Parity violation asymmetry in nucleon-nucleon scattering

Abstract

We evaluate the helicity dependence of the differential and total cross section for the scattering of longitudinally polarized neutrons on unpolarized neutrons at E = 45 MeV following a SIN experiment and at E = 230 MeV in anticipation of an experiment at TRIUMF. (Both experiments study proton-proton scattering of course, namely p + p→ p+ p ). Calculations are based on the Desplanques, Donoghue and Holstein (DDH) theory for the weak NN interaction and on the Paris potential for the strong NN force. The results can be expressed as a linear combination in the (DDH) weak parameters h ρ 0, h ρ 2 and h ω 0, corresponding to exchanges of isoscalar ρ −, isotensor ρ −, and isoscalar ω − mesons, respectively. For the asymmetry in the total cross section we have found, using DDH suggested “best values”, A z (45 MeV) = −2.62 × 10 −7 and A z (230 MeV) = 0.07 × 10 −7. The small value of A z at 230 MeV is due to a sign change in the differential asymmetry. As for the asymmetry in the differential cross section we notice that even at the lower energy E = 45 MeV, the asymmetry in the differential cross section deviates from isotropy, since J > 0 weak amplitudes cannot be neglected.