Viscous hydrodynamics description of ϕ\phi meson production in Au+Au and Cu+Cu collisions

In the Israel-Stewart's theory of 2nd order dissipative hydrodynamics, we have simulated $\phi$ production in Au+Au and Cu+Cu collisions at $\sqrt{s}_{NN}$=200 GeV. Evolution of QGP fluid with viscosity over the entropy ratio $\eta/s$=0.25, thermalised at $\tau_i$=0.2 fm, with initial energy density $\epsilon_i$=5.1 $GeV/fm^3$ explains the experimental data on $\phi$ multiplicity, integrated $v_2$, mean $p_T$, $p_T$ spectra and elliptic flow in central and mid-central Au+Au collisions. $\eta/s$=0.25 is also consistent with centrality dependence of $\phi$ $p_T$ spectra in Cu+Cu collisions. The central energy density in Cu+Cu collisions is $\epsilon_i$=3.48 $GeV/fm^3$.Comment: 8 pages, 10 figures. Recent STAR data on $\phi$ production in Au+Au and Cu+Cu are analysed in viscous hydrodynamic

Can J/ψJ/\psi suppression and pTp_T broadening signal the deconfinement transition at RHIC?

We have analyzed the latest NA50 data on $J/\psi$ suppression in Pb+Pb collisions at CERN SPS. It is shown that a QCD based nuclear absorption model, where $J/\psi$'s are absorbed in nuclear medium could explain the latest NA50 data on the centrality dependence of the $J/\psi$ over Drell-Yan ratio. The model also explains the NA50 data on $J/\psi$ over minimum bias ratio and the $p_T$ broadening of $J/\psi$'s. A QGP based threshold model where all the $J/\psi$'s are suppressed above a threshold density, also explains the data sets with smeared threshold density. Even at RHIC energy, centrality dependence of $J/\psi$ suppression or $p_T$ broadening could not distinguish between the two models.Comment: 8 pages, 8 figures. In the revised version, latest NA50 data (2000 run) on the centrality dependence of $J/\psi$ over Drell-Yan ratio are analysed in the QCD based nuclear absorption model and in the QGP based threshold model. In addition NA50 data on the centrality dependence of $J/\psi$ over minimum bias ratio and $p_T$ broadening of $J/\psi$'s are analysed. Prediction for RHIC Au+Au collisions are give

Centrality dependence of high pTp_T suppression in Au+Au collisions suggest quark matter formation

In a pQCD-based model, we have analyzed the STAR data on the high $p_T$ suppression of charged hadrons, in Au+Au collisions at $\sqrt{s}$=200 GeV. In the jet quenching or the energy loss picture, $p_T$ spectra of charged hadrons as well as the $p_T$ dependence of nuclear modification factor, in all the centrality ranges, are well explained, with nearly a constant relative energy loss, $\Delta E/E=0.56\pm 0.03$. Centrality independence of relative energy loss indicate that the matter produced in central and in peripheral collisions are different, otherwise relative energy loss would have shown strong centrality dependence. Qualitatively, centrality independence of relative energy loss can be understood, if in central Au+Au collisions deconfined matter is produced and the matter remain confined in peripheral collisions.Comment: Revised vesrion 5 pages, 3 figures. After careful analysis, I come to conclude that STAR data possibly indicate quark matter formation in central Au+Au collision

Lattice spacing dependence of phase transition temperature in the classical linear sigma model

We have investigated the phase transition properties of classical linear sigma model. The fields were kept in contact with a heat bath for sufficiently long time such that fields are equilibrated at the temperature of the heat bath. It was shown that the sigma model fields undergoes phase transition, but the transition temperature depend crucially on the lattice spacing. In the continuum limit, the transition temperature tends to zero or at least to a very low value.Comment: 3 pages, 1 figur

Modified Knudsen ansatz and elliptic flow in s\sqrt{s}=14 TeV pp collisions

Assuming that hot spots are formed in initial pp collisions, in a modified Knudsen ansatz, which accounts for the entropy generation in viscous fluid evolution, we have given predictions for elliptic flow in $\sqrt{s}$=14 TeV pp collisions. Predicted flow depends on the number of hot spots and hot spot sizes. If two to four hot spots of size $\approx$0.1 fm are formed in initial pp collisions, in events with multiplicity $n_ {mult}\approx$10-15, modified Knudsen ansatz predicted flow is accessible experimentally in 4th order cumulant method.Comment: 4 pages, 4 figure

