Observation of $\rho / \omega$ Meson Modification in Nuclear Matter
  We have measured invariant mass spectra of electron-positron pairs in the target rapidity region of 12GeV p+A reactions. We have observed a significant difference in the mass spectra below the $\omega$ meson between p+C and p+Cu interactions. The difference is interpreted as a signature of the $\rho/\omega$ modification at normal nuclear-matter density. 
K. Ozawa, H. En'yo, H. Funahashi, M. Kitaguchi, M. Ishino, H. Kanda,   S. Mihara, T. Miyashita, T. Murakami, R. Muto, M. Nar...