PARTIAL DECAY WIDTHS OF THE ϕ INTO e+e− AND K+K− PAIRS IN 12 GeV p + A REACTIONS AT KEK-PS E325
Abstract
The experiment KEK-PS E325 measured e+e− and K+K− pairs produced in 12 GeV p + A reactions, in order to search for in-medium modification of vector mesons. In the e+e− spectra, a significant excess on the low-mass side of the ϕ-meson peak is observed in the very low βγ (= p/m) region of the copper target data. On the other hand when the velocity of ϕ mesons is higher or a smaller target, carbon, is employed, the observed ϕ-meson shapes are consistent with the expected shape in vacuum, both in the e+e− and K+K− spectra. We have also compared the nuclear mass number dependence of ϕ-meson production between the e+e− and K+K− decay channels. Using these results, the first experimental limits are obtained for in-medium broadening of the partial decay widths.
