D meson nuclear modification factors in Pb-Pb collisions at {\surd}sNN = 2.76 TeV, measured with the ALICE detector

The ALICE experiment has measured the D meson production in pp and Pb-Pb collisions at the LHC at {\surd}s = 7 and 2.76 TeV and {\surd}sNN = 2.76 TeV respectively, via the exclusive reconstruction of hadronic decay channels. The analyses of the D0{\to}K-pi+ and D+{\to}K-pi+pi+ channels will be described and the preliminary results for the D0 and D+ nuclear modification factor will be presented.Comment: Proceedings of Quark Matter 2011 conference. 4 pages, 4 figures. The slides of the talk can be found at the link: http://indico.cern.ch/materialDisplay.py?contribId=591&sessionId=53&materialId=slides&confId=3024

Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions

Within a multiphase transport (AMPT) model, where the initial conditions are obtained from the recently updated HIJING 2.0 model, the recent anisotropic flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC center of mass energy of 2.76 TeV are explored to constrain the properties of the partonic medium formed. In contrast to RHIC, the measured centrality dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe constraint to the largely uncertain gluon shadowing parameter s_g. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With the parton shadowing so constrained, hadron production and flow over a wide transverse momenta range are investigated in AMPT. The model calculations for the elliptic and triangular flow are found to be in excellent agreement with the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC are given. The magnitude and pattern of suppression of the hadrons in AMPT are found consistent with the measurements at RHIC. However, the suppression is distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of the QCD coupling constant alpha_s by ~30% in the higher temperature plasma formed at LHC reproduces the measured hadron suppression.Comment: Talk given by Subrata Pal at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Transverse momentum distributions and their forward- backward correlations in the percolating colour string approach

The forward-backward correlations in the $p_T$ distributions, which present a clear signature of non-linear effects in particle production, are studied in the model of percolating colour strings. Quantitative predictions are given for these correlations at SPS, RHIC and LHC energies. Interaction of strings also naturally explains the flattening of $p_T$ distributions and increase of $$ with energy and atomic number for nuclear collisionsComment: 6 pages in LaTex, 3 figures in Postscrip

NA49/NA61: results and plans on beam energy and system size scan at the CERN SPS

This paper presents results and plans of the NA49 and NA61/SHINE experiments at the CERN Super Proton Synchrotron concerning the study of relativistic nucleus-nucleus interactions. First, the NA49 evidence for the energy threshold of creating quark-gluon plasma, the onset of deconfinement, in central lead-lead collisions around 30A GeV is reviewed. Then the status of the NA61/SHINE systematic study of properties of the onset of deconfinement is presented. Second, the search for the critical point of strongly interacting matter undertaken by both experiments is discussed. NA49 measured large fluctuations at the top SPS energy, 158A GeV, in collisions of light and medium size nuclei. They seem to indicate that the critical point exists and is located close to baryonic chemical potential of about 250 MeV. The NA61/SHINE beam energy and system size scan started in 2009 will provide evidence for the existence of the critical point or refute the interpretation of the NA49 fluctuation data in terms of the critical point.Comment: 11 pages, invited talk at Quark Matter 201

First Results from Pb+Pb collisions at the LHC

At the end of 2010, the CERN Large Hadron Collider started operation with heavy ion beams, colliding lead nuclei at a centre-of-mass energy of 2.76 TeV/nucleon and opening a new era in ultra-relativistic heavy ion physics at energies exceeding previous accelerators by more than an order of magnitude. This review summarizes the results from the first year of heavy ion physics at LHC obtained by the three experiments participating in the heavy ion program, ALICE, ATLAS, and CMS.Comment: To appear in Annual Review of Nuclear and Particle Scienc

Quenching and Tomography from RHIC to LHC

We compare fully perturbative and fully nonperturbative pictures of high-pT energy loss calculations to the first results from LHC. While over-suppressed compared to published ALICE data, parameter-free pQCD predictions based on the WHDG energy loss model constrained to RHIC data simultaneously describe well the preliminary CMS hadron suppression, ATLAS charged hadron v2, and ALICE D meson suppression; we also provide for future reference WHDG predictions for B meson RAA. However, energy loss calculations based on AdS/CFT also qualitatively describe well the RHIC pion and non-photonic electron suppression and LHC charged hadron suppression. We propose the double ratio of charm to bottom quark RAA will qualitatively distinguish between these two energy loss pictures.Comment: 4 pages, 3 figures. Proceedings for Quark Matter 201

Pre-equilibrium evolution of non-abelian plasma

We study the production and the equilibration of a non-Abelian $q\bar{q}$ plasma in an external chromoelectric field, by solving the Boltzmann equation with the non-Abelian features explicitly incorporated. We consider the gauge group $SU(2)$ and show that the colour degree of freedom has a major and dominant role in the dynamics of the system. It is seen that the assumption of the so called Abelian dominance is not justified. Finally, it is also shown that many of the features of microscopic studies of the system appear naturally in our studies as well.Comment: Latex pages 22, figures can be obtained from authors. Submitted to PR

Azimuthal dependence of pion source radii in Pb+Au collisions at 158 A GeV

We present results of a two-pion correlation analysis performed with the Au+Pb collision data collected by the upgraded CERES experiment in the fall of 2000. The analysis was done in bins of the reaction centrality and the pion azimuthal emission angle with respect to the reaction plane. The pion source, deduced from the data, is slightly elongated in the direction perpendicular to the reaction plane, similarly as was observed at the AGS and at RHIC.Comment: 5 pages, 2 figure

Universal Pion Freeze-out in Heavy-Ion Collisions

Based on an evaluation of data on pion interferometry and on particle yields at mid-rapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda_f reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from AGS to RHIC.Comment: 5 pages, 3 figures, revised version resubmitted to PR