In-Medium rho0 Spectral Function Study via the 2H, 3He, 12C(gamma,pi+pi-) Reaction
Abstract
We report a helicity analysis of sub-threshold rho0 production on 2H, 3He and 12C at low photo-production energies. The results are indicative of a large longitudinal rho0 polarization (l=1, m=0) and are consistent with a strong helicity-flip production mechanism. This signature is used to extract in-medium rho0L invariant mass distributions for all three nuclei in a manner which is less model-dependent than previous measurements. The results are compared to kinematic and phenomenological models of the rho0 spectral function. The 2H and 3He data distributions support the role of N*(1520) excitation in shaping the in-medium rho0L invariant mass distribution, while the 12C distributions are consistent with quasi-free rho0L production. The data support an in-medium modification of the rho0L invariant mass distribution.
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