Measurement of invariant mass spectra of vector meson decaying in nuclear matter

Abstract

The experiment E325 has been performed at KEK PS. The data taking has been completed on February 2002. We have measured the invariant mass spectrum of e +e − pairs based on the statistics 100 times larger than our previous publication[3]. On the low-mass side of π/ω meson, an enhancement over the known hadronic sources has been observed. The obtained π/ω ratio in the spectrum is smaller than the ratio in pp interaction. This suggests that π meson mass has been modified in nuclear matter.