4,592 research outputs found
critRHIC: The RHIC Low Energy Program
Recent experimental and theoretical developments have motivated interest in a
more detailed exploration of heavy ion collisions in the range sqrt(sNN)=5-15
GeV. In contrast to interactions at the full RHIC energy of sqrt(sNN)=200 GeV,
such collisions result in systems characterized by much higher baryon chemical
potential, muB. Extensions of lattice QCD calculations to non-zero values of
muB suggest that a critical point may exist in this region of the QCD phase
diagram. Discovery of the critical point or, equivalently, determining the
location where the phase transition from partonic to hadronic matter switches
from a smooth crossover to 1st order would establish a major landmark in the
phase diagram. Initial studies of Pb+Pb collisions in this energy range have
revealed several unexpected features in the data. In response to these results,
it has been suggested that the existing RHIC accelerator and experiments can be
used to further the investigation of this important physics topic. This
proceeding briefly summarizes the theoretical and experimental situation with
particular emphasis on the conclusions from a RIKEN BNL workshop held in March
of 2006.Comment: 8 pages, 2 figures, Conference Proceeding from Strangeness in Quark
Matter 2006, accepted for publication in J. Phys. G; Added final journal
reference and fixed typo in Ref
Is Strangeness still interesting at RHIC ?
With the advent of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven
National Laboratory (BNL), Heavy Ion Physics will enter a new energy regime.
The question is whether the signatures proposed for the discovery of a phase
transition from hadronic matter to a Quark Gluon Plasma (QGP), that were
established on the basis of collisions at the BEVALAC, the AGS, and the SPS,
respectively, are still useful and detectable at these high incident energies.
In the past two decades, measurements related to strangeness formation in the
collision were advocated as potential signatures and were tested in numerous
fixed target experiments at the AGS and the SPS. In this article I will review
the capabilities of the RHIC detectors to measure various aspects of
strangeness, and I will try to answer the question whether the information
content of those measurements is comparable to the one at lower energies.Comment: 12 pages, 7 figures, Invited Talk at the IV International Conference
on Strangeness in Quark Matter, Padova (Italy), July 20-24, 199
Antihyperon-Production in Relativistic Heavy Ion Collision
Recently it has been shown that the observed antiproton yield in heavy-ion
collisions at CERN-SpS energies can be understood by multi-pionic interactions
which enforce local chemical equilibrium of the antiprotons with the nucleons
and pions. Here we show that antihyperons are driven towards local chemical
equilibrium with pions, nucleons and kaons on a timescale of less than 3 fm/c
when applying a similar argument for the antihyperons by considering the
inverse channel of annihilation reactions anti-Y + p to pions + kaons. These
multi-mesonic reactions easily explain the antihyperon yields at CERN-SpS
energies as advertised in pure thermal, hadronic models without the need of a
quark gluon plasma phase. In addition, the argument also applies for AGS
energies.Comment: 4 pages using RevTeX, 1 eps figur
Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies
Using the technique of quantum transport of the interfering pair we examine
the Hanbury-Brown-Twiss (HBT) interferometry signatures for the
particle-emitting sources of pions and kaons produced in the heavy ion
collisions at GSI-FAIR energies. The evolution of the sources is described by
relativistic hydrodynamics with the system equation of state of the first-order
phase transition from quark-gluon plasma (QGP) to hadronic matter. We use
quantum probability amplitudes in a path-integral formalism to calculate the
two-particle correlation functions, where the effects of particle decay and
multiple scattering are taken into consideration. We find that the HBT radii of
kaons are smaller than those of pions for the same initial conditions. Both the
HBT radii of pions and kaons increase with the system initial energy density.
The HBT lifetimes of the pion and kaon sources are sensitive to the initial
energy density. They are significantly prolonged when the initial energy
density is tuned to the phase boundary between the QGP and mixed phase. This
prolongations of the HBT lifetimes of pions and kaons may likely be observed in
the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure
Applicability of Monte Carlo Glauber models to relativistic heavy ion collision data
The accuracy of Monte Carlo Glauber model descriptions of minimum-bias
multiplicity frequency distributions is evaluated using data from the
Relativistic Heavy Ion Collider (RHIC) within the context of a sensitive,
power-law representation introduced previously by Trainor and Prindle (TP).
Uncertainties in the Glauber model input and in the mid-rapidity multiplicity
frequency distribution data are reviewed and estimated using the TP centrality
methodology. The resulting errors in model-dependent geometrical quantities
used to characterize heavy ion collisions ({\em i.e.} impact parameter, number
of nucleon participants , number of binary interactions ,
and average number of binary collisions per incident participant nucleon )
are presented for minimum-bias Au-Au collisions at = 20, 62,
130 and 200 GeV and Cu-Cu collisions at = 62 and 200 GeV.
Considerable improvement in the accuracy of collision geometry quantities is
obtained compared to previous Monte Carlo Glauber model studies, confirming the
TP conclusions. The present analysis provides a comprehensive list of the
sources of uncertainty and the resulting errors in the above geometrical
collision quantities as functions of centrality. The capability of energy
deposition data from trigger detectors to enable further improvements in the
accuracy of collision geometry quantities is also discussed.Comment: 27 pages, 4 figures, 11 table
The Importance of Correlations and Fluctuations on the Initial Source Eccentricity in High-Energy Nucleus-Nucleus Collisions
In this paper, we investigate various ways of defining the initial source
eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we
examine the participant eccentricity, which quantifies the eccentricity of the
initial source shape by the major axes of the ellipse formed by the interaction
points of the participating nucleons. We show that reasonable variation of the
density parameters in the Glauber calculation, as well as variations in how
matter production is modeled, do not significantly modify the already
established behavior of the participant eccentricity as a function of collision
centrality. Focusing on event-by-event fluctuations and correlations of the
distributions of participating nucleons we demonstrate that, depending on the
achieved event-plane resolution, fluctuations in the elliptic flow magnitude
lead to most measurements being sensitive to the root-mean-square, rather
than the mean of the distribution. Neglecting correlations among
participants, we derive analytical expressions for the participant eccentricity
cumulants as a function of the number of participating nucleons,
\Npart,keeping non-negligible contributions up to \ordof{1/\Npart^3}. We
find that the derived expressions yield the same results as obtained from
mixed-event MCG calculations which remove the correlations stemming from the
nuclear collision process. Most importantly, we conclude from the comparison
with MCG calculations that the fourth order participant eccentricity cumulant
does not approach the spatial anisotropy obtained assuming a smooth nuclear
matter distribution. In particular, for the Cu+Cu system, these quantities
deviate from each other by almost a factor of two over a wide range in
centrality.Comment: 18 pages, 10 figures, submitted to PR
Are we close to the QGP? - Hadrochemical vs. microscopic analysis of particle production in ultrarelativistic heavy ion collisions
Ratios of hadronic abundances are analyzed for pp and nucleus-nucleus
collisions at sqrt(s)=20 GeV using the microscopic transport model UrQMD.
Secondary interactions significantly change the primordial hadronic cocktail of
the system. A comparison to data shows a strong dependence on rapidity. Without
assuming thermal and chemical equilibrium, predicted hadron yields and ratios
agree with many of the data, the few observed discrepancies are discussed.Comment: 12 pages, 4 figure
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