Observation of ρ/ ω Meson Modification in Nuclear Matter
K. Ozawa, H. En'yo, H. Funahashi, M. Kitaguchi, M. Ishino, H. Kanda, S. Mihara, T. Miyashita, T. Murakami, R. Muto, M. Naruki, F.Sakuma, H. D. Sato, T. Tabaru, S. Yamada, S. Yokkaichi, Y. Yoshimura, J. Chiba, M. Ieiri, M. Nomachi, O. Sasaki, M. Sekimoto, K. H. Tanaka, H. Hamagaki
Abstract
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.