1,230 research outputs found
Collision centrality and dependence of the emission of thermal photons from fluctuating initial state in ideal hydrodynamic calculation
Fluctuations in the initial QCD matter density distribution are found to
enhance the production of thermal photons significantly in the range 2 \leq pT
\leq 4 GeV/c compared to a smooth initial state averaged profile in ideal
hydrodynamic calculation for 200 AGeV Au+Au collisions at the Relativistic
Heavy Ion Collider (RHIC) and 2.76 ATeV Pb+Pb collisions at the Large Hadron
Collider (LHC). The thermal emission of photons is strongly dependent on the
initial temperature of the system where the presence of 'hotspots' in the
initial state translates into enhanced production of photons compared to a
smooth profile. The effect of fluctuations in the initial state is found to be
stronger for peripheral collisions and for lower beam energies. The pT spectra
are found to be quite sensitive to the value of the initial formation time of
the plasma which is not known unambiguously and which may vary with collision
centralities at a particular beam energy. Increase in the value of the
formation time lowers the production of thermal photons compared to the results
from a shorter formation time. However, the relative enhancement from
fluctuating initial tates (compared to a smooth initial state) is found to be
stronger for the larger values of formation time. The pT spectra alone are
found to be insufficient to quantify the fluctuations in the initial density
distribution due to the uncertainties in the initial conditions. A suitably
normalized ratio of central-to-peripheral yield as a function of collision
centrality and pT can be a useful measure of the fluctuation size scale.Comment: 10 pages, 10 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.
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-
Interpretation of Recent SPS Dilepton Data
We summarize our current theoretical understanding of in-medium properties of
the electromagnetic current correlator in view of recent dimuon data from the
NA60 experiment in In(158 AGeV)-In collisions at the CERN-SPS. We discuss the
sensitivity of the results to space-time evolution models for the hot and dense
partonic and hadronic medium created in relativistic heavy-ion collisions and
the contributions from different sources to the dilepton-excess spectra.Comment: To appear in the proceedings of the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006) v2:
references added, minor typos correcte
Deciphering the properties of the medium produced in heavy ion collisions at RHIC by a pQCD analysis of quenched large spectra
We discuss the question of the relevance of perturbative QCD calculations for
analyzing the properties of the dense medium produced in heavy ion collisions.
Up to now leading order perturbative estimates have been worked out and
confronted with data for quenched large hadron spectra. Some of
them are giving paradoxical results, contradicting the perturbative framework
and leading to speculations such as the formation of a strongly interacting
quark-gluon plasma. Trying to bypass some drawbacks of these leading order
analysis and without performing detailed numerical investigations, we collect
evidence in favour of a consistent description of quenching and of the
characteristics of the produced medium within the pQCD framework.Comment: 10 pages, 3 figure
Refined Mission Analysis for Heracles - a Robotic Lunar Surface Sample Return Mission Utilizing Human Infrastructure
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