Abstract
Since the emission of γ grays unavoidably accompanies β decay, the final state after the β decay of a neutron includes a photon along with a proton, an electron, and an antineutrino, i.e., four particles, rather than three. Therefore, when only the electron and proton momenta are detected and the γ-ray momentum is not detected in an experiment, the antineutrino momentum cannot be uniquely reconstructed, and only its mean value over a γ-ray momentum distribution determined from corresponding calculations can be considered. The γ grays are significant for finding the asymmetry parameter B of the antineutrino angular distribution from experiments on the β decay of polarized neutrons, where the electron momentum p directed along the x axis and the projection of the proton momentum P x onto the x axis are detected, and the neutron polarization vector ξ is parallel or antiparallel to x. Since the γ rays are not detected in such experiments, the antineutrino kinematics are not uniquely specified by the observables p and P x and can be reconstructed only on the average, so that the antineutrino momentum distribution averaged over a γ-ray momentum distribution is considered. Thus, the exact value of B cannot be obtained from these experiments, but the true value of B can be estimated on the average by considering the mean (most likely) value 〈B〉 and the dispersion (rms deviation) ΔB. The unavoidable uncertainty in the estimate of B amounts to several percent and is thus significant for present-day experiments, which are intended to obtain the value of B to a very high accuracy of ∼ (0.1–1)%. If electromagnetic interactions are taken into account, measurements of the electron and proton momentum distributions can also be used to obtain g A, i.e., the axial β-decay amplitude, to high accuracy.
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Zh. Éksp. Teor. Fiz. 116, 1505–1522 (November 1999)
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Bunatyan, G.G. Investigation of the antineutrino angular distribution in experiments on the β decay of polarized neutrons. J. Exp. Theor. Phys. 89, 811–820 (1999). https://doi.org/10.1134/1.558919
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DOI: https://doi.org/10.1134/1.558919