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 Dirac delta function of (z - t) times the simple two dimensional potential solution in the transverse direction. This form makes manifest the source of the energy independence of the interaction.Comment: 5 pages, latex, revtex source, no figure

Some exact analytical results and a semi-empirical 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 semi-empirical 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.Comment: 14 pages, latex, revtex source, no figure

Higher Order QED Calculation of Ultrarelativistic Heavy Ion Production of mu+ mu- Pairs

A higher order QED calculation of the ultraperipheral heavy ion cross section for mu+ mu- pair production at RHIC and LHC is carried out. The so-called "Coulomb corrections" lead to an even greater percentage decrease of mu+ mu- production from perturbation theory than the corresponding decrease for e+ e- pair production. Unlike the e+ e- case, the finite charge distribution of the ions (form factor) and the necessary subtraction of impact parameters with matter overlap are significant effects in calculation an observable ultraperipheral mu+ mu- total cross section.Comment: 7 pages, 3 figures. Version expanded with explanatory text and two appendices on form factor treatmen

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.Comment: 22 pages, latex, revtex source, one postscript figur

Evidence for higher order QED in e+ e- pair production at RHIC

A new lowest order QED calculation for RHIC e+ e- pair production has been carried out with a phenomenological treatment of the Coulomb dissociation of the heavy ion nuclei observed in the STAR ZDC triggers. The lowest order QED result for the experimental acceptance is nearly two standard deviations larger than the STAR data. A corresponding higher order QED calculation is consistent with the data.Comment: 4 pages, 4 figures, latex, revte

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

The heavy ion probability for continuum e+ e- 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+ e- pair production is reduced from the perturbation theory result throughout the impact parameter range.Comment: 20 pages, latex, revtex, 6 eps figures. Revised Phys. Rev. C version with minor additions, one figure added, and added reference

A light-fronts approach to electron-positron pair production in ultrarelativistic heavy-ion collisions

We perform a gauge-transformation on the time-dependent Dirac equation describing the evolution of an electron in a heavy-ion collision to remove the explicit dependence on the long-range part of the interaction. We solve, in an ultra-relativistic limit, the gauged-transformed Dirac equation using light-front variables and a light-fronts representation, obtaining non-perturbative results for the free pair-creation amplitudes in the collider frame. Our result reproduces the result of second-order perturbation theory in the small charge limit while non-perturbative effects arise for realistic charges of the ions.Comment: 39 pages, Revtex, 7 figures, submitted to PR

Process 3 -> 3 and crossing symmetry violation

Using the Sudakov technique we sum the perturbation series for the process $3\to 3$ and obtain the compact analytical expression for the amplitude of this process, which takes into account all possible Coulomb interactions between colliding particles. Compare it with the amplitude of the lepton pair production in heavy ion collision i.e. in the process $2\to 4$, we show that crossing symmetry between this processes holds only if one neglects the interaction of produced pair with ions (i.e. in the approximation $Z_{1,2}\alpha \ll 1$).Comment: LaTeX2e, 10 pages, 5 eps figure

Exact Z2Z^2 scaling of pair production in the high-energy limit of heavy-ion collisions

The two-center Dirac equation for an electron in the external electromagnetic field of two colliding heavy ions in the limit in which the ions are moving at the speed of light is exactly solved and nonperturbative amplitudes for free electron-positron pair production are obtained. We find the condition for the applicability of this solution for large but finite collision energy, and use it to explain recent experimental results. The observed scaling of positron yields as the square of the projectile and target charges is a result of an exact cancellation of a nonperturbative charge dependence and holds as well for large coupling. Other observables would be sensitive to nonperturbative phases.Comment: 4 pages, Revtex, no figures, submitted to PR