Nucleus-Nucleus Bremsstrahlung from Ultrarelativistic Collisions

The bremsstrahlung produced when heavy nuclei collide is estimated for central collisions at the Relativistic Heavy Ion Collider. Soft photons can be used to infer the rapidity distribution of the outgoing charge. An experimental design is outlined.Comment: 12 pages, 7 figures, uses revte

Jet energy loss and high pTp_T photon production in hot quark-gluon plasma

Jet-quenching and photon production at high transverse momentum are studied at RHIC energies, together with the correlation between jets and photons. The energy loss of hard partons traversing the hot QGP is evaluated in the AMY formalism, consistently taking into account both induced gluon emission and elastic collisions. The production of high $p_T$ photons in Au+Au collisions is calculated, incorporating a complete set of photon-production channels. Putting all these ingredients together with a (3+1)-dimensional ideal relativistic hydrodynamical description of the thermal medium, we achieve a good description of the current experimental data. Our results illustrate that the interaction between hard jets and the soft medium is important for a complete understanding of jet quenching, photon production, and photon-hadron correlations in relativistic nuclear collisions.Comment: 4 pages, 4 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

Zero range model of traffic flow

A multi--cluster model of traffic flow is studied, in which the motion of cars is described by a stochastic master equation. Assuming that the escape rate from a cluster depends only on the cluster size, the dynamics of the model is directly mapped to the mathematically well-studied zero-range process. Knowledge of the asymptotic behaviour of the transition rates for large clusters allows us to apply an established criterion for phase separation in one-dimensional driven systems. The distribution over cluster sizes in our zero-range model is given by a one--step master equation in one dimension. It provides an approximate mean--field dynamics, which, however, leads to the exact stationary state. Based on this equation, we have calculated the critical density at which phase separation takes place. We have shown that within a certain range of densities above the critical value a metastable homogeneous state exists before coarsening sets in. Within this approach we have estimated the critical cluster size and the mean nucleation time for a condensate in a large system. The metastablity in the zero-range process is reflected in a metastable branch of the fundamental flux--density diagram of traffic flow. Our work thus provides a possible analytical description of traffic jam formation as well as important insight into condensation in the zero-range process.Comment: 10 pages, 13 figures, small changes are made according to finally accepted version for publication in Phys. Rev.

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

Quark Number Fluctuations in a Chiral Model at Finite Baryon Chemical Potential

We discuss the net quark and isovector fluctuations as well as off-diagonal quark flavor susceptibilities along the chiral phase transition line in the Nambu--Jona-Lasinio (NJL) model. The model is formulated at non-zero quark and isospin chemical potentials with non-vanishing vector couplings in the iso-scalar and iso-vector channels. We study the influence of the quark chemical potential on the quark flavour susceptibilities in detail and the dependence of the results on model parameters as well as on the quark mass. The NJL model findings are compared with recent lattice results obtained in two--flavor QCD at finite chemical potential. On a qualitative level, the NJL model provides a consistent description of the dependence of quark number fluctuations on temperature and baryon chemical potential. The phase diagram and the position of the tricritical point in the NJL model are also discussed for different parameter sets.Comment: 33 pages, 11 figures; final version accepted for publication in Phys. Rev.

Nonequilibrium perturbation theory for spin-1/2 fields

A partial resummation of perturbation theory is described for field theories containing spin-1/2 particles in states that may be far from thermal equilibrium. This allows the nonequilibrium state to be characterized in terms of quasiparticles that approximate its true elementary excitations. In particular, the quasiparticles have dispersion relations that differ from those of free particles, finite thermal widths and occupation numbers which, in contrast to those of standard perturbation theory evolve with the changing nonequilibrium environment. A description of this kind is essential for estimating the evolution of the system over extended periods of time. In contrast to the corresponding description of scalar particles, the structure of nonequilibrium fermion propagators exhibits features which have no counterpart in the equilibrium theory.Comment: 16 pages; no figures; submitted to Phys. Rev.

Color conductivity and ladder summation in hot QCD

The color conductivity is computed at leading logarithmic order using a Kubo formula. We show how to sum an infinite series of planar ladder diagrams, assuming some approximations based on the dominance of soft scattering processes between hard particles in the plasma. The result agrees with the one obtained previously from a kinetical approach.Comment: 15 pages, 4 figures. Explanations enlarged, two figures and some refs added, typos corrected. Final version to be published in Phys.Rev.

Neutron and muon-induced background studies for the AMoRE double-beta decay experiment

AMoRE (Advanced Mo-based Rare process Experiment) is an experiment to search a neutrinoless double-beta decay of $^{100}$Mo in molybdate crystals. The neutron and muon-induced backgrounds are crucial to obtain the zero-background level (<$10^{-5}$ counts/(keV$\cdot$kg$\cdot$yr)) for the AMoRE-II experiment, which is the second phase of the AMoRE project, planned to run at YEMI underground laboratory. To evaluate the effects of neutron and muon-induced backgrounds, we performed Geant4 Monte Carlo simulations and studied a shielding strategy for the AMORE-II experiment. Neutron-induced backgrounds were also included in the study. In this paper, we estimated the background level in the presence of possible shielding structures, which meet the background requirement for the AMoRE-II experiment

Anomalous Multiplicity Fluctuations from Phase Transitions in Heavy Ion Collisions

Event-by-event fluctuations and correlations between particles produced in relativistic nuclear collisions are studied. The fluctuations in positive, negative, total and net charge are closely related through correlations. In the event of a phase transitions to a quark-gluon plasma, fluctuations in total and net charge can be enhanced and reduced respectively which, however, is very sensitive to the acceptance and centrality. If the colliding system experiences strong density fluctuations due, e.g., to droplet formation in a first-order phase transition, all fluctuations can be enhanced substantially. The importance of fluctuations and correlations is exemplified by event-by-event measurement of the multiplicities of $J/\Psi$'s and charged particles since these observables should anti-correlate in the presence of co-mover or anomalous absorption.Comment: revised version to appear in Phys. Rev. C, 5 page