Observation of $ρ/ ω$ Meson Modification in Nuclear Matter

Abstract

We have measured invariant mass spectra of electron-positron pairs in the target rapidity region of 12GeV p+A reactions. We have observed a significant difference in the mass spectra below the $ω$ meson between p+C and p+Cu interactions. The difference is interpreted as a signature of the $ρ/ω$ modification at normal nuclear-matter density.

8 pages, 3 figures, submitted to Phys. Rev. Letters. all the figures changed to Postscript format, text not changed