8 research outputs found
Particle yield fluctuations and chemical non-equilibrium at RHIC
We study charge fluctuations within the statistical hadronization model.
Considering both the particle yield ratios and the charge fluctuations we show
that it is possible to differentiate between chemical equilibrium and
non-equilibrium freeze-out conditions. As an example of the procedure we show
quantitatively how the relative yield ratio together with the
normalized net charge fluctuation v(Q)=\ave{\Delta Q^2}/\ave{\Nch} constrain
the chemical conditions at freeze-out. We also discuss the influence of the
limited detector acceptance on fluctuation measurements, and show how this can
be accounted for within a quantitative analysis.Comment: Accepted for publication by Physical Review
Resonances and fluctuations of strange particle in 200 GeV Au-Au collisions
We perform an analysis of preliminary data on strange particles yields and
fluctuations within the Statistical hadronization model. We begin by describing
the theoretical disagreements between different statistical models currently on
the market. We then show how the simultaneous analysis of yields and
fluctuations can be used to differentiate between the different models, and
determine if one of them can be connected to underlying physics. We perform a
study on a RHIC 200 GeV data sample that includes stable particles, resonances,
and the event-by-event fluctuation of the ratio. We show that the
equilibrium statistical model can not describe the fluctuation, unless an
unrealistically small volume is assumed. Such small volume then makes it
impossible to describe the total particle multiplicity. The non-equilibrium
model,on the other hand, describes both the fluctuation and yields
acceptably due to the extra boost to the fluctuation provided by the high
pion chemical potential. and abundance is described
within error bars, but the is under-predicted to 1.5 standard
deviations. We suggest further measurements that have the potential to test the
non-equilibrium model, as well as gauge the effect of re-interactions between
hadronization and freeze-out.Comment: References added, equations corrected. As accepted for publication by
Journal of Physics
Resonances and fluctuations at SPS and RHIC
We perform an analysis of preliminary data on hadron yields and fluctuations
within the Statistical hadronization ansatz. We describe the theoretical
disagreements between different statistical models currently on the market, and
show how the simultaneous analysis of yields and fluctuations can be used to
determine if one of them can be connected to underlying physics. We perform
such an analysis on preliminary RHIC and SPS A-A data that includes particle
yields, ratios and event by event fluctuations. We show that the equilibrium
statistical model can not describe the fluctuation measured at RHIC and
SPS, unless an unrealistically small volume is assumed. Such small volume then
makes it impossible to describe the total particle multiplicity. The
non-equilibrium model,on the other hand, describes both the fluctuation
and yields acceptably due to the extra boost to the fluctuation provided
by the high pion chemical potential. We show, however, that both models
significantly over-estimate the fluctuation measured at the SPS, and
speculate for the reason behind this.Comment: Presented at Hot Quarks, 2006 In press, European Physical Journal
Thermal Dileptons at LHC
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb
collisions at LHC. Hadronic emission in the low-mass region is calculated using
in-medium spectral functions of light vector mesons within hadronic many-body
theory. In the intermediate-mass region thermal radiation from the Quark-Gluon
Plasma, evaluated perturbatively with hard-thermal loop corrections, takes
over. An important source over the entire mass range are decays of correlated
open-charm hadrons, rendering the nuclear modification of charm and bottom
spectra a critical ingredient.Comment: 2 pages, 2 figures, contributed to Workshop on Heavy Ion Collisions
at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun
2007 v2: acknowledgment include
Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
We review the most important experimental results from the first three years
of nucleus-nucleus collision studies at RHIC, with emphasis on results from the
STAR experiment, and we assess their interpretation and comparison to theory.
The theory-experiment comparison suggests that central Au+Au collisions at RHIC
produce dense, rapidly thermalizing matter characterized by: (1) initial energy
densities above the critical values predicted by lattice QCD for establishment
of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by
constituent interactions of very short mean free path, established most
probably at a stage preceding hadron formation; and (3) opacity to jets. Many
of the observations are consistent with models incorporating QGP formation in
the early collision stages, and have not found ready explanation in a hadronic
framework. However, the measurements themselves do not yet establish
unequivocal evidence for a transition to this new form of matter. The
theoretical treatment of the collision evolution, despite impressive successes,
invokes a suite of distinct models, degrees of freedom and assumptions of as
yet unknown quantitative consequence. We pose a set of important open
questions, and suggest additional measurements, at least some of which should
be addressed in order to establish a compelling basis to conclude definitively
that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.
Heavy-ion collisions at the LHC - Last call for predictions
This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.This is a manuscript of an article from Journal of Physics G 35 (2008): 054001, doi: 10.1088/0954-3899/35/5/054001. Posted with permission.</p