In-medium modifications of the ω meson near the production threshold

Abstract

The in-medium properties of the ω meson were investigated at the MAMI-C electron accelerator using the Crystal Ball/TAPS detector system to identify ω mesons through their ω → π 0 γ decay channel. Two solid targets (C, Nb) and a LH2 target as a reference have been used. In the energy range 900 to 1300 MeV the ω lineshapes for the different nuclei are compared and a broadening of the ω signal for the niobium target is observed in comparison to the liquid-hydrogen target. In a second analysis the ω momentum distributions for the solid targets are determined for 50 MeV/c wide bins. For both analyses a comparison to transport calculations shows that the data are consistent with an in-medium modification by collisional broadening, as observed by transparency ratio measurements.