Helicity signatures in subthreshold ρ0 production on nuclei

Abstract We report a helicity analysis of subthreshold ρ 0 production on 2 H and 12 C nuclei at low photo-production energies and large | t |. The results are indicative of a large longitudinal ρ 0 polarization ( l =1, m =0) and are consistent with a strong helicity-flip mechanism of ρ 0  production. The analysis is model-independent and the resulting helicity versus invariant mass distributions are consistent with the mass shift reported from our earlier 3 He experiments.