2,888 research outputs found
Chemical Equilibration in Hadronic Collisions
We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma
using the first principles method of QCD effective kinetic theory, accurate at
weak coupling. In longitudinally expanding systems--relevant for relativistic
nuclear collisions--we find that for realistic couplings chemical equilibration
takes place after hydrodynamization, but well before local thermalization. We
estimate that hadronic collisions with final state multiplicities
live long enough to reach approximate
chemical equilibrium, which is consistent with the saturation of strangeness
enhancement observed in proton-proton, proton-nucleus and nucleus-nucleus
collisions.Comment: 7 pages, 3 figures, see also our companion paper arXiv:1811.03068, v2
small changes, published versio
Formation of charmonium states in heavy ion collisions and thermalization of charm
We examine the possibility to utilize in-medium charmonium formation in heavy
ion interactions at collider energy as a probe of the properties of the medium.
This is possible because the formation process involves recombination of charm
quarks which imprints a signal on the resulting normalized transverse momentum
distribution containing information about the momentum distribution of the
quarks. We have contrasted the transverse momentum spectra of J/Psi,
characterized by , which result from the formation process in which the
charm quark distributions are taken at opposite limits with regard to
thermalization in the medium. The first uses charm quark distributions
unchanged from their initial production in a pQCD process, appropriate if their
interaction with the medium is negligible. The second uses charm quark
distributions which are in complete thermal equilibrium with the transversely
expanding medium, appropriate if a very strong interaction between charm quarks
and medium exists. We find that the resulting of the formed J/Psi
should allow one to differentiate between these extremes, and that this
differentiation is not sensitive to variations in the detailed dynamics of
in-medium formation. We include a comparison of predictions of this model with
preliminary PHENIX measurements, which indicates compatibility with a
substantial fraction of in-medium formation.Comment: 8 pages, 5 figures, based on presentation at the Workshop on
Quark-Gluon-Plasma Thermalization (QGPTH05), Vienna, Austria, August 10-12,
2005. To be published in the proceedings. Two figures and 3 references
update
The canonical partition function for relativistic hadron gases
Particle production in high-energy collisions is often addressed within the
framework of the thermal (statistical) model. We present a method to calculate
the canonical partition function for the hadron resonance gas with exact
conservation of the baryon number, strangeness, electric charge, charmness and
bottomness. We derive an analytical expression for the partition function which
is represented as series of Bessel functions. Our results can be used directly
to analyze particle production yields in elementary and in heavy ion
collisions. We also quantify the importance of quantum statistics in the
calculations of the light particle multiplicities in the canonical thermal
model of the hadron resonance gas.Comment: 10 pages, 2 figures; submitted for publication in EPJ
A large- PNJL model with explicit Z symmetry
A PNJL model is built, in which the Polyakov-loop potential is explicitly
Z-symmetric in order to mimic a Yang-Mills theory with gauge group
SU(). The physically expected large- and large- behaviours of the
thermodynamic observables computed from the Polyakov-loop potential are used to
constrain its free parameters. The effective potential is eventually
U(1)-symmetric when is infinite. Light quark flavours are added by using
a Nambu-Jona-Lasinio (NJL) model coupled to the Polyakov loop (the PNJL model),
and the different phases of the resulting PNJL model are discussed in 't
Hooft's large- limit. Three phases are found, in agreement with previous
large- studies. When the temperature is larger than some deconfinement
temperature , the system is in a deconfined, chirally symmetric, phase for
any quark chemical potential . When however, the system is in a
confined phase in which chiral symmetry is either broken or not. The critical
line , signalling the restoration of chiral symmetry, has the same
qualitative features than what can be obtained within a standard PNJL
model.Comment: To appear in Phys Rev
The thermal model on the verge of the ultimate test: particle production in Pb-Pb collisions at the LHC
We investigate the production of hadrons in nuclear collisions within the
framework of the thermal (or statistical hadronization) model. We discuss both
the ligh-quark hadrons as well as charmonium and provide predictions for the
LHC energy. Even as its exact magnitude is dependent on the charm production
cross section, not yet measured in Pb-Pb collisions, we can confidently predict
that at the LHC the nuclear modification factor of charmonium as a function of
centrality is larger than that observed at RHIC and compare the experimental
results to these predictions.Comment: 4 pages, 3 figures; proceedings of QM201
Charmonium suppression at RHIC and SPS: a hadronic baseline
A kinetic equation approach is applied to model anomalous J/psi suppression
at RHIC and SPS by absorption in a hadron resonance gas which successfully
describes statistical hadron production in both experiments. The puzzling
rapidity dependence of the PHENIX data is reproduced as a geometric effect due
to a longer absorption path for J/psi production at forward rapidity.Comment: 16 pages, 6 figures, final version accepted for publication in Phys.
Lett.
Quarkonium formation in statistical and kinetic models
I review the present status of two related models addressing scenarios in
which the formation of heavy quarkonium states in high energy heavy ion
collisions proceed via "off-diagonal" combinations of a quark and an antiquark.
The physical process involved belongs to a general class of quark
"recombination", although technically the recombining quarks here were never
previously bound in a quarkonium state. Features of these processes relevant as
a signature of color deconfinement are discussed.Comment: 6 pages, 8 figures, based on invited plenary talk at Hard Probes
2004, Ericeira, Portugal, November 3-11, 2004, to appear in the proceeding
Position Reconstruction in Drift Chambers operated with Xe, CO2 (15%)
We present measurements of position and angular resolution of drift chambers
operated with a Xe,CO(15%) mixture. The results are compared to Monte Carlo
simulations and important systematic effects, in particular the dispersive
nature of the absorption of transition radiation and non-linearities, are
discussed. The measurements were carried out with prototype drift chambers of
the ALICE Transition Radiation Detector, but our findings can be generalized to
other drift chambers with similar geometry, where the electron drift is
perpendicular to the wire planes.Comment: 30 pages, 18 figure
Heavy quark(onium) at LHC: the statistical hadronization case
We discuss the production of charmonium in nuclear collisions within the
framework of the statistical hadronization model. We demonstrate that the model
reproduces very well the availble data at RHIC. We provide predictions for the
LHC energy where, dependently on the charm production cross section, a
dramatically different behaviour of charmonium production as a function of
centrality might be expected. We discuss also the case in elementary
collisions, where clearly the statistical model does not reproduce the
measurements.Comment: 8 pages, 5 figures; proceeding of SQM09, Buzios, Brazil, to be
published in J. Phys.
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