Medium Modi cation on Vector Mesons Observed in 12 GeV p + A Reactions

Abstract

Experimental study of the e+e− → π+π−π0 reaction by SND detector in the energy range s = 0.42 - 1.38 GeV AIP Conf.Abstract. The invariant mass spectra of e + e − pairs produced in 12 GeV p+A reactions are measured at the KEK-PS. We observed a significant enhancement over the known hadronic sources on the low-mass side of the ω meson peak. The 95 % C.L. allowed parameter regions for ρ/ω ratio are obtained as ρ/ω < 0.15 and ρ/ω < 0.31 for C and Cu targets, respectively. As for the φ meson, the data obtained with a Cu target revealed a significant excess on the low-mass side of the φ meson peak mainly in the β γ φ < 1.25 region.