The invariant mass spectra of e+e- pairs produced in 12 GeV p+A reactions are measured at the KEK Proton Synchrotron. We observed a significant enhancement over the known hadronic sources on the low-mass side of the ω meson peak for C and Cu data. The 95% CL allowed parameter regions for ρ/ω ratio are obtained as ρ/ω< 0.15 and ρ/ω< 0.31 for C and Cu targets, respectively. As for the meson, the data obtained with a Cu target revealed a significant excess on the low-mass side of the meson peak mainly in the βγ < 1.25 region.
|Journal||Journal of Physics G: Nuclear and Particle Physics|
|Publication status||Published - 2007 Aug 1|