Characteristics of Parton Energy Loss Studied with High-p_T Particle Spectra from PHENIX

In the first three years of the physics program at the Relativistic Heavy Ion Collider (RHIC) a picture was established in which the suppression of hadrons at high transverse momenta (p_T) in central Au+Au collisions is explained by energy loss of quark and gluon jets in a medium of high color-charge density. Measurements of single particle spectra for a smaller nucleus (Cu), for different center-of-mass energies and with higher statistics were performed in the subsequent years and are used to test predictions and assumptions of jet quenching models in more detail. The measurements presented here are consistent with a parton energy loss scenario so that these models can be used to relate the observed suppression to properties of the created medium.Comment: To appear in the proceedings of 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 04-10 Feb 200

In-medium hadronization in the deconfined matter at RHIC and LHC

We study the mechanism and probability of in-medium hadronization in the deconfined medium produced in heavy-ion collisions at RHIC and LHC. We show the likelihood of color-neutral objects to be formed inside the partonic fireball and the probability of these states to escape the medium with reduced interaction strength and energy loss. We will suggest specific measurements that are sensitive to the early degrees of freedom and show predictions for these measurements at RHIC and the LHCComment: 8 pages, 6 figures, submitted to PL

Highlights from PHENIX - II

This contribution highlights recent results from the PHENIX Collaboration at RHIC with emphasis on those obtained through lepton and photon measurements in PHENIX.Comment: 9 pages, 13 figures, presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions - "Quark Matter 2008", Jaipur, India, February 4-10, 200

Jet quenching and direct photon production

Jet quenching effect has been investigated in the direct photon production, based on a realistic data-constrained (3+1) dimensional hydrodynamic description of the expanding hot and dense matter, a reasonable treatment of the propagation of partons and their energy loss in the fluid, and a systematic study of the main sources of direct photons. Our resultant \pt spectra agree with recent PHENIX data in a broad \pt range. Parton energy loss in the plasma eventually effect significantly direct photon production from fragmentation and jet photon conversion, similar to hadron suppression in central heavy ion collisions. But this only causes about 40% decrease in the total production of direct photons, due to the mixture with other direct photon sources.Comment: 6 pages and 3 figures, To appear in the proceedings of the International Conference on Strangeness in Quark matter (SQM2008), Beijing, China, Oct 6-10, 200

Quarkonia Measurements with STAR

We report results on quarkonium production from the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). J/psi spectra in p+p and Cu+Cu collisions at sqrt(s) = 200 GeV with transverse momenta in the range of 0.5-14 GeV/c and 5-8 GeV/c, respectively, are presented. We find that for p_T > 5 GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu collisions scaled with the respective number of binary nucleon-nucleon collisions. In this range the nuclear modification factor, R_AA, is measured to be 0.9+-0.2(stat). For the first time at RHIC, high-p_T J/psi-hadron correlations were studied in p+p collisions. Implications from our measurements on J/psi production mechanisms, constraints on open bottom yields, and J/psi dissociation mechanisms at high-p_T are discussed. In addition, we give a brief status of measurements of Upsilon production in p+p and Au+Au collisions and present projections of future quarkonia measurements based on an upgrades to the STAR detector and increased luminosity achieved through stochastic cooling of RHIC.Comment: 5 pages, 5 figures. Prepared for 3rd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2008), A Toxa, Spain, June 8-14, 200

Global Analysis of Fragmentation Functions for Eta Mesons

Fragmentation functions for eta mesons are extracted at next-to-leading order accuracy of QCD in a global analysis of data taken in electron-positron annihilation and proton-proton scattering experiments. The obtained parametrization is in good agreement with all data sets analyzed and can be utilized, for instance, in future studies of double-spin asymmetries for single-inclusive eta production. The Lagrange multiplier technique is used to estimate the uncertainties of the fragmentation functions and to assess the role of the different data sets in constraining them.Comment: 11 pages, 8 figures, updated reference

Multi-strange baryon elliptic flow in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV measured with the ALICE detector

We present the results on elliptic flow with multi-strange baryons produced in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV. The analysis is performed with the ALICE detector at LHC. Multi-strange baryons are reconstructed via their decay topologies and the v_2 values are analyzed with the two-particle scalar product method. The p_T differential v_2 values are compared to the VISH2+1 model calculation and to the STAR measurements at 200 GeV in Au+Au collisions. We found that the model describes \Xi and \Omega v_2 measurements within experimental uncertainties. The differential flow of \Xi and \Omega is similar to the STAR measurements at 200 GeV in Au+Au collisions.Comment: Prepared for the Proceedings of the International Conference on "Critical Point and Onset of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201

J/psi production at RHIC-PHENIX

The J/psi is considered to be among the most important probes for the deconfined quark gluon plasma (QGP) created by relativistic heavy ion collisions. While the J/psi is thought to dissociate in the QGP by Debye color screening, there are competing effects from cold nuclear matter (CNM), feed-downs from excited charmonia (chi_c and psi') and bottom quarks, and regeneration from uncorrelated charm quarks. Measurements that can provide information to disentangle these effects are presented in this paper.Comment: 4 pages, 3 figures, conference proceedings: the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2008, Jaipur (India), 4-10 February 2008, submitted to J. Phys. G: Nuclear and Particle Physic

Development of relativistic shock waves in viscous gluon matter

To investigate the formation and the propagation of relativistic shock waves in viscous gluon matter we solve the relativistic Riemann problem using a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio $\eta/s$. We show that an $\eta/s$ ratio larger than 0.2 prevents the development of well-defined shock waves on time scales typical for ultrarelativistic heavy-ion collisions. These findings are confirmed by viscous hydrodynamic calculations.Comment: 4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

Centrality dependence of v2 in Au + Au at sqrt{s_NN} = 200 GeV

One of the most striking results is the large elliptic flow ($v_2$) at RHIC. Detailed mass and transverse momentum dependence of elliptic flow are well described by ideal hydrodynamic calculations for $p_{\mathrm{T}} <$ 1 GeV/c, and by parton coalescence/recombination picture for $p_{\mathrm{T}} = 2 - 6$ GeV/c. The systematic error on $v_2$ is dominated by so-called "non-flow effects", which is the correlation not originated from reaction plane. It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision dynamics. In this paper, we present the centrality dependence of $v_2$ with respect to the first harmonic event plane at ZDC-SMD ($v_2$\{ZDC-SMD\}) in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Large rapidity gap ($|\Delta\eta| > 6$) between midrapidity and the ZDC could enable us to minimize possible non-flow contributions. We compare the results of $v_2$\{ZDC-SMD\} with $v_2$\{BBC\}, which is measured by event plane determined at $|\eta| = 3.1 - 3.9$. Possible non-flow contributions in those results will be discussed.Comment: 4 pages, 5 figures, conference proceedings for Hot Quarks 200