ABSTRACT
The energy loss of a relativistic charge undergoing multiple scatterings while traversing an infinite, polarizable and absorptive plasma is investigated. Polarization and absorption mechanisms in the medium are phenomenologically modeled by a complex index of refraction. Apart from the known Ter-Mikaelian effect related to the dielectric polarization of matter, we find an additional, substantial reduction of the energy loss due to the damping of radiation. The observed effect is more prominent for larger damping and/or larger energy of the charge. A conceivable analog of this phenomenon in QCD could influence the study of jet quenching phenomena in ultrarelativistic heavy-ion collisions at RHIC and LHC.
ABSTRACT
The recently discovered coexistence of multifragmentation and residue production for the same total transverse energy of light charged particles, which has been dubbed bimodality like it has been introduced in the framework of equilibrium thermodynamics, can be well reproduced in numerical simulations of heavy ion reactions. A detailed analysis shows that fluctuations (introduced by elementary nucleon-nucleon collisions) determine which of the exit states is realized. Thus, we can identify bifurcation in heavy ion reactions as a critical phenomenon. Also the scaling of the coexistence region with beam energy is well reproduced in these results from the quantum molecular dynamics simulation program.
ABSTRACT
The Nambu-Jona-Lasinio Lagrangian offers an explication of the seemingly contradictory observations that (a) the energy loss in the entrance channel of heavy ion reactions is not sufficient to thermalize the system and that (b) the observed hadron cross sections are in almost perfect agreement with hydrodynamical calculations. According to this scenario, a critical opacity develops close to the chiral phase transition which equilibrates and hadronizes the expanding system very effectively. It creates as well radial flow and, if the system is not isotropic, finite upsilon2 values.
ABSTRACT
A novel mechanism of H0 and strangelet production in hadronic interactions within the Gribov-Regge approach is presented. In this approach the H0 is produced by the same mechanism as usual hadrons, namely, by disintegration of the remnant formed by the exchange of pomerons between the two protons. Rapidity and transverse momentum spectra of the observed hadrons are well described in this approach. In contrast to traditional distillation approaches, here the production of multiple (strange) quark bags does not require large baryon densities or a quark gluon plasma. We calculate the rapidity and transverse momentum distributions as well as the 4pi multiplicity of the H0 for sqrt[s]=17 GeV (Super Proton Synchrotron) and 200 GeV (Relativistic Heavy Ion Collider). In both cases the H0, if it exists, should be observable by the present experiments.
ABSTRACT
In heavy ion reactions at energies around (1-2)A GeV the measured K- yields appear rather high as compared to pp collisions as shown by the KaoS Collaboration. Employing quantum molecular dy-namics simulations, we show that this is caused by the fact that the dominant production channel is not BB-->BBK+K- but the mesonic Lambda(Sigma)pi-->K-B reaction. Because the Lambda (Sigma) stem from the reaction BB-->Lambda(Sigma)K+B, the K+ and the K- yield are strongly correlated, i.e., the K(-)/K(+) ratio occurs to be nearly independent of the impact parameter as found experimentally. The final K- yield is strongly influenced by the K+N [due to their production via the Lambda(Sigma)] but very little by the K-N potential.
ABSTRACT
The Omega/Omega ratio originating from string decays is predicted to be larger than unity in proton-proton interactions at SPS energies ( E(lab) = 160 GeV). The antiomega dominance increases with decreasing beam energy. This surprising behavior is caused by the combinatorics of quark-antiquark production in small and low-mass strings. Since this behavior is not found in a statistical description of hadron production in proton-proton collisions, it may serve as a key observable to probe the hadronization mechanism in such collisions.
