2,619 research outputs found
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
The chemical equilibration volume: measuring the degree of thermalization
We address the issue of the degree of equilibrium achieved in a high energy
heavy-ion collision. Specifically, we explore the consequences of incomplete
strangeness chemical equilibrium. This is achieved over a volume V of the order
of the strangeness correlation length and is assumed to be smaller than the
freeze-out volume. Probability distributions of strange hadrons emanating from
the system are computed for varying sizes of V and simple experimental
observables based on these are proposed. Measurements of such observables may
be used to estimate V and as a result the degree of strangeness chemical
equilibration achieved. This sets a lower bound on the degree of kinetic
equilibrium. We also point out that a determination of two-body correlations or
second moments of the distributions are not sufficient for this estimation.Comment: 16 pages, 15 figures, revtex
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.
Strange Particle Production from SIS to LHC
>1A review of meson emission in heavy ion collisions at incident energies
from SIS up to collider energies is presented. A statistical model assuming
chemical equilibrium and local strangeness conservation (i.e. strangeness
conservation per collision) explains most of the observed features.
Emphasis is put onto the study of and emission at low incident
energies. In the framework of this statistical model it is shown that the
experimentally observed equality of and rates at
``threshold-corrected'' energies is due to a
crossing of two excitation functions. Furthermore, the independence of the
to ratio on the number of participating nucleons observed between
SIS and RHIC is consistent with this model.
It is demonstrated that the production at SIS energies occurs
predominantly via strangeness exchange and this channel is approaching chemical
equilibrium. The observed maximum in the excitation function is
also seen in the ratio of strange to non-strange particle production. The
appearance of this maximum around 30 GeV is due to the energy
dependence of the chemical freeze-out parameters and .Comment: Presented at the International Workshop "On the Physics of the
Quark-Gluon Plasma", Palaiseau, France, September 2001. 10 pages, 8 figure
Z0 Boson Measurement with the ALICE Central Barrel in pp collisions at 14 TeV
The possibility to detect the Z0 in the ALICE central barrel is studied via
the electronic decay channel Z0->e+e-. The signal and the background are
simulated with the leading order event generator PYTHIA 6. The total
cross-sections are taken from NLO calculations. Based on test beam data, the
electron identification performance of the Transition Radiation Detector is
extrapolated to high momenta. The expected yields for minimum-bias pp
collisions at 14 TeV are presented. An isolation cut on the single electron,
together with a minimum transverse momentum cut, allows to obtain a clear
signal. The expected background is of the order of 1 % with the main
contribution coming from misidentified pions from jets.Comment: 4 pages, 3 figures, QM2008 proceeding
Pion Propagation near the QCD Chiral Phase Transition
We point out that, in analogy with spin waves in antiferromagnets, all
parameters describing the real-time propagation of soft pions at temperatures
below the QCD chiral phase transition can be expressed in terms of static
correlators. This allows, in principle, the determination of the soft pion
dispersion relation on the lattice. Using scaling and universality arguments,
we determine the critical behavior of the parameters of pion propagation. We
predict that when the critical temperature is approached from below, the pole
mass of the pion drops despite the growth of the pion screening mass. This fact
is attributed to the decrease of the pion velocity near the phase transition.Comment: 8 pages (single column), RevTeX; added references, version to be
published in PR
Overpopulation of in pp collisions: a way to distinguish statistical hadronization from string dynamics
The ratio originating from string decays is predicted
to be larger than unity in proton proton interactions at SPS energies (=160 GeV). The anti-omega dominance increases with decreasing beam energy.
This surprising behavior is caused by the combinatorics of quark-antiquark
production in small and low-mass strings. Since this behavior is not found in a
statistical description of hadron production in proton proton collisions, it
may serve as a key observable to probe the hadronization mechanism in such
collisions.Comment: 4 pages, 4 figure
Particle Ratios, Equilibration, and the QCD Phase Boundary
We discuss the status of thermal model descriptions of particle ratios in
central nucleus-nucleus collisions at ultra-relativistic energy. An alternative
to the
``Cleymans-Redlich'' interpretation of the freeze-out trajectory is given in
terms of the total baryon density. Emphasis is placed on the relation between
the chemical equilibration parameters and the QCD phase boundary. Furthermore,
we trace the essential difference between thermal model analyses of data from
collisions between elementary particles and from heavy ion collisions as due to
a transition from local strangeness conservation to percolation of strangeness
over large volumes, as occurs naturally in a deconfined medium.
We also discuss predictions of the thermal model for composite particle
production.Comment: Contribution to SQM2001 Conference, submitted to J. Phys.
Finite hadronization time and unitarity in quark recombination model
The effect of finite hadronization time is considered in the recombination
model, and it is shown that the hadron multiplicity turns out to be
proportional to the initial quark density and unitarity is conserved in the
model. The baryon to meson ratio increases rapidly with the initial quark
density due to competition among different channels.Comment: 4 pages in RevTeX, 3 eps figures, to appear in J. Phys.G as a lette
Distinguishing Hadronic Cascades from Hydrodynamic Models in Pb(160 AGeV)+Pb Reactions by Impact Parameter Variation
We propose to study the impact parameter dependence of the
anti-Lambda/anti-Proton ratio in Pb(160AGeV)+Pb reactions. The
anti-Lambda/anti-Proton ratio is a sensible tool to distinguish between
hadronic cascade models and hydrodynamical models, which incorporate a QGP
phase transition
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