Experimental Signature of Medium Modifications for rho and omega Mesons   in the 12 GeV p + A Reactions
  The invariant mass spectra of e+e- pairs produced in 12-GeV proton-induced nuclear reactions are measured at the KEK Proton-Synchrotron. On the low-mass side of the omega meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted. 
M. Naruki, H. Funahashi, Y. Fukao, M. Kitaguchi, M. Ishino, H. Kanda,   S. Mihara, T. Miyashita, K. Miwa, T. Murakami, T. Na...