# Nuclear Theory Seminars at Texas A&M: Spring 2012

Location: Cyclotron Building (434), Seminar Room

Feburary 17, 4:00pm
Nuclear Seminar
Somnath De -VECC-

"
Centrality dependence of jet quenching at RHIC. "

Abstract
We investigate the system size dependence of jet-quenching by analyzing transverse momentum spectra of neutral pions in Au+Au and Cu+Cu collisions at √sNN =200 GeV for different centralities. The partons are assumed to lose energy by radiating gluons as they traverse the plasma and undergo multiple collisions. The energy loss per collision,$\epsilon$, is taken as proportional E (where E is the energy of the parton),proportional to √E, or a constant depending on the formation time of the radiated gluon. NLO pQCD is used to evaluate pion production by modifying the fragmentation function to account for the energy loss. We reproduce the nuclear modification factor RAA by treating $\epsilon$ as the only free parameter, depending on the centrality and the mechanism of energy loss. These values are seen to explain the nuclear modification of prompt photons, caused by the energy lost by final state quarks before they fragment into photons. They also predict the azimuthal asymmetry of transverse momentum distribution for pions within a factor of two and for prompt photons in a rough agreement with experimental data.
Feburary 24, 4:00pm       Nuclear Seminar
Ahmed M. Hamed -Cyclotron-TAMU-

"

Abstract
World-wide efforts over the past half-century have produced a remarkably successful theoretical framework to describe the fundamental matter constituents and their interactions, known as the Standard Model (SM). The SM of particle physics predicts two phase transitions that are relevant for the evolution of the early universe. One is responsible for the spontaneous electroweak symmetry breaking, and the other is related to the spontaneous chiral symmetry breaking and confinement. The relativistic heavy ion collisions provide a unique opportunity to explore the second phase transition, which created 98% of the visible mass of our universe. Energy density and temperature are two basic quantities to describe the medium created in heavy-ion collisions, the Quark Gluon Plasma (QGP). Among many other measurements; the gamma-jet coincidence measurement was suggested to study the medium energy density, and the heavy quarkonia and its excited states were proposed to help place limits on the medium temperature and signify the deconfinment. In this talk, after setting the stage for studying relativistic heavy-ion collisions, I review the present results of direct gamma and heavy quarkonia at STAR experiment, and discuss the relevant questions that we are currently addressing at the Relativistic Heavy Ion Collider (RHIC), as well as the Large Hadron Collider (LHC).

March 02, 4:00pm
Nuclear Seminar
Hanzhong Zhang -Central China Normal University-

"

Abstract
Within a next-to-leading order perturbative QCD parton model, suppression of single hadron spectra and away-side hadron spectra associated with a high p_T photon (or hadron) due to parton energy loss is studied in high-energy heavy-ion collisions. Dihadron spectra are found to be more sensitive to quark gluon plasma than single hadron spectra. For gamma-triggered hadrons, volume emission of gamma-associated parton jets is found to dominate small zt hadrons while surface emission dominates large zt hadrons. Initial fluctuation affects jet energy loss. The reduction or increasing for energy loss is found to be related with a competition between the path-length dependence and the local medium density dependence of jet energy loss.
March 08, 11:00am       Nuclear Seminar
Yuki Asakawa, Osaka University-

"
Higher Order Cumulants in Relativistic Heavy Ion Collisions "

Abstract
Recently fluctuation observebles have been measured at several collision energies at RHIC in search of the QCD critical point. I will first explain the importance of higher cumulants of conserved charges, in particular, of the third cumulants. Then, I will argue that the observed proton number cumulants do not reflect the information at the phase transition, but that the information at the phase transition can be reconstructed with the final state proton and antiproton fluctuations.
March 09, 4:00pm       Nuclear Seminar
Hendrik van Hees,FIAS,Germany

"
Transport simulations for Heavy Quarks in Heavy-Ion Collisions "

Abstract
Heavy charm and bottom quarks are a valuable probe for the properties of the strongly interacting medium, which is created in relativistic heavy-ion collisions. They are created in the initial hard collisions and then interact with the medium consisting of light quarks and gluons (QGP) and later in its evolution a hot and dense hadron gas. In this talk, I'll discuss a model of heavy-quark transport in the QGP, using a Langevin-Fokker-Planck approach for the heavy quarks moving in the "background medium" described by either thermal fireball models or a fully dynamical simulation using a hybrid model with an ideal hydrodynamic simulation for the bulk evolution and Ultrarelativistic Quantum Molecular Dynamics (UrQMD). I'll also discuss conclusions on some physical properties of the strongly interacting medium like a high degree of collectivity in terms of the flow of a (nearly) ideal fluid and possible explanations for this collective behavior from the underlying microscopic dynamics of its constituents.
March 30 4:00pm       Nuclear Seminar
Taesoo Song ,- TAMU-

"
Quarkonia in heavy-ion collisions "

Abstract
TBA.

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