Modification of {$\mit \Delta $}(1232) in the Neutrino Nucleus Reaction

Abstract

The remarkable observations in the pion induced and charge exchange reactions on a nucleus are the significant shift and broadening of the $\Delta (1232)$-peak relative to free pion nucleon scattering. For the forward going massless leptons, the weak process $(\nu_l,l)$ on a nucleon, according to Adler's partially conserved axial current theorem, is connected to the pion nucleon scattering. This mechanism is also applicable to the nucleus. Therefore, the modification of the $\Delta$-peak in a nucleus can be seen in the $(\nu_l,l)$ reaction since it is connected to the pion nucleus scattering. To investigate this issue quantitatively, the double differential cross sections of the forward going ejectile $l$ energy distribution in the $(\nu_l,l)$ reaction are calculated in the $\Delta$-excitation region for both proton and nucleus. The measured pion nucleon and pion nucleus scattering cross sections in the quoted energy region are used in these reactions as input. Since the $(\nu_l,l)$ reaction is connected to the pion induced scattering, the features of the previous reaction is shown analogous to those of the later.