Charge symmetry breaking in the neutron-proton system

Abstract

Two consequences of charge symmetry breaking (CSB) in the n-p system are examined. In n-p elastic scattering, CSB nuclear forces cause a difference between the polarizations of the neutron and the proton scattered in opposite directions in the center of mass system. The expected differences in polarizations due to one-boson exchanges, particularly a photon exchange, isospin mixed mesons, and a pion (with the n-p mass difference taken into account), are computed. The calculated polarization difference is typically of the order of several tenths of a percent. In np → dπ0, the CSB of nuclear forces can be tested by measuring the asymmetry of the angular distribution of deuterons about 90° in the center of mass frame. The expected asymmetry is calculated for one-boson exchange CSB mechanisms, as in the elastic scattering. The asymmetry caused by the mixed η−π0 exchange is dominant, but all of the mechanisms contribute asymmetries with similar angular dependences. The maximum asymmetry is about 0.8 % at 0°; the average is about 0.2 %.