7 research outputs found
Exploring the QCD landscape with high-energy nuclear collisions
Quantum chromodynamics (QCD) phase diagram is usually plotted as temperature
(T) versus the chemical potential associated with the conserved baryon number
(\mu_{B}). Two fundamental properties of QCD, related to confinement and chiral
symmetry, allows for two corresponding phase transitions when T and \mu_{B} are
varied. Theoretically the phase diagram is explored through non-perturbative
QCD calculations on lattice. The energy scale for the phase diagram
(\Lambda_{QCD} ~ 200 MeV) is such that it can be explored experimentally by
colliding nuclei at varying beam energies in the laboratory. In this paper we
review some aspects of the QCD phase structure as explored through the
experimental studies using high energy nuclear collisions. Specifically, we
discuss three observations related to the formation of a strongly coupled
plasma of quarks and gluons in the collisions, experimental search for the QCD
critical point on the phase diagram and freeze-out properties of the hadronic
phase.Comment: Submitted to the New Journal of Physics focus issue "Strongly
Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD Plasmas
A study on the anomaly of over ratios in collisions with jet quenching
The ratios of at large transverse momentum in central
collisions at RHIC are studied in the framework of jet quenching based on a
next-to-leading order pQCD parton model. It is shown that theoretical
calculations with a gluon energy loss larger than the quark energy loss will
naturally lead to a smaller ratios at large transverse momentum in
collisions than those in collisions at the same energy. Scenarios
with equal energy losses for gluons and quarks and a strong jet conversion are
both explored and it is demonstrated in both scenarios ratios at high
in central collisions are enhanced and the calculated ratios of
protons over pions approach to the experimental measurements. However, in the latter scenario is found to fit data better than that in the
former scenario.Comment: 20 pages, 13 figures; revised version; accepted for publication in
Journal of Physics
Extrapolation of Multiplicity distribution in p+p(\bar(p)) collisions to LHC energies
The multiplicity (N_ch) and pseudorapidity distribution (dN_ch/d\eta) of
primary charged particles in p+p collisions at Large Hadron Collider (LHC)
energies of \sqrt(s) = 10 and 14 TeV are obtained from extrapolation of
existing measurements at lower \sqrt(s). These distributions are then compared
to calculations from PYTHIA and PHOJET models. The existing \sqrt(s)
measurements are unable to distinguish between a logarithmic and power law
dependence of the average charged particle multiplicity () on \sqrt(s),
and their extrapolation to energies accessible at LHC give very different
values. Assuming a reasonably good description of inclusive charged particle
multiplicity distributions by Negative Binomial Distributions (NBD) at lower
\sqrt(s) to hold for LHC energies, we observe that the logarithmic \sqrt(s)
dependence of are favored by the models at midrapidity. The dN_ch/d\eta
versus \eta for the existing measurements are found to be reasonably well
described by a function with three parameters which accounts for the basic
features of the distribution, height at midrapidity, central rapidity plateau
and the higher rapidity fall-off. Extrapolation of these parameters as a
function of \sqrt(s) is used to predict the pseudorapidity distributions of
charged particles at LHC energies. dN_ch/d\eta calculations from PYTHIA and
PHOJET models are found to be lower compared to those obtained from the
extrapolated dN_ch/d\eta versus \eta distributions for a broad \eta range.Comment: 11 pages and 13 figures. Substantially revised and accepted for
publication in Journal of Physics
STAR results on medium properties and response of the medium to energetic partons
We report new STAR results on the consequences of highly energetic partons
propagating through the medium formed in heavy ion collisions using
correlations as an experimental probe. The recent results providing insights
about color factor effects and path length dependence of parton energy loss,
system size dependence of di-hadron fragmentation functions, conical emission
and ridge formation in heavy ion collisions are presented.Comment: STAR Plenary talk at QM2008. Manuscript for the Proceedings of Quark
Matter 2008, Jaipur, Indi