Inclusive ω photoproduction from nuclei and ω in the nuclear medium

Abstract

With the aim of extracting information on the shift of the ω mass in the nuclear medium we analyze data obtained at ELSA from where claims for evidence of a mass shift of the ω have been made. We develop a Monte Carlo simulation code which takes into account the possible reactions in the experimental set-up of (γA --> π(0)γX) in the vicinity of the ω production region with subsequent ω --> π(0)γ decay. We compare our results with experiment for the distribution of π(0)γ invariant masses and conclude that the distribution is compatible with an enlarged ω width of about 90 MeV at nuclear-matter density and no shift in the mass. This change in the width would be compatible with the preliminary results obtained from the transparency ratio in the A-dependence of ω production. The discrepancy of the present conclusions with former claims of an evidence for a shift of the ω mass stems from a different choice of background which is discussed in the paper.