Measurement of heavy-flavor production in Pb-Pb collisions at the LHC with ALICE

A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC) has been built in order to study the Quark-Gluon Plasma (QGP) created in high-energy nuclear collisions. As heavy-flavor quarks are produced at the early stage of the collision, they serve as sensitive probes for the QGP. The ALICE detector with its capabilities such as particle identification, secondary vertexing and tracking in a high multiplicity environment can address, among other measurements, the heavy-flavor sector in heavy-ion collisions. We present latest results on the measurement of the nuclear modification factor of open heavy-flavors as well as on the measurement of open heavy-flavor azimuthal anisotropy v2 in Pb-Pb collisions at sqrt(s) = 2.76 TeV. Open charmed hadrons are reconstructed in the hadronic decay channels D0->Kpi, D+->Kpipi, and D*+->D0pi applying a secondary decay-vertex topology. Complementary measurements are performed by detecting electrons (muons) from semi-leptonic decays of open heavy-flavor hadrons in the central (forward) rapidity region.Comment: 10 pages, 6 figures. Talk given by Robert Grajcarek 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

First Result of Net-Charge Jet-Correlations from STAR

We presented results on azimuthal correlation of net-charge with high $p_T$ trigger particles. It is found that the net-charge correlation shape is similar to that of total-charge. On the near-side, the net-charge and total-charge $p_T$ spectra have similar shape and both are harder than the inclusives. On the away-side, the correlated spectra are not much harder than the inclusives, and the net-charge/total-charge ratio increases with $p_T$ and is similar to the inclusive ratio

Systematic study of the jet fragmentation function for inclusive jet-production in p+p collisions at sqrt{s}=200 GeV in STAR

Jet fragmentation functions measured in e^+e^- and p+\bar{p} experiments are well-described on an inclusive hadron level by QCD-based calculations. Fragmentation is expected to be modified by the presence of a strongly interacting medium, but full theoretical description of this modification must still be developed. It has recently been suggested that particle-identified fragmentation functions may provide additional insight into the processes underlying jet quenching. To assess the applicability of QCD-based fragmentation calculations to RHIC data, and to provide a baseline with which to compare fragmentation function measurements in heavy ion collisions, we present the first measurements of charged hadron and particle-identified fragmentation functions of jets reconstructed via a midpoint-cone algorithm from p+p collisions at 200 GeV in STAR. We study the dependence on jet cone-size and jet-energy, and compare the results to PYTHIA simulations based on the Modified Leading Log Approximation (MLLA).Comment: 6 pages, 5 figures, proceedings of Hard Probes 2008 conferenc

Jet Correlations with Identified Particles from PHENIX: Methods and Results

Azimuthal angle two particle correlations have been shown to be a powerful probe for extracting novel features of the interaction between hard scattered partons and the medium produced in Au+Au collisions at RHIC. At intermediate $p_T$, 2-5GeV/c, the jets have been shown to be significantly modified in both their particle composition and their angular distribution compared to p+p collisions. Additionally, angular two particle correlations with identified hadrons provide information on the possible role of modified hadronization scenarios such as partonic recombination, which might allow medium modified jet fragmentation by connecting hard scattered partons to low $p_T$ thermal partons. PHENIX has excellent particle identification capabilities and has developed robust techniques for extracting jet correlations from the large underlying event. We present recent PHENIX results from Au+Au collisions for a variety of $p_T$ and particle type combinations. We also present p+p measurements as a baseline. We show evidence that protons and anti-protons in the $p_T$ region of enhanced baryon and anti-baryon single particle production are produced in close angle pairs of opposite charge and that the strong modifications to the away side shape observed for charged hadron correlations are also present when baryons are correlated.Comment: talk given at XIth International Workshop on Correlations and Fluctuations in Multiparticle Production, Hangzhou China November 21-24 200

Test of Chemical freeze-out at RHIC

We present the results of a systematic test applying statistical thermal model fits in a consistent way for different particle ratios, and different system sizes using the various particle yields measured in the STAR experiment. Comparison between central and peripheral Au+Au and Cu+Cu collisions with data from p+p collisions provides an interesting tool to verify the dependence with the system size. We also present a study of the rapidity dependence of the thermal fit parameters using available data from RHIC in the forward rapidity regions and also using different parameterization for the rapidity distribution of different particles.Comment: SQM2008 conference proceeding

Constraining the initial temperature and shear viscosity in a hybrid hydrodynamic model of sNN\sqrt{s_{NN}}=200 GeV Au+Au collisions using pion spectra, elliptic flow, and femtoscopic radii

A new framework for evaluating hydrodynamic models of relativistic heavy ion collisions has been developed. This framework, a Comprehesive Heavy Ion Model Evaluation and Reporting Algorithm (CHIMERA) has been implemented by augmenting UVH 2+1D viscous hydrodynamic model with eccentricity fluctuations, pre-equilibrium flow, and the Ultra-relativistic Quantum Molecular Dynamic (UrQMD) hadronic cascade. A range of initial temperatures and shear viscosity to entropy ratios were evaluated for four initial profiles, $N_{part}$ and $N_{coll}$ scaling with and without pre-equilibrium flow. The model results were compared to pion spectra, elliptic flow, and femtoscopic radii from 200 GeV Au+Au collisions for the 0--20% centrality range.Two sets of initial density profiles, $N_{part}$ scaling with pre-equilibrium flow and $N_{coll}$ scaling without were shown to provide a consistent description of all three measurements.Comment: 21 pages, 32 figures, version 3 includes additional text for clarification, division of figures into more manageable units, and placement of chi-squared values in tables for ease of viewin

Energy Dependence of High Moments for Net-proton Distributions

High moments of multiplicity distributions of conserved quantities are predicted to be sensitive to critical fluctuations. To understand the effect of the complicated non-critical physics backgrounds on the proposed observable, we have studied various moments of net-proton distributions with AMPT, Hijing, Therminator and UrQMD models, in which no QCD critical point physics is implemented. It is found that the centrality evolution of various moments of net-proton distributions can be uniformly described by a superposition of emission sources. In addition, in the absence of critical phenomena, some moment products of net-proton distribution, related to the baryon number susceptibilities ratio in Lattice QCD calculation, are predicted to be constant as a function of the collision centrality. We argue that a non-monotonic dependence of the moment products as a function collision centrality and the beam energy may be used to locate the QCD critical point.Comment: SQM2009 Proceeding, 6 pages, 5 figure