The Q^2-Dependence of Nuclear Transparency for Exclusive ${\rho }^0$ Production

Abstract

Exclusive coherent and incoherent electroproduction of the ${\rho }^0$ meson from ${}^1$H and ${}^{14}$N targets has been studied at the HERMES experiment as a function of coherence length ($l_c$), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon ($-Q^2$). The ratio of ${}^{14}$N to ${}^1$H cross sections per nucleon, known as nuclear transparency, was found to increase (decrease) with increasing coherence length for coherent (incoherent) ${\rho }^0$ electroproduction. For fixed coherence length, a rise of nuclear transparency with $Q^2$ is observed for both coherent and incoherent ${\rho }^0$ production, which is in agreement with theoretical calculations of color transparency.

5 pages, 4 figures