Vector Mesons in Cold Nuclear Matter

The attenuation of vector mesons in cold nuclear matter is studied through the mechanism of incoherent photoproduction off complex nuclei. The latter is described via the time-dependent multi-collisional Monte Carlo (MCMC) intranuclear cascade model. The results for the transparency ratios of ω mesons reproduce previous measurements of CB-ELSA/TAPS with an inelastic ωN cross section around 40 mb for ρω ~ 1.1 GeV/c. The corresponding in-medium width (nuclear rest frame) is extracted dinamically from the algorithm and depends on the average nuclear density pN and target nucleus: ~ 49.2 MeV/c2 for carbon (pN 0.114 far−3) and ~ 77.3 MeV/c2 for lead (pN 0.137 far−−3). The calculations fail to reproduce the huge absorption observed at JLab assuming the same inelastic cross section and the discrepancy between the two experiments remains a challenge.