1,499 research outputs found
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
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 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
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
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
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
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