Exclusive and inclusive muon pair production in collisions of relativistic nuclei

The exclusive production of one $\mu^+\mu^-$ pair in collisions of two ultra-relativistic nuclei is considered. We present a simple method for the calculation of the Born cross section for this process based on an improved equivalent photon approximation. We find that the Coulomb corrections to this cross section (corresponding to multi-photon exchange of the produced $\mu^{\pm}$ with the nuclei) are small while the unitarity corrections (corresponding to the exchange of light-by-light blocks between nuclei) are large. This is in sharp contrast to the exclusive $e^+e^-$ pair production where the Coulomb corrections to the Born cross section are large while the unitarity corrections are small. We calculate also the cross section for the production of one $\mu^+\mu^-$ pair and several $e^+e^-$ pairs in the leading logarithmic approximation. Using this cross section we find that the inclusive production of $\mu^+\mu^-$ pair coincides in this approximation with its Born value.Comment: 16 pages, 4 figure

Nuclear Breakup of Borromean Nuclei

We study the eikonal model for the nuclear-induced breakup of Borromean nuclei, using Li11 and He6 as examples. The full eikonal model is difficult to realize because of six-dimensional integrals, but a number of simplifying approximations are found to be accurate. The integrated diffractive and one-nucleon stripping cross sections are rather insensitive to the neutron-neutron correlation, but the two-nucleon stripping does show some dependence on the correlation. The distribution of excitation energy in the neutron-core final state in one-neutron stripping reactions is quite sensitive to the shell structure of the halo wave function. Experimental data favor models with comparable amounts of s- and p-wave in the Li11 halo.Comment: 34 pages REVTeX, 14 postscript figures. Small changes in comparison with experimen

Production of Low Mass Electron Pairs Due to the Photon-Photon Mechanism in Central Collisions

We calculate the probability for dilepton production in central relativistic heavy ion collisions due to the gamma-gamma mechanism. This is a potential background to more interesting mechanisms. We find that this mechanism is negligible in the CERES experiments. Generally, the contribution due to this mechanism is small in the central region, while it can be large for small invariant masses and forward or backward rapidities. A simple formula based on the equivalent photon approximation and applications to a possible scenario at RHIC are also given.Comment: 10 pages REVTeX, 5 Figures, for related work see http://quasar.physik.unibas.ch/~hencken

Bremsstrahlung Pair Production In Relativistic Heavy Ion Collision

We calculate production of electron- and muon-pairs by the bremsstrahlung process in hadron collisions and compare it with the dominant two-photon process. Results for the total cross section are given for proton-proton and heavy-ion collisions at energies of the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).Comment: 6 pages, Latex, 9 figures using epsf-style. Accepted for publication in Z. Phys.

Multiple electromagnetic electron positron pair production in relativistic heavy ion collisions

We calculate the cross sections for the production of one and more electron-positron pairs due to the strong electromagnetic fields in relativistic heavy ion collisions. Using the generating functional of fermions in an external field we derive the N-pair amplitude. Neglecting the antisymmetrisation in the final state we find that the total probability to produce N pairs is a Poisson distribution. We calculate total cross sections for the production of one pair in lowest order and also include higher-order corrections from the Poisson distribution up to third order. Furthermore we calculate cross sections for the production of up to five pairs including corrections from the Poisson distribution.Comment: 13 pages REVTeX, 4 Postscript figures, This and related papers may also be obtained from http://www.phys.washington.edu/~hencken

Photon-Photon and Photon-Hadron Physics at Relativistic Heavy Ion Colliders

Due to the coherence of all the protons in a nucleus, there are very strong electromagnetic fields of short duration in relativistic heavy ion collisions. They give rise to quasireal photon-photon and photon-nucleus collisions with a large flux. RHIC will begin its experimental program this year and such types of collisions will be studied experimentally at the STAR detector. RHIC will have the highest flux of (quasireal) photons up to now in the GeV region. At the LHC the invariant mass range available in gamma-gamma-interactions will be of the order of 100 GeV, i.e., in the range currently available at LEP2, but with a higher gamma-gamma-luminosity. Therefore one has there also the potential to study new physics. (Quasireal) photon-hadron (i.e., photon-nucleus) interactions can be studied as well, similar to HERA, at higher invariant masses. Vector mesons can be produced coherently through photon-Pomeron and photon-meson interactions in exclusive reactions such as A+A -> A+A+V, where A is the heavy ion and V=rho,omega,phi or J/Psi.Comment: 6 pages, to be published in the proceedings of the Photon'99 conferenc

Electron-positron pair production in the external electromagnetic field of colliding relativistic heavy ions

The results concerning the $e^+e^-$ production in peripheral highly relativistic heavy-ion collisions presented in a recent paper by Baltz {\em{et al.}} are rederived in a very straightforward manner. It is shown that the solution of the Dirac equation directly leads to the multiplicity, i.e. to the total number of electron-positron pairs produced by the electromagnetic field of the ions, whereas the calculation of the single pair production probability is much more involved. A critical observation concerns the unsolved problem of seemingly absent Coulomb corrections (Bethe-Maximon corrections) in pair production cross sections. It is shown that neither the inclusion of the vacuum-vacuum amplitude nor the correct interpretation of the solution of the Dirac equation concerning the pair multiplicity is able the explain (from a fundamental point of view) the absence of Coulomb corrections. Therefore the contradiction has to be accounted to the treatment of the high energy limit.Comment: 6 pages, 4 Postscript figures, uses svjour.cls/svepj.cl

Mechanisms for Direct Breakup Reactions

We review some simple mechanisms of breakup in nuclear reactions. We mention the spectator breakup, which is described in the post-form DWBA. The relation to other formulations is also indicated. An especially important mechanism is Coulomb dissociation. It is a distinct advantage that the perturbation due to the electric field of the nucleus is exactly known. Therefore firm conclusions can be drawn from such measurements. Some new applications of Coulomb dissociation for nuclear astrophysics are discussed.Comment: 17 pages, 5 figures, to appear in the proceedings of the RCNP-TMU Symposium on Spins in Nuclear and Hadronic Reactions, October 16-18 199