389 research outputs found
Is there more than one thermal source?
BRAHMS has the ability to study relativistic heavy ion collisions over a wide
range of pT and rapidity. This allows us to test whether thermal models can be
generalized to describe the rapidity dependence of particle ratios. This
appears to work with the baryo-chemical potential changing more rapidly than
the temperature. Using fits to BRAHMS data for the 5% most central Au+Au
collisions we are able to describe Xi and Omega ratios from other experiments.
This paper is dedicated to Julia Thompson who worked to bring South African
teachers into physics.Comment: 5 pages, 4 figures, proceedings for SQM04 conference, Cape Town South
Afric
Cavity spin optodynamics
The dynamics of a large quantum spin coupled parametrically to an optical
resonator is treated in analogy with the motion of a cantilever in cavity
optomechanics. New spin optodynamic phenonmena are predicted, such as
cavity-spin bistability, optodynamic spin-precession frequency shifts, coherent
amplification and damping of spin, and the spin optodynamic squeezing of light.Comment: 4 pages, 3 figure
Tunable Cavity Optomechanics with Ultracold Atoms
We present an atom-chip-based realization of quantum cavity optomechanics
with cold atoms localized within a Fabry-Perot cavity. Effective sub-wavelength
positioning of the atomic ensemble allows for tuning the linear and quadratic
optomechanical coupling parameters, varying the sensitivity to the displacement
and strain of a compressible gaseous cantilever. We observe effects of such
tuning on cavity optical nonlinearity and optomechanical frequency shifts,
providing their first characterization in the quadratic-coupling regime.Comment: 4 pages, 5 figure
High-flux beam source for cold, slow atoms or molecules
We demonstrate and characterize a high-flux beam source for cold, slow atoms
or molecules. The desired species is vaporized using laser ablation, then
cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed
by particles exiting a hole in the buffer gas cell. We characterize the
properties of the beam (flux, forward velocity, temperature) for both an atom
(Na) and a molecule (PbO) under varying buffer gas density, and discuss
conditions for optimizing these beam parameters. Our source compares favorably
to existing techniques of beam formation, for a variety of applications.Comment: 5 Pages, 4 figure
CGC, QCD Saturation and RHIC data (Kharzeev-Levin-McLerran-Nardi point of view)
This is the talk given at the Workshop:"Focus on Multiplicitioes", Bari,
Italy, 17-19 June,2004.. In this talk, we are going to discuss ion-ion and
deuteron - nucleus RHIC data and show that they support, if not more, the idea
of the new QCD phase: colour glass condensate with saturated parton density. .Comment: 26 pages with 33 figure
Relativistic hydrodynamics with strangeness production
The relativistic hydrodynamic approach is used to describe production of
strangeness and/or heavy quarks in ultrarelativistic heavy ion reactions.
Production processes are important ingredients of dissipative effects in the
hadronic liquid. Beyond viscosity also chemo- and thermo-diffusion processes
are considered. This also allows to specify chemical and thermal freeze-out
conditions.Comment: v.2 with minor editorial corrections, 7 pages, talk given on the
SQM2007 conference, Levoca, June 24-29, 2007. To appear in the proceceeding:
Journal of Physics
Elliptical Flow in Relativistic Ion Collisions at s^(1/2)= 200 A GeV
A consistent picture of the Au+Au and D+Au, s^1/2 = 200 A GeV measurements at
RHIC obtained with the PHENIX, STAR, PHOBOS and BRAHMS detectors including both
the rapidity and transverse momentum spectra was previously developed with the
simulation LUCIFER. The approach was modeled on the early production of a fluid
of pre-hadrons after the completion of an initial, phase of high energy
interactions. The formation of pre-hadrons is discussed here, in a perturbative
QCD approach as advocated by Kopeliovich, Nemchik and Schmidt. In the second
phase of LUCIFER, a considerably lower energy hadron-like cascade ensues. Since
the dominant collisions occurring in this latter phase are meson-meson in
character while the initial collisions are between baryons, i.e. both involve
hadron sized interaction cross-sections, there is good reason to suspect that
the observed elliptical flow will be produced naturally, and this is indeed
found to be the case.Comment: 7 pages, 6 figure
Correlations and fluctuations studied with ALICE
The measurement of particle correlations and event-by-event fluctuations of
physical observables allows to study a large variety of properties of the
matter produced in ultra relativistic heavy-ion collisions. We will present
results for two-particle correlations, mean transverse momentum fluctuations,
and net charge fluctuations in Pb-Pb collisions at 2.76 TeV.Comment: 7 pages, 5 figures, Proceedings submitted for the 28th Winter
Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 2012; corrected typo
Suppression of High Transverse Momentum Spectra in Au+Au Collisions at RHIC
Au+Au, A GeV measurements at RHIC, obtained with the PHENIX,
STAR, PHOBOS and BRAHMS detectors, have all indicated a suppression of neutral
pion production, relative to an appropriately normalized NN level. For central
collisions and vanishing pseudo-rapidity these experiments exhibit suppression
in charged meson production, especially at medium to large transverse momenta.
In the PHENIX experiment similar behavior has been reported for
spectra.
In a recent work on the simpler D+Au interaction, to be considered perhaps as
a tune-up for Au+Au, we reported on a pre-hadronic cascade mechanism which
explains the mixed observation of moderately reduced suppression at
higher pseudo-rapidity as well as the Cronin enhancement at mid-rapidity. Here
we present the extension of this work to the more massive ion-ion collisions.
Our major thesis is that much of the suppression is generated in a late stage
cascade of colourless pre-hadrons produced after an initial short-lived
coloured phase. We present a pQCD argument to justify this approach and to
estimate the time duration of this initial phase. Of essential
importance is the brevity in time of the coloured phase existence relative to
that of the strongly interacting pre-hadron phase. The split into two phases is
of course not sharp in time, but adequate for treating the suppression of
moderate and high mesons.Comment: 19 pages, 10 figure
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