The in-medium effects on the neutrino reaction in dense matter

Abstract

The nucleon form factors in free space are usually thought to be modified when a nucleon is bound in a nucleus or immersed in a nuclear medium. We investigated effects of the density-dependent axial and weak-vector form factors on the electro-neutrino (Ve) and anti-electro-neutrino (V¯e) reactions with incident energy Eν ≤ 80 MeV via neutral current (NC) and charged current (CC) for a nucleon in a nuclear medium or ¹²C. For the density-dependent form factors, we exploited the quark-meson-coupling (QMC) model, and apply them to the Ve and V¯e induced reactions by NC and CC. In CC reaction, about 5 % decrease of the electro neutrino Ve) reaction cross section on the nucleon is shown to be occurred in normal density, ρ =ρo ∼ 0.15fm‾³, and also about 5 % reduction of total νe cross section on ¹²C is obtained by the modification of the weak form factors for bound nucleons. Density effects for both cases are relatively small, but they are as large as the effect by the Coulomb distortion of outgoing leptons in the ν-reaction. However, density effects in the anti-electro neutrino (ν¯e) reaction reduced significantly about 30 % the cross sections for both the nucleon and 12C cases. For NC, about 12 % decrease of the total cross section by the νe reaction on the nucleon is obtained at normal density, ρ =ρ0 ∼ 0.15fm¯³, as well as about 18 % reduction of the total νe cross section on ¹²C, by the modification of the weak form factors of the bound nucleon. However, similarly to the CC reaction, effects of the nucleon property change in the V¯e reaction reduce significantly the cross sections about 30 % for the nucleon in matter and 12C cases. In this talk, we address that such a large asymmetry in the V¯e cross sections in both reactions is originated from the different helicities of V¯e and Ve.