8,899 research outputs found
Hydrogen-like Atoms from Ultrarelativistic Nuclear Collisions
The number of hydrogen-like atoms produced when heavy nuclei collide is
estimated for central collisions at the Relativistic Heavy Ion Collider using
the sudden approximation of Baym et al. As first suggested by Schwartz, a
simultaneous measurement of the hydrogen and hadron spectra will allow an
inference of the electron or muon spectra at low momentum where a direct
experimental measurement is not feasible.Comment: 6 pages, 4 figure
Prompt Photon and Inclusive Production at RHIC and LHC
We present results for prompt photon and inclusive production in p-p
and A-A collisions at RHIC and LHC energies. We include the full
next-to-leading order radiative corrections and nuclear effects, such as
nuclear shadowing and parton energy loss. We find the next-to-leading order
corrections to be large and dependent. We show how measurements of
production at RHIC and LHC, at large , can provide valuable
information about the nature of parton energy loss.
We calculate the ratio of prompt photons to neutral pions and show that at
RHIC energies this ratio increases with approaching one at
GeV, due to the large suppression of production. We show that at the
LHC, this ratio has steep dependence and approaches 10% effect at GeV.Comment: Talk presented by I. Sarcevic, to appear in the Proceedings of Quark
Matter 2002; 4 pages including 4 color figure
Multiplicity Fluctuations in Au+Au Collisions at RHIC
The preliminary data of the PHENIX collaboration for the scaled variances of
charged hadron multiplicity fluctuations in Au+Au at GeV are
analyzed within the model of independent sources. We use the HSD transport
model to calculate the participant number fluctuations and the number of
charged hadrons per nucleon participant in different centrality bins. This
combined picture leads to a good agreement with the PHENIX data and suggests
that the measured multiplicity fluctuations result dominantly from participant
number fluctuations. The role of centrality selection and acceptance is
discussed separately.Comment: 7 pages, 3 figures, submitted to Phys. Rev. C (Rapid Communication
Particle number fluctuations in nuclear collisions within excluded volume hadron gas model
The multiplicity fluctuations are studied in the van der Waals excluded
volume hadron-resonance gas model. The calculations are done in the grand
canonical ensemble within the Boltzmann statistics approximation. The scaled
variances for positive, negative and all charged hadrons are calculated along
the chemical freeze-out line of nucleus-nucleus collisions at different
collision energies. The multiplicity fluctuations are found to be suppressed in
the van der Waals gas. The numerical calculations are presented for two values
of hard-core hadron radius, fm and 0.5 fm, as well as for the upper
limit of the excluded volume suppression effects.Comment: 19 pages, 4 figure
Condensation for a fixed number of independent random variables
A family of m independent identically distributed random variables indexed by
a chemical potential \phi\in[0,\gamma] represents piles of particles. As \phi
increases to \gamma, the mean number of particles per site converges to a
maximal density \rho_c<\infty. The distribution of particles conditioned on the
total number of particles equal to n does not depend on \phi (canonical
ensemble). For fixed m, as n goes to infinity the canonical ensemble measure
behave as follows: removing the site with the maximal number of particles, the
distribution of particles in the remaining sites converges to the grand
canonical measure with density \rho_c; the remaining particles concentrate
(condensate) on a single site.Comment: 6 page
Multiplicity Fluctuations in Nucleus-Nucleus Collisions: Dependence on Energy and Atomic Number
Event-by-event multiplicity fluctuations in central C+C, S+S, In+In, and
Pb+Pb as well as p+p collisions at bombarding energies from 10 to 160 AGeV are
studied within the HSD and UrQMD microscopic transport approaches. Our
investigation is directly related to the future experimental program of the
NA61 Collaboration at the SPS for a search of the QCD critical point. The
dependence on energy and atomic mass number of the scaled variances for
negative, positive, and all charged hadrons is presented and compared to the
results of the model of independent sources. Furthermore, the nucleus-nucleus
results from the transport calculations are compared to inelastic proton-proton
collisions for reference. We find a dominant role of the participant number
fluctuations in nucleus-nucleus reactions at finite impact parameter . In
order to reduce the influence of the participant numbers fluctuations on the
charged particle multiplicity fluctuations only the most central events have to
be selected. Accordingly, the samples of the 1% most central nucleus-nucleus
collisions with the largest numbers of the projectile participants are studied.
The results are compared with those for collisions at zero impact parameter. A
strong influence of the centrality selection criteria on the multiplicity
fluctuations is pointed out. Our findings are essential for an optimal choice
of colliding nuclei and bombarding energies for the experimental search of the
QCD critical point.Comment: 26 pages, 12 figures, extended version, to be published in Phys. Rev.
Dissipation in equations of motion of scalar fields
The methods of non-equilibrium quantum field theory are used to investigate
the possibility of representing dissipation in the equation of motion for the
expectation value of a scalar field by a friction term, such as is commonly
included in phenomenological inflaton equations of motion. A sequence of
approximations is exhibited which reduces the non-equilibrium theory to a set
of local evolution equations. However, the adiabatic solution to these
evolution equations which is needed to obtain a local equation of motion for
the expectation value is not well defined; nor, therefore, is the friction
coefficient. Thus, a non-equilibrium treatment is essential, even for a system
that remains close to thermal equilibrium, and the formalism developed here
provides one means of achieving this numerically.Comment: 17 pages, 5 figure
- …