Experimental Signature of Medium Modifications for rho and omega Mesons in the 12 GeV p + A Reactions

Abstract

The invariant mass spectra of e+e- pairs produced in 12-GeV proton-induced nuclear reactions are measured at the KEK Proton-Synchrotron. On the low-mass side of the omega meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.

4 pages, 3 figures, Version accepted for Physical Review Letter

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