Probing vector meson properties in nuclei with photo-production of the neutral pion

Abstract

The nuclear contribution to forward angle photo-production of the π 0-meson is calculated using an effective lagrangian derived from the triangle anomaly. This lagrangian mediates the interaction of a pion, a photon, and a vector meson mean field. The vector meson mass, m v, and the pion decay constant, f π , are assumed to have a density-dependence given by m v ∗ ( r)/m v = f π ∗( r)/f π = 1−λ( r)/ϱ NM) . The nuclear and Coulomb contributions to pion photo-production yield a cross-section which is sensitive to the properties of the vector meson in nuclear matter. In particular, both the overall strength of the vector meson mean field which is parameterized by g v and the density-dependence of the meson field which is parameterized by λ can be extracted.