arXiv subjects
Publications and source records attributed to J. I. Kapusta.
No conventional picture of nucleus-nucleus collisions has yet been able to explain the abundance of Omega and anti-Omega hyperons in central collisions between Pb nuclei at 158 A GeV at the CERN SPS. We argue that this is evidence that they are produced as topological defects arising from the formation of disoriented chiral condensates (DCC) with an average domain size of about 2 fm.
The mass shift, width broadening, and spectral density for the $ρ$ and $ω$ mesons in a heat bath of nucleons and pions are calculated using a general formula which relates the self-energy to the real and imaginary parts of the forward scattering amplitude. We use experimental data to saturate the scattering amplitude at low energies with resonances and include a background Pomeron term, while at high energies a Regge parameterization is used. The real part obtained directly is compared with the result of a dispersion integral over the imaginary part. The peaks of the spectral densities are little shifted from their vacuum positions, but the widths are considerably increased due to collisional broadening. Where possible we compare with the UrQMD model and find quite good agreement. At normal nuclear matter density and a temperature of 150 MeV the spectral density of the $ρ$ meson has a width of 345 MeV, while that for the $ω$ is in the range 90--150 MeV.
We compute bremsstrahlung arising from the acceleration of individual charged baryons and mesons during the time evolution of high-energy Au+Au collisions at the Relativistic Heavy Ion Collider using a microscopic transport model. We elucidate the connection between bremsstrahlung and charge stopping by colliding artificial pure proton on pure neutron nuclei. From the intensity of low energy bremsstrahlung, the time scale and the degree of stopping could be accurately extracted without measuring any hadronic observables.
We construct a black hole whose interior is the false vacuum and whose exterior is the true vacuum of a classical field theory. From the outside the metric is the usual Schwarzschild one, but from the inside the space is de Sitter with a cosmological constant determined by the energy of the false vacuum. The parameters of the field potential may allow for the false vacuum to exist for more than the present age of the universe. A potentially relevant effective field theory within the context of QCD results in a Schwarzschild radius of about 200 km.
We calculate the order α_s finite temperature correction to dilepton production in quark-gluon plasma arising from the two-loop photon self-energy diagrams for high invariant mass M >> T.
We calculate the change in the effective mass and width of a Z boson in the environment of a quark-gluon plasma under the conditions expected in Pb-Pb collisions at the LHC. The change in width is predicted to be only about 1 MeV at a temperature of 1 GeV, compared to the natural width of 2490$\pm$7 MeV. The mass shift is even smaller. Hence no observable effects are to be expected.
We examine the bremsstrahlung photons emitted in the central collisions of two gold nuclei at the Relativistic Heavy Ion Collider. While the measurements of the final hadrons can reveal only the amount of stopping, they tell us very little about the space-time evolution of the bulk matter in the collisions. By using two extreme collision scenarios, we argue that the low and medium energy bremsstrahlung photons can, not only reveal the amount of stopping, but also the finer details of the space-time evolution of the charges.
Our recent work on modifications of rho-mesons formed at the last stage of evolution of hadronic matter produced in heavy ion collisions is summarized. It is found that while the mass shift is on the order of a few tens of MeV, the width and spectral density become so broad that rho may lose its identity as a well defined resonance.
The bremsstrahlung produced when heavy nuclei collide is estimated for central collisions at the Relativistic Heavy Ion Collider. Bremsstrahlung photons with energies below 100 to 200 MeV are sufficient to discern the gross features of the space-time evolution of electric charge, if they can be separated from other sources of photons experimentally. This is illustrated explicitly by considering two very different models, one Bjorken-like, the other Landau-like, both of which are constructed to give the same final charge rapidity distribution.
The mass shift and width broadening of $ρ$-mesons produced in heavy ion collisions is estimated. It is found that the mass increases by some tens of MeV but the width becomes large, increasing by 200 MeV at beam energies of a few GeV$\cdot$A and by twice that amount at beam energies of about a hundred GeV$\cdot$A.
The rho-meson mass shift, width broadening, and spectral density at finite temperature and nucleon density are estimated using a general formula which relates the self-energy to the real and imaginary parts of the forward scattering amplitude on the constituents of the medium. We saturate the scattering amplitude at low energies with resonances, while at high energies a Regge approach is taken in combination with vector meson dominance; experimental data is used wherever possible. The main result is that the rho-meson becomes increasingly broad with increasing nucleon density. The spectral density is suppressed in the resonance region 600 < M < 900 MeV and enhanced in the subresonance region M < 600 MeV.
The mass shift and width broadening of rho-mesons produced in heavy ion collisions is estimated using general formulae which relate the in-medium mass shift of a particle to the real part of the forward scattering amplitude of this particle on constituents of the medium and the width broadening to the corresponding cross section. It is found that the mass increases by some tens of MeV but, more importantly, the width becomes large, increasing by several hundred MeV at beam energies of a few GeV per nucleon and by twice that amount at beam energies of about a hundred GeV per nucleon.
The mass shift $Δm_ρ$ and width broadening $ΔΓ_ρ$ of $ρ$ mesons produced in heavy ion collisions is estimated using a general formula which relates the in-medium mass shift of a particle to the real part of the forward scattering amplitude ${\rm Re} f(E)$ of this particle on constituents of the medium and $ΔΓ$ to the corresponding cross section. It is found that in high energy ($E/A \ga 100~$GeV) heavy ion collisions the $ρ$ width broadening is large and $ρ$ (or $ω$) peak could hardly be observed in $e^+e^-(μ^+μ^-)$ effective mass distributions. In low energy collisions ($E/A \sim$ a few GeV) a broad (a few hundred MeV) enhancement is expected at the position of the $ρ$ peak.
Coarse-grained Langevin-type effective field equations are derived for classical systems of particles. These equations include the effects of thermal fluctuation and dissipation which may arise from coupling to an external bath, as in the Brownian motion of a single particle, or which may arise from statistical fluctuations in small parts of an isolated many-particle system, as in sound waves. These equations may provide some guidance for the analysis of mesoscopic or microscopic molecular systems, or for systems of hundreds to thousands of subatomic particles produced in high energy nuclear collisions.
The energy densities achieved during central collisions of large nuclei at Brookhaven's AGS may be high enough to allow the formation of quark--gluon plasma. Calculations based on relativistic nucleation theory suggest that rare events, perhaps one in every 10$^2$ or 10$^3$, undergo the phase transition. Experimental ramifications may include an enhancement in the ratio of pions to baryons, a reduction in the ratio of deuterons to protons, and a larger source size as seen by hadron interferometry.
This comment is hereby withdrawn, because the paper by D. Seibert, KSUCNR-005-94 and nucl-th/9403005 was withdrawn and it was acknowleged that the parton cascade model does approach chemical equilibrium correctly. Therefore our reply to Seibert's paper is now obsolete.
We use an effective low energy field theory to describe the coupling between glueballs and mesons as an analog of the quenched approximation in lattice QCD. This allows us to study the temperature dependence of mesonic screening masses at temperatures below the deconfinement phase transition.
We consider sum rules of the Weinberg type at zero and nonzero temperatures. On the basis of the operator product expansion at zero temperature we obtain a new sum rule which involves the average of a four-quark operator on one side and experimentally measured spectral densities on the other. We further generalize the sum rules to finite temperature. These involve transverse and longitudinal spectral densities at each value of the momentum. Various scenarios for the relation between chiral symmetry restoration and these finite temperature sum rules are discussed.