2,844 research outputs found
Production of Strange Clusters and Strange Matter in Nucleus-Nucleus Collisions at the AGS
Production probabilities for strange clusters and strange matter in Au+Au
collisions at AGS energy are obtained in the thermal fireball model. The only
parameters of the model, the baryon chemical potential and temperature, were
determined from a description of the rather complete set of hadron yields from
Si+nucleus collisions at the AGS. For the production of light nuclear fragments
and strange clusters the results are similar to recent coalescence model
calculations. Strange matter production with baryon number larger than 10 is
predicted to be much smaller than any current experimental sensitivities.Comment: 9 Pages (no figures
Production of strange particles at intermediate pT at RHIC
The recombination model is applied to the production of
and at all in central Au+Au collisions. The thermal-shower
component of the recombination is found to be important for and ,
but only in a minor way for and in the intermediate to high
region. The normalization and inverse slope of the thermal partons in the
strange sector are determined by fitting the low- data. At higher
the data of and in the log scale are all well
reproduced in our study that extends the thermal contribution and includes the
shower contribution. The calculated result on the ratio rises to a
maximum of around 2 at GeV/c, arching over the data in linear
scale. The production of and are shown to arise mainly from the
recombination of thermal partons, thus exhibiting exponential dependences
in agreement with the data. Their ratio, , rises linearly to
GeV/c and develops a maximum at GeV/c. It is
argued that the spectra of and reveal directly the
partonic nature of the thermal source that characterizes quark-gluon plasma.
Comments are made on the puzzle due to the simultaneous observation of
both the exponential behavior of the spectrum in and the
existence of low- particles associated with as trigger.Comment: Revised manuscript with new figure
On the Energy and Centrality Dependence of Higher Order Moments of Net-Proton Distributions in Relativistic Heavy Ion Collisions
The higher order moments of the net-baryon distributions in relativistic
heavy ion collisions are useful probes for the QCD critical point and
fluctuations. Within a simple model we study the colliding energy and
centrality dependence of the net-proton distributions in the central rapidity
region. The model is based on considering the baryon stopping and pair
production effects in the processes. Based on some physical reasoning, the
dependence is parameterized. Predictions for the net-proton distributions for
Au+Au and Pb+Pb collisions at different centralities at =39 and
2760 GeV, respectively, are presented from the parameterizations for the model
parameters. A possible test of our model is proposed from investigating the net
proton distributions in the non-central rapidity region for different colliding
centralities and energies.Comment: 6 pages in revtex4, 8 eps figures. arXiv admin note: text overlap
with arXiv:1107.474
Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies
Measurements of open charm hadro-production from CERN and Fermilab
experiments are reviewed, with particular emphasis on the absolute cross
sections and on their A and sqrt(s) dependences. Differential pt and xf cross
sections calculated with the Pythia event generator are found to be in
reasonable agreement with recent data. The calculations are scaled to
nucleus-nucleus collisions and the expected lepton pair yield is deduced. The
charm contribution to the low mass dilepton continuum observed by the CERES
experiment is found to be negligible. In particular, it is shown that the
observed low mass dilepton excess in S-Au collisions cannot be explained by
charm enhancement.Comment: 19 pages, 12 eps figures included. To be published in Z.Phys.
and production in Au+Au collisions at = 130 and 200 GeV
Mid-rapidity Omega and anti-Omega production in Au+Au collisions at RHIC is
studied with the STAR experiment. We report preliminary results on yields and
spectra at = 130 and 200 GeV. Production relative to negatively
charged hadrons (h-) as well as thermal freeze-out and collective expansion are
discussed.Comment: 4 pages, 5 figures, 1 table, Contribution to Quark Matter 2002,
Nantes, France, July 200
Drift velocity and gain in argon- and xenon-based mixtures
We present measurements of drift velocities and gains in gas mixtures based
on Ar and Xe, with CO2, CH4, and N2 as quenchers, and compare them with
calculations. In particular, we show the dependence of Ar- and Xe-CO2 drift
velocities and gains on the amount of nitrogen contamination in the gas, which
in real experiments may build up through leaks. A quantification of the Penning
mechanism which contributes to the Townsend coefficients of a given gas mixture
is proposed.Comment: 11 pages, 7 figures, accepted for publication in Nucl.Instrum.Meth.
A. Data files available at http://www-alice.gsi.de/tr
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
Recombination of Shower Partons at High in Heavy-Ion Collisions
A formalism for hadron production at high \pt in heavy-ion collisions has
been developed such that all partons hadronize by recombination. The
fragmentation of a hard parton is accounted for by the recombination of shower
partons that it creates. Such shower partons can also recombine with the
thermal partons to form particles that dominate over all other possible modes
of hadronization in the GeV range. The results for the high \pt
spectra of pion, kaon, and proton agree well with experiments. Energy loss of
partons in the dense medium is taken into account on the average by an
effective parameter by fitting data, and is found to be universal independent
of the type of particles produced, as it should. Due to the recombination of
thermal and shower partons, the structure of jets produced in nuclear
collisions is different from that in collisions. The consequence on
same-side correlations is discussed.Comment: This revised version contains minor changes and a new figure
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
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