Effect of charged particle's multiplicity fluctuations on flow harmonics in even-by-event hydrodynamics

In nucleon-nucleon collisions, charged particle's multiplicity fluctuates. We have studied the effect of multiplicity fluctuation on flow harmonics in nucleus-nucleus collision in event-by-event hydrodynamics. Assuming that the charged particle's multiplicity fluctuations are governed by the negative binomial distribution, the Monte-Carlo Glauber model of initial condition is generalised to include the fluctuations. Explicit simulations with the generalised Monte-Carlo Glauber model initial conditions indicate that the multiplicity fluctuations do not have large effect on the flow harmonics.Comment: 8 pages, 8 figures. Final version to be published in Physical Review C. arXiv admin note: text overlap with arXiv:1204.298

Direct photon production and interferometry in sNN\sqrt{s}_{NN}=200 GeV Au+Au and in sNN\sqrt{s}_{NN}=2.76 TeV Pb+Pb collisions

Direct photon production, in $\sqrt{s_{NN}}$=200 GeV Au+Au and in $\sqrt{s_{NN}}$=2.76 TeV Pb+Pb collisions, are studied in a hydrodynamic model. Ideal hydrodynamic model, initialised to reproduce experimentally charged particle spectra in RHIC and LHC energy, also reproduces the PHENIX and ALICE measurements for the direct photon spectra in Au+Au collisions at RHIC and Pb+Pb collisions at LHC. The model however produces less elliptic flow than in experiment. Discrepancy between experiment and hydrodynamic simulation is comparatively less in Pb+Pb collisions at LHC than in Au+Au collisions at RHIC. We also studied direct photon correlation and determined the HBT radii. In 0-10%-50-60% collisions, HBT radii in Au+Au or in Pb+Pb collisions do not show large centrality dependence. Energy dependence of the HBT radii for direct photons is also not large.Comment: Revised, 8 pages, 8 figure

Jet quenching and neutral pion production in Au+Au collisions at RHIC

In the jet quenching model, we have analysed the PHENIX data on nuclear modification factor of $\pi^0$, in Au+Au collisions at $\sqrt{s}$=200 GeV, and extracted the initial gluon density of the medium produced. In jet quenching, partons lose energy in the medium, depending on the medium density as well as on the in-medium path length. Systematic analysis indicate that in most central (0-10% centrality) collisions, medium density is very large $dN_g/dy \sim$ 2150. Medium density decreases exponentially as the collision centrality decreases and in very peripheral (70-92% centrality) collisions, $dN_g/dy \sim$ 3. Initial energy density of the medium also decreases smoothly from $\epsilon_0 \sim$ 20 $GeV/fm^3$ in most central collisions to $\epsilon_0 \sim$ 3 $GeV/fm^3$ in most peripheral collisions. Very large $dN_g/dy$ or $\epsilon_0$ indicate very dense matter formation in central Au+Au collisions.Comment: 11 pages, 7 figure

Heavy flavor production at RHIC and LHC energy

In a leading order pQCD model, we have studied the heavy flavor production in p+p collisions at RHIC and LHC energy. Leading order pQCD models require a K-factor. At RHIC energy, $\sqrt{s}$=200 GeV, we fix K such that the model reproduces the integrated charm yield, $dN^{c\bar{c}}/dy$, estimated by the STAR and the PHENIX collaboration in p+p collisions. The model then explains the STAR data on the transverse momentum distribution of open charm mesons $(D^0)$ and decay electrons in p+p collisions. The p+p predictions, scaled by the number of binary collisions, also explain the electron spectra in STAR p+d collisions and PHENIX Au+Au collisions in different centrality bins. Assuming that at LHC energy K-factor is of the order of unity, we have used the model to predict the transverse momentum distribution of $D$ and $B$ mesons and also of electrons from semileptonic decay of $D\to e$ and $B\to e$, in p+p collisions at LHC energy, $\sqrt{s}$=14 TeV.Comment: 9 pages, 6 figure

Viscous fluid dynamics

We briefly discuss the phenomenological theory of dissipative fluid. We also present some numerical results for hydrodynamic evolution of QGP fluid with dissipation due to shear viscosity only. Its effect on particle production is also studied.Comment: 4 pages, 5 figures. Presented at the International Workshop on Hadron Physics and Property of High Baryon Density Matter, Xi'an, China, 22-25 Nov. 200