First observation of ϕ-meson mass modification in nuclear medium

✍ Scribed by 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; M. Nomachi; K. Ozawa; F. Sakuma; O. Sasaki; H.D. Sato; M. Sekimoto; T. Tabaru; K.H. Tanaka; M. Togawa; S. Yamada; S. Yokkaichi; Y. Yoshimura

• Publisher: Elsevier Science
• Year: 2006
• Tongue: English
• Weight: 218 KB
• Volume: 774
• Category: Article
• ISSN: 0375-9474
• DOI: 10.1016/j.nuclphysa.2006.06.123

✦ Synopsis

We have measured e + e -invariant mass spectra in 12 GeV p + A interactions at the KEK Proton-Synchrotron. The aim of the experiment is to detect possible in-medium modification of vector mesons at normal nuclear density. We used carbon and copper targets to study the nuclear size dependence of the e + e -invariant mass spectra. A significant enhancement on the low-mass side of the φ meson peak was observed in the low βγ region (βγ φ < 1.25) in the copper data. On the other hand, in the higher βγ region ( βγ φ > 1.25 ), both the spectral shapes obtained from carbon and copper targets were consistent with the expected one from the simulation. This observation is consistent with a picture of the φ modification in a nucleus, i.e. normal nuclear density, because such an effect should be visible only for slowly moving mesons produced in a larger nucleus.