Effect of mass asymmetry on the mass dependence of balance energy

We demonstrate the role of the mass asymmetry on the balance energy (Ebal) by studying asymmetric reactions throughout the periodic table and over entire colliding geometry. Our results, which are almost independent of the system size and as well as of the colliding geometries indicate a sizeable effect of the asymmetry of the reaction on the balance energy.Comment: Journal of Physics - Conference Series - Online end of March (2011

Pedestal and Peak Structure in Jet Correlation

We study the characteristics of correlation between particles in jets produced in heavy-ion collisions. In the framework of parton recombination we calculate the $\eta$ and $\phi$ distributions of a pion associated with a trigger particle. The origin of the pedestal in $\Delta\eta$ is related to the longitudinal expansion of the thermal partons that are enhanced by the energy loss of hard partons traversing the bulk medium. The peaks in $\Delta\eta$ and $\Delta\phi$ are related to the same angular spread of the shower partons in a jet cone. No artificial short- or long-range correlations are put in by hand. A large part of the correlation between hadrons in jets is due to the correlation among the shower partons arising from momentum conservation. Recombination between thermal and shower partons dominates the correlation characterisitics in the intermediate $p_T$ region.Comment: 14 pages in LaTex and 2 figures in ep

Angular hadron correlations probing the early medium evolution

Hard processes are a well calibrated probe to study heavy-ion collisions. However, the information to be gained from the nuclear suppression factor R_AA is limited, hene one has to study more differential observables to do medium tomography. The angular correlations of hadrons associated with a hard trigger appear suitable as they show a rich pattern when going from low p_T to high p_T. Of prime interest is the fate of away side partons with an in-medium pathlength O(several fm). At high p_T the correlations become dominated by the punchtrough of the away side parton with subsequent fragmentation. We discuss what information about the medium density can be gained from the data.Comment: Talk given at the 19th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200

Lambda(1520) production in d+Au collisions at RHIC

Recent results of $\Lambda$(1520) resonance production in d+Au collisions at $\sqrt{s_{\rm NN}} =$ 200 GeV are presented and discussed in terms of the evolution and freeze-out conditions of a hot and dense fireball medium. Yields and spectra are compared to results from p+p and Au+Au collisions. The $\Lambda$(1520)/$\Lambda$ ratio in d+Au collisions ratio is consistent with the ratio in p+p collisions. This suggests a short time for elastic interactions between chemical and thermal freeze-out. One can conclude that the interaction volume in d+Au collisions is small.Comment: 4 Pages, 3 figures, conference proceedings Quark Matter 200

K*(892)0 Production in Relativistic Heavy Ion Collisions at sqrt(s_NN) = 130 GeV

Preliminary results on the K*(892)0 -> pi + K production using the mixed-event technique are presented. The measurements are performed at mid-rapidity by the STAR detector in sqrt(s_NN) = 130 GeV Au-Au collisions at RHIC. The K*0 to negative hadron, kaon and phi ratios are obtained and compared to the measurements in e+e-, pp and pbarp at various energies.Comment: 8 pages, 3 figures, proceedings of Strange Quarks in Matter (SQM2001), Frankfurt am Main, Germany, to be published in J. Phys.

Influence of momentum-dependent interactions on balance energy and mass dependence

We aim to study the role of momentum-dependent interactions in transverse flow as well as in its disappearance. For the present study, central collisions involving mass between 24 and 394 are considered. We find that momentum-dependent interactions have different impact in lighter colliding nuclei compared to heavier colliding nuclei. In lighter nuclei, the contribution of mean field towards the flow is smaller compared to heavier nuclei where binary nucleon-nucleon collisions dominate the scene. The inclusion of momentum-dependent interactions also explains the energy of vanishing flow in $^{12}C+^{12}C$ reaction which was not possible with the static equation of state. An excellent agreement of our theoretical attempt is found for balance energy with experimental data throughout the periodic table

Disappearance of Transverse Flow in Central Collisions for Heavier Nuclei

For the first time, mass dependence of balance energy only for heavier systems has been studied. Our results are in excellent agreement with the data which allow us to predict the balance energy of U+U, for the first time, around 37-39 MeV/nucleon. Also our results indicate a hard equation of state along with nucleon-nucleon cross-section around 40 mb.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Particle Ratios, Equilibration, and the QCD Phase Boundary

We discuss the status of thermal model descriptions of particle ratios in central nucleus-nucleus collisions at ultra-relativistic energy. An alternative to the ``Cleymans-Redlich'' interpretation of the freeze-out trajectory is given in terms of the total baryon density. Emphasis is placed on the relation between the chemical equilibration parameters and the QCD phase boundary. Furthermore, we trace the essential difference between thermal model analyses of data from collisions between elementary particles and from heavy ion collisions as due to a transition from local strangeness conservation to percolation of strangeness over large volumes, as occurs naturally in a deconfined medium. We also discuss predictions of the thermal model for composite particle production.Comment: Contribution to SQM2001 Conference, submitted to J. Phys.

Does HBT Measure the Freeze-out Source Distribution?

It is generally assumed that as a result of multiple scattering, the source distribution measured in HBT interferometry corresponds to a chaotic source at freeze-out. This assumption is subject to question as effects of multiple scattering in HBT measurements must be investigated within a quantum-mechanical framework. Applying the Glauber multiple scattering theory at high energies and the optical model at lower energies, we find that multiple scattering leads to an effective HBT density distribution that depends on the initial chaotic source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004, Oakland, California, USA, to be published in the Proceeding

Evidence for chemical equilibration at RHIC

This contribution focuses on the results of statistical model calculations at RHIC energies, including recently available experimental data. Previous calculations of particle yield ratios showed good agreement with measurements at SPS and lower energies, suggesting that the composite system possesses a high degree of chemical equilibrium at freeze-out. The effect of feeddown contamination on the model parameters is discussed, and the sensitivity of individual ratios to the model parameters ($T$, $\mu_B$) is illustrated.Comment: Talk presented at Strange Quarks in Matter 2001, Frankfurt, September 24-29, 2001. Proceedings to be published by J. Phys. G. 8 pages with 4 figure