The Gold Flashlight: Coherent Photons (and Pomerons) at RHIC

Abstract

The Relativistic Heavy Ion Collider (RHIC) will be the first heavy ion accelerator energetic enough to produce hadronic final states via coherent \gamgam, \gampom, and \pompom interactions. Because the photon flux scales as $Z^2$, up to an energy of about $γ\hbar c/R\approx 3$ GeV/c, the \gamgam\ interaction rates are large. RHIC $γP$ interactions test how Pomerons couple to nuclei and measure how different vector mesons, including the $J/ψ$, interact with nuclear matter. $PP$ collisions can probe Pomeron couplings. Because these collisions can involve identical initial states, for identical final states, the \gamgam, \gampom, and \pompom channels may interfere, producing new effects. We review the physics of these interactions and discuss how these signals can be detected experimentally, in the context of the STAR detector. Signals can be separated from backgrounds by using isolation cuts (rapidity gaps) and $p_\perp$. We present Monte Carlo studies of different backgrounds, showing that representative signals can be extracted with good rates and signal to noise ratios.