Parity-violating interaction effects in the np system

作者：Schiavilla R^*; Carlson J; Paris M

来源：Physical Review C, 2004, 70(4): 044007.

DOI：10.1103/PhysRevC.70.044007

We investigate parity-violating observables in the np system, including the longitudinal asymmetry and neutron-spin rotation in np elastic scattering, the photon asymmetry in np radiative capture, and the asymmetries in deuteron photodisintegration d(gamma,n)p in the threshold region and electrodisintegration d(e,e('))np in quasielastic kinematics. To have an estimate of the model dependence for the various predictions, a number of different, latest-generation strong-interaction potentials-Argonne v(18), Bonn 2000, and Nijmegen I-are used in combination with a weak-interaction potential consisting of pi-, rho-, and omega-meson exchanges-the Desplanques-Donoghue-Holstein (DDH) model. The complete bound and scattering problems in the presence of parity-conserving, including electromagnetic, and parity-violating potentials are solved in both configuration and momentum space. The issue of electromagnetic current conservation is examined carefully. We find large cancellations between the asymmetries induced by the parity-violating interactions and those arising from the associated pion-exchange currents. In the np capture, the model dependence is nevertheless quite small, because of constraints arising through the Siegert evaluation of the relevant E-1 matrix elements. In quasielastic electron scattering these processes are found to be insignificant compared to the asymmetry produced by gamma-Z interference on individual nucleons. These two experiments, then, provide clean probes of different aspects of weak-interaction physics associated with parity violation in the np system. Finally, we find that the neutron-spin rotation in np elastic scattering and asymmetry in deuteron disintegration by circularly polarized photons exhibit significant sensitivity both to the values used for the weak vector-meson couplings in the DDH model and to the input strong-interaction potential adopted in the calculation. This reinforces the conclusion that these short-ranged meson couplings are not in themselves physical observables; rather, the parity-violating mixings are the physically relevant parameters.

• 出版日期2004-10