra for identified charged pions, protons and anti-protons from $p$+$p$ and $d$+Au collisions are measured around midrapidity ($\mid$y$\mid$ $<$ 0.5) over the range of 0.3 $<$ $p_{\mathrm T}$ $<$ 10 GeV/$c$ at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The charged pion and proton+anti-proton spectra at high p_{T} in p+p collisions have been compared with the next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations with a specific fragmentation scheme. The p/pi^{+} and pbar/pi^{-}has been studied at high p_{T}. The nuclear modification factor (R_{dAu}) shows that the identified particle Cronin effects around midrapidity are significantly non-zero for charged pions and to be even larger for protons at intermediate p_{T} (2 < p_{T} < 5 GeV/c).Comment: Talk given at Particles and Nuclei International Conference, Santa Fe,NM-October 24-28,200

The width of the rapidity distribution in heavy ion collisions

We have studied the widths of the rapidity distributions of particles produced in nucleus-nucleus collisions at various center of mass energies and as a function of centrality at SPS energies. We show that the width of the rapidity distribution is sensitive to longitudinal flow, velocity of sound in the medium, and rescattering of particles. We explore the possibility of distinguishing the initial hard scattering regime from final state effects by studying the variation in the width of the rapidity distribution of the particles with centrality for various pT values.Comment: 4 pages, 6 figures, to appear in Physical Review

Addressing the physics of the ridge by 2- and 3-particle correlations at STAR

We present new results on 2-particle azimuthal ($\Delta\phi$) correlation relative to event plane and 3-particle pseudorapidity ($\Delta\eta$) correlation at mid-rapidity in Au+Au collisions at $\sqrt{{\it s}_{NN}}$ = 200 GeV, measured by the STAR experiment. While jet-like correlation is symmetric, ridge is found to be asymmetric when trigger particle azimuth is between in- and out-of-plane. The charge ordering properties between associated and trigger particles are exploited to separate jet-like and ridge contributions in 3-particle $\Delta\eta$-$\Delta\eta$ correlations. We found that like-sign triplets are dominated by ridge. The separated ridge, while narrow in $\Delta\phi$, is extremely broad in $\Delta\eta$. The ridge particles are not only uncorrelated to the trigger particle in $\Delta\eta$, but also uncorrelated between themselves.Comment: 4 pages, 4 Figures, Quark Matter 200

Selected Experimental Results from Heavy Ion Collisions at LHC

We review a subset of experimental results from the heavy-ion collisions at the Large Hadron Collider (LHC) facility at CERN. Excellent consistency is observed across all the experiments at the LHC (at center of mass energy of 2.76 TeV) for the measurements such as charged particle multiplicity density, azimuthal anisotropy coefficients and nuclear modification factor of charged hadrons. Comparison to similar measurements from the Relativistic Heavy Ion Collider (RHIC) at lower energy (center of mass energy of 200 GeV) suggests that system formed at LHC has a higher energy density, larger system size, and lives for a longer time. These measurements are compared to model calculations to obtain physical insights on the properties of matter created at the RHIC and LHC.Comment: 19 pages and 26 figures. Accepted for publication in the special issue of Advances in High Energy Physics dedicated to Physics of Quark Gluon Plasma: An Update and Status Repor

Energy dependence of elliptic flow from heavy-ion collision models

We have compared the experimental data on charged particle elliptic flow parameter (v2) in Au+Au collisions at midrapidity for \surd sNN = 9.2, 19.6, 62.4 and 200 GeV with results from various models in heavy-ion collisions like UrQMD, AMPT, and HIJING. We observe that the average from the transport model UrQMD agrees well with the measurements at \surd sNN = 9.2 GeV but increasingly falls short of the experimental values as the beam energy increases. The difference in being of the order of 60% at \surd sNN = 200 GeV. The results from HIJING is consistent with zero, while those from AMPT with default settings, a model based on HIJING with additional initial and final state rescattering effects included, gives a value of about 4% for all the beam energies studied. This is in contrast to increase in with beam energy for the experimental data. A different version of the AMPT model, which includes partonic effects and quark coalescence as a mechanism of hadronization, gives higher values of among the models studied and is in agreement with the measured values at \surd sNN = 200 GeV. These studies show that the experimental has substantial contribution from partonic interactions at \surd sNN = 200 GeV whose magnitude reduces with decrease in beam energy. We also compare the available data on the transverse momentum and pseudorapidity dependence of v2 to those from the above models.Comment: 5 pages, 6 figures, accepted in Physical Review

Multiplicity fluctuations in heavy-ion collisions using canonical and grand-canonical ensemble

We report the higher order cumulants and their ratios for baryon, charge and strangeness multiplicity in canonical and grand-canonical ensembles in ideal thermal model including all the resonances. When the number of conserved quanta is small, an explicit treatment of these conserved charges is required, which leads to a canonical description of the system and the fluctuations are significantly different from the grand canonical ensemble. Cumulant ratios of total charge and net-charge multiplicity as a function of collision energies are also compared in grand canonical ensemble.Comment: 7 pages, 5 Figs, Published versio