ρ0 meson in the nucleus

Abstract

For the mass of the hadrons in vacuum, there are several types of theoretical calculations, such as, the constituent-quark models, the bag models, and the Lattice models. A direct way is to determine the mass of the hadron, which decays in nuclear medium by constructing the invariant mass from the measurements of the decayed particle momenta. A mass-shifted peak structure is the signal of the modification. This is a direct experimental determination of the p0 meson mass in nuclear medium. Theoretically predicted mass modification of the p0 meson in the 3He nucleus is tested by a tagged-photon experiment at Tokyo. Coherently produced p0 mesons observed have the vacuum mass and the vacuum width, and these facts confirm no mass modification in the coherent production mechanism. Incoherently produced mesons have the mass spectrum that is consistent with an assumption that the p0 meson mass reduction by 15 %.