Evidence for in-medium modification of the meson at normal nuclear density

R. Muto, J. Chiba, H. En'Yo, Y. Fukao, H. Funahashi, H. Hamagaki, M. Ieiri, M. Ishino, H. Kanda, M. Kitaguchi, S. Mihara, K. Miwa, T. Miyashita, T. Murakami, T. Nakura, M. Naruki, K. Ozawa, F. Sakuma, O. Sasaki, M. SekimotoT. Tabaru, K. H. Tanaka, M. Togawa, S. Yamada, S. Yokkaichi, Y. Yoshimura

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150 Citations (Scopus)


Invariant mass spectra of e+e- pairs have been measured in 12 GeV p+A reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of e+e- invariant mass distributions. A significant excess on the low-mass side of the meson peak is observed in the low βγ(=β/1-β2) region of mesons (βγ<1.25) with copper targets. However, in the high βγ region (βγ>1.25), spectral shapes of mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on ρ/ω modification, this study has experimentally verified vector meson mass modification at normal nuclear density.

Original languageEnglish
Article number042501
JournalPhysical review letters
Issue number4
Publication statusPublished - 2007
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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