Subthreshold 0 photoproduction on 3 He
/ Authors
T. C. M. A. Kagarlis, Z. Papandreou, G. Huber, G. Lolos, A. Shinozaki, E. Brash, F. Farzanpay, M. Iurescu, A. Weinerman, G. Garino
and 17 more authors
K. Maruyama, O. Konno, K. Maeda, T. Terasawa, H. Yamazaki, T. Emura, H. Hirosawa, K. Niwa, H. Yamashita, S. Endo, K. Miyamoto, Y. Sumi, A. Leone, R. Perrino, T. Maki, A. Sasaki, J. C. Kim
/ Abstract
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.