451 research outputs found
Statistical description with anisotropic momentum distributions for hadron production in nucleus-nucleus collisions
The various experimental data at AGS, SPS and RHIC energies on hadron
particle yields for central heavy ion collisions are investigated by employing
a generalized statistical density operator, that allows for a well-defined
anisotropic local momentum distribution for each particle species, specified by
a common streaming velocity parameter. The individual particle ratios are
rather insensitive to a change in this new intensive parameter. This leads to
the conclusion that the reproduction of particle ratios by a statistical
treatment does not imply the existence of a fully isotropic local momentum
distribution at hadrochemical freeze-out, i.e. a state of almost complete
thermal equilibrium.Comment: 14 pages, revtex, 3 figures accepted version, to be published in
Journal of Physics
Dijet asymmetry at the Large Hadron Collider
The MARTINI numerical simulation allows for direct comparison of theoretical
model calculations and the latest results for dijet asymmetry from the ATLAS
and CMS collaborations. In this paper, partons are simulated as undergoing
radiative and collisional processes throughout the evolution of central
lead-lead collisions at the Large Hadron Collider. Using hydrodynamical
background evolution determined by a simulation which fits well with the data
on charged particle multiplicities from ALICE and a value of , the dijet asymmetry is found to be consistent with partonic energy
loss in a hot, strongly-interacting medium.Comment: 8 pages, 3 figures. For version 2: ATLAS' latest analysis is
included, with some comments and minor changes of wordin
Hard dihadron correlations in heavy-ion collisions at RHIC and LHC
High transverse momentum (P_T) processes are considered to be an important
tool to probe and understand the medium produced in ultrarelativistic heavy-ion
collisions via the interaction of hard, perturbatively produced partons with
the medium. In this context, triggered hard dihadron correlations constitute a
class of observables set between hard single inclusive hadrons (dominated by
the leading jet fragments) and fully reconstructed jets - while they probe some
features of the perturbative QCD evolution of a parton shower in the medium,
they do not suffer from the problem of finding a suitable separation between
soft perturbative (jet-like) and soft non-perturbative (medium-like) physics as
the identification of full jets does. On the other hand, the trigger
requirement introduces non-trivial complications to the process, which makes
the medium-modification of the correlation pattern difficult and non-intuitive
to understand. In this work, we review the basic physics underlying triggered
dihadron correlations and make a systematic comparison of several combinations
of medium evolution and parton-medium interaction models with the available
data from 200 AGeV Au-Au collisions at RHIC. We also discuss the expected
results for 2.76 ATeV Pb-Pb collisions at the LHC.Comment: 13 pages, 7 figures, submitted to PR
Energy loss in a fluctuating hydrodynamical background
Recently it has become apparent that event-by-event fluctuations in the
initial state of hydrodynamical modelling of ultrarelativistic heavy-ion
collisions are crucial in order to understand the full centrality dependence of
the elliptic flow coefficient v_2. In particular, in central collisions the
density fluctuations play a major role in generating the spatial eccentricity
in the initial state. This raises the question to what degree high P_T physics,
in particular leading-parton energy loss, which takes place in the background
of an evolving medium, is sensitive to the presence of the event-by-event
density fluctuations in the background. In this work, we report results for the
effects of fluctuations on the nuclear modification factor R_AA in both central
and noncentral sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC. Two different
types of energy-loss models, a radiative and an elastic, are considered. In
particular, we study the dependence of the results on the assumed spatial size
of the density fluctuations, and discuss the angular modulation of R_AA with
respect to the event plane.Comment: 9 pages, 9 figure
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