Realistic equivalent-photon yields in heavy-ion collisions

Heavy-ion collisions are a potentially prolific source of γγ collisions at very-high-energy colliders. However, their utility is limited to events in which the nuclei miss each other. The Weizs\"acker-Williams approximation in impact-parameter space is used to evaluate the consequent reduction in photon flux below that obtained by including the effect of the size of the nucleus only through the elastic form factor. The effective luminosity (τZ⁴)dLdτ is shown for all relevant circumstances to be a function of the single variable z=mRγ, where m is the mass of the created system, R is the nuclear radius, and γ is the center-of-mass-system Lorentz factor of each nucleus. A graph and a simple parametrization are given of (τL₀)dLdτ as a function of z. The effective cross section for production of a Higgs boson with a mass of 100 (150) GeV using Pb-Pb-generated γγ collisions is reduced by a factor of roughly 1/2.4 (1/3) at the Superconducting Super Collider and a factor of 1/4.6 (1/7) at the CERN Large Hadron Collider by the exclusion of events in which the nuclei collide.