Exclusive production of rho^0 rho^0 pairs in gamma-gamma collisions at RHIC

Abstract

We discuss exclusive electromagnetic production of two neutral $\rho$ mesons in coherent photon-photon processes in ultrarelativistic heavy-ion collisions. The cross section is calculated in the equivalent photon approximation (EPA). Both uncertainties of the flux factors and photon-photon cross sections are discussed in details. We show that inclusion of precise charge densities in nuclei is essential for realistic evaluations of the nuclear photon-photon cross sections. We find that the cross section, especially with realistic flux factors, is sensitive to low energy in the subsystem $\gamma \gamma \to \rho^0 \rho^0$. The experimental data for the $\gamma \gamma \to \rho^0 \rho^0$ cross section extracted from $e^+ e^-$ collisions are parametrized and used to estimate the nucleus-nucleus cross section. In addition, we include vector-dominance-model(VDM)--Regge contribution which becomes important at large photon-photon energy. Large nuclear cross sections are obtained. We discuss a possibility of focusing on the large-energy component. We find that both $\rho^0$ mesons are produced predominantly at midrapidities and could be measured by the STAR collaboration at RHIC.