Velocity dependence of the mass modifications of ρ and ω mesons in 12 GeV p + A reactions

This study measured the invariant mass spectra of ρ and ω mesons in the e+e− decay channel for 12 GeV (12.9 GeV/c) p + C and p + Cu reactions (√sNN=5.1 GeV) at the KEK 12-GeV Proton Synchrotron. The measured spectra were divided into three βγ regions to examine their velocity dependence. Across all regions, significant excesses were observed on the low-mass side of the ω meson peak, beyond the contributions of known hadronic sources, in the data of the C and Cu targets. Model calculations were subsequently performed to evaluate the magnitudes of the mass modifications of ρ and ω mesons.