Subthreshold rho^0 photoproduction on 3He

• Published in: arXiv.org
• Main Authors: Collaboration, TAGX, Kagarlis, M A, Papandreou, Z, Huber, G M, Lolos, G J, Shinozaki, A, Brash, E J, Farzanpay, F, Iurescu, M, Weinerman, A, Garino, G, Maruyama, K, Konno, O, Maeda, K, Terasawa, T, Yamazaki, H, Emura, T, Hirosawa, H, Niwa, K, Yamashita, H, Endo, S, Miyamoto, K, Sumi, Y, Leone, A, Perrino, R, Maki, T, Sasaki, A, Kim, J C
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 23.11.1998
• Subjects: Photon beams; Photoproduction; Vector mesons
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.9811010

A large reduction of the rho^0 mass in the nuclear medium is reported, inferred from dipion photoproduction spectra in the 1 GeV region, for the reaction 3He(gamma,pi+ pi-)X with a 10% duty factor tagged-photon beam and the TAGX multi-particle spectrometer. The energy range covered (800 < E(gamma) < 1120 MeV) lies mostly below the free rho^0 production threshold, a region which is believed sensitive to modifications of light vector-meson properties at nuclear-matter densities. The rho^0 masses extracted from the MC fitting of the data, m*(rho^0) = 642 +/- 40, 669 +/- 32, and 682 +/- 56 MeV/c^2 for E(gamma) in the 800-880, 880-960, and 960-1040 MeV regions respectively, are independently corroborated by a measured, assumption-free, kinematical observable. This mass shift, far exceeding current mean-field driven theoretical predictions, may be suggestive of rho^0 decay within the range of the nucleonic field.