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A. J. Baltz

Publications and source records attributed to A. J. Baltz.

12 recordsLinked to original sources
arXiv2013

Measurement of the total cross section of uranium-uranium collisions at $\sqrt{s_{NN}}=192.8$ GeV

Heavy ion cross sections totaling several hundred barns have been calculated previously for the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These total cross sections are more than an order of magnitude larger than the geometric ion-ion cross sections primarily due to Bound-Free Pair Production (BFPP) and Electro-Magnetic Dissociation (EMD). Apart from a general interest in verifying the calculations experimentally, an accurate prediction of the losses created in the heavy ion collisions is of practical interest for the LHC, where some collision products are lost in cryogenically cooled magnets and have the potential to quench these magnets. In the 2012 RHIC run uranium ions collided with each other at $\sqrt{s_{NN}} = 192.8$ GeV with nearly all beam losses due to collisions. This allows for the measurement of the total cross section, which agrees with the calculated cross section within the experimental error.

nucl-ex↗
arXiv2009

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.

nucl-th↗
arXiv2007

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.

nucl-th↗
arXiv2007

The Physics of Ultraperipheral Collisions at the LHC

We discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon-nucleon (nucleus) interactions. The current LHC detector configurations can explore small $x$ hard phenomena with nuclei and nucleons at photon-nucleon center-of-mass energies above 1 TeV, extending the $x$ range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic $J/ψ$ and $Υ$ production as well as in high $t$ $ρ^0$ production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements.

nucl-ex↗
arXiv2001

Probing an extended region of Delta m^2 with rapidly oscillating 7Be solar neutrinos

If 7Be solar neutrinos can be observed in real time experiments, then an extended region of Delta m^2 can be probed by a proper analysis of the rapidly changing phase of vacuum oscillations due to the eccentricity of the earth's orbit about the sun. For the case of maximal vacuum mixing, a kind of Fourier analysis of expected data for one year's time could uniquely pick out Delta m^2 if it lies in the region ~10^{-10} - 6 X 10^{-9} (eV)^2.

hep-ph↗
arXiv2001

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

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.

nucl-th↗
arXiv2001

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.

physics.atom-ph↗
arXiv1997

Exact Dirac equation calculation of ionization and pair production induced by ultrarelativistic heavy ions

An exact solution of the time-dependent Dirac equation for ionization and pair production induced by ultrarelativistic heavy ion collisions is presented. Exact transition probabilities, equivalent to those that would be obtained in an untruncated basis coupled channels calculation, are presented. Exact bound-electron positron pair production probabilities are calculated to be mostly smaller than those calculated with the same potential in perturbation theory at impact parameters small enough for differences to occur.

physics.atom-ph↗
arXiv1996

Modeling Cluster Production at the AGS

Deuteron coalescence, during relativistic nucleus-nucleus collisions, is carried out in a model incorporating a minimal quantal treatment of the formation of the cluster from its individual nucleons by evaluating the overlap of intial cascading nucleon wave packets with the final deuteron wave function. In one approach the nucleon and deuteron center of mass wave packet sizes are estimated dynamically for each coalescing pair using its past light-cone history in the underlying cascade, a procedure which yields a parameter free determination of the cluster yield. A modified version employing a global estimate of the deuteron formation probability, is identical to a general implementation of the Wigner function formalism but can differ from the most frequent realisation of the latter. Comparison is made both with the extensive existing E802 data for Si+Au at 14.6 GeV/c and with the Wigner formalism. A globally consistent picture of the Si+Au measurements is achieved. In light of the deuteron's evident fragility, information obtained from this analysis may be useful in establishing freeze-out volumes and help in heralding the presence of high-density phenomena in a baryon-rich environment.

nucl-th↗
arXiv1995

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.

nucl-th↗