14304615
Baryon, charged hadron, Drell-Yan and J/{psi} production in high energy proton-nucleus collisions
We show that the distributions of outgoing protons and charged hadrons in high energy proton-nucleus collisions are described rather well by a linear extrapolation from proton-proton collisions. The only adjustable parameter required is the shift in rapidity of a produced charged meson when it encounters a target nucleon. Its fitted value is 0.16. Next, we apply this linear extrapolation to precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets which exhibit a deviation from linear scaling in the atomic number {ital A}. We show that this deviation can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quantum coherence. We infer an average proper coherence time of 0.4{plus_minus}0.1hfm/c, corresponding to a coherence path length of 8{plus_minus}2hfm in the rest frame of the nucleus. Finally, we apply the linear extrapolation to measured J/{psi} production cross sections for 200 and 450 GeV/c protons incident on a variety of nuclear targets. Our analysis takes into account energy loss of the beam proton, the time delay of particle production due to quantum coherence, and absorption of the J/{psi}more » on nucleons. The best representation is obtained for a coherence time of 0.5 fm/c, which is consistent with Drell-Yan production, and an absorption cross section of 3.6 mb, which is consistent with the value deduced from photoproduction of the J/{psi} on nuclear targets. {copyright} {ital 1999 American Institute of Physics.}« less
14039368
High temperature matter and gamma-ray spectra from microscopic black holes
The relativistic viscous fluid equations describing the outflow of high temperature matter created via Hawking radiation from microscopic black holes are solved numerically for a realistic equation of state. We focus on black holes with initial temperatures greater than 100 GeV and lifetimes less than 6 days. The spectra of direct photons and photons from $\pi^0$ decay are calculated for energies greater than 1 GeV. We calculate the diffuse gamma ray spectrum from black holes distributed in our galactic halo. However, the most promising route for their observation is to search for point sources emitting gamma rays of ever-increasing energy.
14800892
Hydrogenlike 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.
122503286
EVIDENCE FOR A SOFT NUCLEAR MATTER EQUATION OF STATE
The entropy of the fireball formed in central collisions of heavy nuclei at center-of-mass kinetic energies of a few hundred MeV per nucleon is estimated from the ratio of deuterons to protons at large transverse momentum. The observed paucity of deuterons suggests that strong attractive forces are present in hot, dense nuclear matter, or that degrees of freedom beyond the nucleon and pion may already be realized at an excitation energy of 100 MeV per baryon.
115314153
Status of the theory of QCD plasma
There is mounting evidence, based on many theoretical approaches, that color is deconfined and chiral symmetry is restored at temperatures greater than about 200 MeV. Reasonable estimates of the energy density to be expected in high energy heavy ion collisions suggest that QCD plasma may be formed in the laboratory. Proposed experimental signals may allow us to infer such quantities as the temperature, the quark dispersion relation, the space-time evolution and, perhaps, even the order of the phase transition. 52 references.
121913464
Transverse Momentum Spectrum of Mesons Produced in High-energy Nucleus-nucleus Collisions
Abstract The momentum of all charged mesons produced in 19 high energy, high multiplicity nucleus-nucleus collisions of cosmic rays in emulsion have been measured. The transverse momentum distribution differs qualitatively from proton-proton collisions at comparable energies. One possible interpretation is in terms of a transverse explosion with effective temperature T =78 MeV and transverse flow velocity υ =0.61 c .
15653990
Missing Molecular Hydrogen and the Physical Conditions of GRB Host Galaxies
We examine the abundance of molecular hydrogen (H2) in the spectra of gamma ray burst afterglows (GRBs). In nearby galaxies, H2 traces the cold neutral medium (CNM) and dense molecular star-forming interstellar gas. Although H2 is detected in at least half of all sight lines toward hot stars in the Magellanic Clouds and in ≈25% of damped Lyα systems toward quasars, it is not detected in any of the five GRB environments with a similar range of neutral hydrogen column density and metallicity. We detect no vibrationally excited H2 that would imply that the GRB itself has photodissociated its parent molecular cloud, so such models are ruled out unless the parent cloud was 4 pc in radius and was fully dissociated prior to the spectroscopic observations, or the star escaped its parent cloud during its main-sequence lifetime. The low molecular fractions for the GRBs are mysterious in light of their large column densities of neutral H and expectations based on local analogs, i.e., 30 Doradus in the LMC. This surprising lack of H2 in GRB damped Lyα absorbers indicates that the destruction processes that suppress molecule formation in the LMC and SMC are more effective in the GRB hosts, most probably due to a combination of low metallicity and an FUV radiation field 10-100 times the Galactic mean field. These inferred conditions place strong constraints on the star-forming regions in these early galaxies.
119115901
Pseudo-Dirac Neutrinos in the New Standard Model
The addition of gauge-singlet fermions to the standard model Lagrangian renders the neutrinos massive and allows one to explain all that is experimentally known about neutrino masses and lepton mixing by varying the values of the Majorana mass parameters M for the gauge singlets and the neutrino Yukawa couplings {lambda}. Here we explore the region of parameter space where M values are much smaller than the neutrino Dirac masses {lambda}v. In this region, neutrinos are pseudo-Dirac fermions. We find that current solar data constrain M values to be less than at least 10{sup -9} eV, and discuss the sensitivity of future experiments to tiny gauge-singlet fermion masses. We also discuss a useful basis for analyzing pseudo-Dirac neutrino mixing effects. In particular, we identify a simple relationship between elements of M and the induced enlarged mixing matrix and new mass-squared differences. These allow one to directly relate bounds on the new mass-squared differences to bounds on the singlet fermion Majorana masses.