A large reduction of the ρ0 mass in the nuclear medium is reported, inferred from dipion photoproduction spectra in the 1 GeV region, for the reaction 3He(γ, π+π-)X with a 10% duty factor tagged-photon beam and the TAGX multiparticle spectrometer. The energy range spanned (800≤Eγ≤1120 MeV) lies mostly below the free-ρ0 production threshold, a region which is believed to be sensitive to modifications of light vector-meson properties at nuclear-matter densities. The values of the ρ0 mass extracted from the Monte Carlo fitting of the data were m*ρ0=642±40, 669±32, and 682±56 MeV/c2 for Eγ in the 800-880, 880-960, and 960-1040 MeV regions, respectively. These values were independently corroborated in a qualitative fashion by a measured, assumption-free, kinematical observable. This mass shift, far exceeding current mean-field-driven theoretical predictions, may be suggestive of a nucleonic source of modification or of a bound state in the nuclear mean field.
|Number of pages||2268287|
|Journal||Physical Review C - Nuclear Physics|
|Publication status||Published - 1999 Aug|
ASJC Scopus subject areas
- Nuclear and High Energy Physics