35 research outputs found
Heavy Ion e+ e- Pairs to All Orders in Z alpha
The heavy ion cross section for continuum e+ e- pair production has been
calculated to all orders in Z alpha. Comparison is made with available CERN SPS
and RHIC STAR data. Computed cross sections are found to be reduced from
perturbation theory with increasing charge of the colliding heavy ions and for
all energy and momentum regions investigated. Au or Pb total cross sections are
reduced by 28% (SPS), 17% (RHIC),and 11% (LHC). For very high energy (E_e+,
E_e- > 3 GeV) forward pairs at LHC the reduction from perturbation theory is a
bit larger (17%). Use of zero degree calorimeter triggering (and thus small
impact parameter weighting) makes impact parameter representation of exact pair
production useful. Preliminary exact calculations in the zero impact parameter
limit show a much larger reduction from perturbation theory (about 40%) at both
RHIC and LHC.Comment: 4 pages, poster proceedings from Quark Matter 200
Higher order QED in high mass e+ e- pairs production at RHIC
Lowest order and higher order QED calculations have been carried out for the
RHIC high mass e+ e- pairs observed by PHENIX with single ZDC triggers. The
lowest order QED results for the experimental acceptance are about two standard
deviations larger than the PHENIX data. Corresponding higher order QED
calculations are within one standard deviation of the data.Comment: 2 page
Correlated forward-backward dissociation and neutron spectra as a luminosity monitor in heavy ion colliders
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.Comment: 16 pages, latex, revtex source, four postscript figure
Aspects of Coulomb Dissociation and Interference in Peripheral Nucleus-Nucleus Collisions
Coherent vector meson production in peripheral nucleus-nucleus collisions is
discussed. These interactions may occur for impact parameters much larger than
the sum of the nuclear radii. Since the vector meson production is always
localized to one of the nuclei, the system acts as a two-source interferometer
in the transverse plane. By tagging the outgoing nuclei for Coulomb
dissociation it is possible to obtain a measure of the impact parameter and
thus the source separation in the interferometer. This is of particular
interest since the life-time of the vector mesons are generally much shorter
than the impact parameters of the collisions.Comment: 10 pages, 4 figures, Presented at the Workshop on Electromagnetic
Probes of Fundamental Physics, Erice, Italy, 16-21 October, 200
Two-Photon Interactions with Nuclear Breakup in Relativistic Heavy Ion Collisions
Highly charged relativistic heavy ions have high cross-sections for
two-photon interactions. The photon flux is high enough that two-photon
interactions may be accompanied by additional photonuclear interactions. Except
for the shared impact parameter, these interactions are independent. Additional
interactions like mutual Coulomb excitation are of experimental interest, since
the neutrons from the nuclear dissociation provide a simple, relatively
unbiased trigger.
We calculate the cross sections, rapidity, mass and transverse momentum
( distributions for exclusive production of mesons and
lepton pairs, and for reactions accompanied by mutual Coulomb
dissociation. The cross-sections for interactions accompanied by
multiple neutron emission () and single neutron emission () are
about 1/10 and 1/100 of that for the unaccompanied interactions.
We discuss the accuracy with which these cross-sections may be calculated. The
typical of final states is several times smaller than for
comparable coherent photonuclear interactions, so may be an effective
tool for separating the two classes of interactions.Comment: 17 pages, 12 figure
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.Comment: 14 pages, including 4 figure
Pair Production from 10 GeV to 10 ZeV
At very high energies, pair production () exhibits many
interesting features. The momentum transfer from the target is very small, so
the reaction probes the macroscopic properties of the target, rather than
individual nuclei. Interference between interactions with different atoms
reduces the pair production cross section considerably below the Bethe-Heitler
values. At very high energies, photonuclear interactions may outnumber pair
production.
In contrast, in crystals, the interaction amplitudes may add coherently,
greatly increasing the cross sections. Pair production in matter-free magnetic
fields is also possible. The highest energy pair production occurs at high
energy particle colliders. This article will compare pair production in these
very different regimes.Comment: 37 pages with 9 figures. Invited Review for "Radiation Physics and
Chemistry" Version for publication, incorporating comments by the referee,
and by Gerhard Baur and Roman Le
The Solar Neutrino Puzzle: An Oscillation Solution with Maximal Neutrino Mixing
If, as suggested by the SuperKamiokande results, the mu neutrino and tau
neutrino are maximally and ``rapidly'' mixed, this alone determines the mapping
from current to mass eigenstates up to one rotation angle (theta) mixing the
electron neutrino ``more slowly'', with an equal combination of the mu neutrino
and tau neutrino. For sin 2 theta = 1, the resulting minimal number of free
parameters, yet maximal mixing, shows agreement between extant observations of
solar neutrinos and predictions by the standard solar model with minor
modifications.Comment: 10 pages, latex, revtex source, two postscript figure