1,282 research outputs found
A model for the spacetime evolution of heavy-ion collisions at RHIC
We investigate the space-time evolution of ultrarelativistic Au-Au collisions
at full RHIC energy using a schematic model of the expansion. Assuming a
thermally equilibrated system, we can adjust the essential scale parameters of
this model such that the measured transverse momentum spectra and Hanbury-Brown
Twiss (HBT) correlation parameters are well described. We find that the
experimental data strongly constrain the dynamics of the evolution of the
emission source although hadronic observables for the most part reflect the
final breakup of the system.Comment: 9 pages, 3 figures, submitted to Phys. Rev.
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
Why a long-lived fireball can be compatible with HBT measurements
The common interpretation of HBT data measured at top SPS energies leads to
apparent source lifetimes of 6-8 fm/c and emission duration of approximately
2-3 fm/c. We investigate a scenario with continuous pion emission from a
long-lived (~17 fm/c) thermalized source in order to show that it is not
excluded by the data. Starting from a description of the source's spacetime
expansion based on gross thermodynamical properties of hot matter (which is
able to describe a number of experimental observables), we introduce the pion
emission function with a contribution from continuous emission during the
source's lifetime and another contribution from the final breakup and proceed
by calculating the HBT parameters R_out and R_side. The results are compared
with experimental data measured at SPS for 158 AGeV central Pb-Pb collisions.
We achieve agreement with data, provided that some minor modifications of the
fireball evolution scenario are made and find that the parameter R_out is not
sensitive to the fireball lifetime, but only to the duration of the final
breakup, in spite of the fact that emission takes place throughout the whole
lifetime. We explicitly demonstrate that those findings do not alter previous
results obtained within this model.Comment: 13 pages, 5 figures, submitted to Phys. Rev. C. (revised description
of fireball expansion
Photonic measurements of the longitudinal expansion dynamics in Heavy-Ion collisions
Due to the smallness of the electromagnetic coupling, photons escape from the
hot and dense matter created in an heavy-ion collision at all times, in
contrast to hadrons which are predominantly emitted in the final freeze-out
phase of the evolving system. Thus, the thermal photon yield carries an imprint
from the early evolution. We suggest how this fact can be used to gain
information about where between the two limiting cases of Bjorken
(boost-invariant expansion) and Landau (complete initial stopping and
re-expansion) hydrodynamics the actual evolution can be found. We argue that
both the rapidity dependence of the photon yield and photonic HBT radii are
capable of answering this question.Comment: 10 pages, 3 figure
What does the rho-meson do? In-medium mass shift scenarios versus hadronic model calculations
The NA60 experiment has studied low-mass muon pair production in In-In
collisions at with unprecedented precision. With these results
there is hope that the in-medium modifications of the vector meson spectral
function can be constrained more thoroughly than before. We investigate in
particular what can be learned about collisional broadening by a hot and dense
medium and what constrains the experimental results put on in-medium mass shift
scenarios. The data show a clear indication of considerable in-medium
broadening effects but disfavor mass shift scenarios where the -meson
mass scales with the square root of the chiral condensate. Scaling scenarios
which predict at finite density a dropping of the -meson mass that is
stronger than that of the quark condensate are clearly ruled out since they are
also accompanied by a sharpening of the spectral function.Comment: Proceeding contribution, Talk given by J. Ruppert at Workshop for
Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus
Collisions (Hot Quarks 2006), Villasimius, Sardinia, Italy, 15-20 May 2006.
To appear in EPJ
A comprehensive description of multiple observables in heavy-ion collisions at SPS
Combining and expanding on work from previous publications, a model for the
evolution of ultrarelativistic heavy-ion collisions at the CERN SPS for 158
AGeV beam energy is presented. Based on the assumption of thermalization and a
parametrization of the space-time expansion of the produced matter, this model
is able to describe a large set of observables including hadronic momentum
spectra, correlations and abundancies, the emission of real photons, dilepton
radiation and the suppression pattern of charmonia. Each of these obervables
provides unique capabilities to study the reaction dynamics and taken together
they form a strong and consistent picture of the evolving system. Based on the
emission of hard photons, we argue that a strongly interacting, hot and dense
system with temperatures above 250 MeV has to be created early in the reaction.
Such a system is bound to be different from hadronic matter and likely to be a
quark-gluon plasma, and we find that this assumption is in line with the
subsequent evolution of the system that is reflected in other observables.Comment: 21 pages, 10 figures, submitted to J. Phys.
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
Comparing different freeze-out scenarios in azimuthal hadron correlations induced by fast partons
I review the linearized hydrodynamical treatment of a fast parton traversing
a perturbative quark-gluon plasma. Using numerical solutions for the medium's
response to the fast parton, I obtain the medium's distribution function which
is then used in a Cooper-Frye freeze-out prescription to obtain an azimuthal
particle spectrum. Two different freeze-out scenarios are considered which
yield significantly different results. I conclude that any meaningful
comparison of azimuthal hadron correlation functions to RHIC data requires
implementing a realistic freeze-out scenario in an expanding medium.Comment: Contribution to the Proceedings for 2008 Hot Quarks in Estes Park,
CO, as accepted for publication in EPJ-
Naturally Occurring Organic Compounds in Eutrophic Hyrum Reservoir, Utah
Methods of collecting, concentrating, separating, and identifying organic compounds in natural water systems were studied. The most appropriate methods were applied to a eutrophic reservoir (Hyrum Reservoir, Utah) and resulted in the identification of 27 volatile, organic compounds: Alcohols
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