Anthony J. Baltz

SOLAR NEUTRINO PUZZLE: AN OSCILLATION SOLUTION WITH MAXIMAL NEUTRINO MIXING

If, as suggested by the Super-Kamiokande results, {nu}{sub {mu}} and {nu}{sub {tau}} are maximally and {open_quotes}rapidly{close_quotes} ({Delta}m{sup 2}{approx}2.2{times}10{sup {minus}3} eV{sup 2} ) mixed, this alone determines the mapping from current to mass eigenstates up to one rotation angle {theta} mixing {nu}{sub e} {open_quotes}more slowly{close_quotes} with a particular, equal-weight combination of {nu}{sub {mu}} and {nu}{sub {tau}} . For sinthinsp2{theta}=1 , the resulting minimal number of free parameters, yet maximal mixing, shows agreement, with minor modifications, between extant observations of solar neutrinos and predictions by the standard solar model. {copyright} {ital 1998} {ital The American Physical Society}

Coherent vector-meson photoproduction with nuclear breakup in relativistic heavy-ion collisions.

Relativistic heavy ions are copious sources of virtual photons. The large photon flux gives rise to a substantial photonuclear interaction probability at impact parameters where no hadronic interactions can occur. Multiple photonuclear interactions in a single collision are possible. In this Letter, we use mutual Coulomb excitation of both nuclei as a tag for moderate-impact-parameter collisions. We calculate the cross section for coherent vector-meson production accompanied by mutual excitation and show that the median impact parameter is much smaller than for untagged production. The vector-meson rapidity and transverse-momentum distribution are very different from untagged exclusive vector-meson production.

Coulomb corrections to e+e− production in ultra-relativistic nuclear collisions

Abstract The purpose of this paper is to explain the discrepancies existing in the literature relative to e + e − pair production in peripheral heavy ion collisions at ultra-relativistic energies. A controversial issue is the possible cancellation of Coulomb corrections to the Born term in the pair production cross-section. Such a cancellation has been observed in a recent approach based on finding retarded solutions of the Dirac equation, but does not seem to hold in a perturbative approach. We show in this paper that the two approaches are in fact calculating different observables: the perturbative approach gives the exclusive cross-section of single pair production, while the other method gives the inclusive cross-section. We have also performed a thorough study of the electron propagator in the non-static background field of the two nuclei, the conclusion of which is that the retarded propagator is in the ultra-relativistic limit a much simpler object than the Feynman propagator, and can be calculated exactly.

Two center light cone calculation of pair production induced by ultrarelativistic heavy ions

An exact solution of the two center time-dependent Dirac equation for pair production induced by ultrarelativistic heavy ion collisions is presented. Cross sections to specific final states approach those of perturbation theory. Multiplicity rates are reduced from perturbation theory. {copyright} {ital 1998} {ital The American Physical Society}

Correlated forward-backward dissociation and neutron spectra as a luminosity monitor in heavy ion colliders

Abstract Detection in zero degree calorimeters of the correlated forward–backward Coulomb or nuclear dissociation of two colliding nuclei is presented as a practical luminosity monitor in heavy-ion colliders. Complementary predictions are given for total correlated Coulomb plus nuclear dissociation and for correlated forward–backward single neutrons from the giant dipole peak.

Coulomb potential from a particle in uniform ultrarelativistic motion

The Coulomb potential produced by an ultrarelativistic particle (such as a heavy ion) in uniform motion is shown in the appropriate gauge to factorize into a longitudinal {delta}({ital z}{minus}{ital t}) dependence times a simple two-dimensional potential solution in the transverse direction. This form makes manifest the source of the energy independence of the interaction.

Coulomb corrections in the calculation of ultrarelativistic heavy ion production of continuum e+e- pairs

Coulomb corrections to perturbation theory for producing electron-positron pairs in ultrarelativistic heavy ion collisions are considered in a part-analytical, part-numerical approach. Production probabilities are reduced from perturbation theory with increasing charge of the colliding heavy ions, as has been previously argued in the literature. It is shown here that the reduction from perturbation theory comes from the appropriate physical spatial cutoff of the electromagnetic potentials arising from the colliding ultrarelativistic heavy ions.

Impact parameter dependence of heavy ion e+ e- pair production to all orders in Z alpha

The heavy ion probability for continuum e{sup +}e{sup -} pair production has been calculated to all orders in Z{alpha} as a function of impact parameter. The formula resulting from an exact solution of the semiclassical Dirac equation in the ultrarelativistic limit is evaluated numerically. In a calculation of {gamma}=100 colliding Au ions, the probability of e{sup +}e{sup -} pair production is reduced from the perturbation theory result throughout the impact parameter range.

Some exact analytical results and a semiempirical formula for single electron ionization induced by ultrarelativistic heavy ions

The {delta} function gauge of the electromagnetic potential allows semiclassical formulas to be obtained for the probability of exciting a single electron out of the ground state in an ultrarelativistic heavy-ion reaction. Exact formulas have been obtained in the limits of zero impact parameter and large, perturbative, impact parameter. The perturbative impact parameter result can be exploited to obtain a semiempirical cross section formula of the form {sigma}=A ln{gamma}+B for single-electron ionization. A and B can be evaluated for any combination of target and projectile, and the resulting simple formula is good at all ultrarelativistic energies. The analytical form of A and B elucidates a result previously found in numerical calculations: scaled ionization cross sections decrease with increasing charge of the nucleus being ionized. The cross section values obtained from the present formula are in good agreement with recent CERN SPS data from a Pb beam on various nuclear targets.

Exact Dirac-equation calculation of ionization induced by ultrarelativistic heavy ions

The time-dependent Dirac equation can be solved exactly for ionization induced by ultrarelativistic heavy-ion collisions. Ionization calculations are carried out in such a framework for a number of representative ion-ion pairs. For each ion-ion pair, the computed cross section consists of two terms: a constant energy independent term and a term whose coefficient is ln {gamma}. Scaled values of both terms are found to decrease with increasing Z of the nucleus that is ionized. (c) 2000 The American Physical Society.