Parity-violating interaction effects in thenpsystem

Abstract

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 photo-disintegration d( γ, n)p in the threshold region and electrodisintegration d( e, e ′ )np in quasi-elastic 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 π-, ρ-, and ω-meson exchanges-the model known as DDH. The complete bound and scattering problems in the presence of parity-conserving, including electromagnetic, and parity-violating potentials is 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 quasi-elastic electron scattering these processes are found to be insignificant compared to the asymmetry produced by γ-Z interference on individual nucleons. These two experiments, then, provide clean probes of different aspects of weakinteraction 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 1 mixings are the physically relevant parameters. 21.30.+y, 25.40.Cm

Parity violation in radiative neutron capture on the deuteron

“…Therefore, one can see a number of reasons why PV threebody radiative capture processes should be more sensitive to a short distance dynamics than PV effects in three-body elastic scattering. It should be noted that even in the two-body case, circular photon polarization P γ in n-p radiative capture, which is not dominated by one-pion exchange, shows stronger model dependence [36] than the asymmetry a γ n , which defined by the one-pion exchange mechanism.…”

“…Therefore, it is useful to re-analyze the two-body n-p capture process, for which the large model dependence for the circular polarization of photons, P γ , was reported in [36].…”

Measurement of parity-violatingγ-ray asymmetry in the capture of polarized cold neutrons on protons

“…In this model the only significant contribution to the NPDGamma asymmetry comes from weak pion exchange. The relation between the measured asymmetry and the DDH weak meson couplings is [5,11,[38][39][40][41] …”

“…These results are consistent with the theoretically estimated size of the asymmetry in the DDH model ≈ 5 × 10 −8 . Since the deuteron bound state and low energy scattering states are dominated by the long-range components of the strong NN interaction, which are well understood experimentally, the relation between the asymmetry and the weak coupling in either model mentioned above is stable against small variations in NN strong interaction parameters, which primarily affect the short-range components [5,29,31,37,38].…”

Parity and time-reversal violation in A=2-4 nuclei

“…In particular, recently extensive analysis of the parity violation in the neutronproton system [20] and for the longitudinal asymmetry in proton-proton elastic scattering has been performed by Schiavilla et al [22] and very recently by de Vries et al [21]. In these papers, different realistic strong interaction Hamiltonians have been employed in conjunction with the parity-violating DDH potential.…”