On the structure of the correlation coefficients S(E_e) and U(E_e) of the neutron beta decay

TL;DR

This paper analyzes the structure of correlation coefficients S(E_e) and U(E_e) in neutron beta decay within the Standard Model, including radiative and recoil corrections, and explores potential beyond Standard Model contributions.

Contribution

It provides a detailed theoretical analysis of the correlation coefficients' structure, incorporating radiative, recoil, and BSM effects in neutron beta decay.

Findings

Calculated SM radiative and recoil corrections to correlation coefficients.

Identified possible BSM contributions via phenomenological coupling constants.

Enhanced understanding of neutron decay correlations within and beyond the Standard Model.

Abstract

In the standard effective V - A theory of low-energy weak interactions (i.e. in the Standard Model (SM)) we analyze the structure of the correlation coefficients S(E_e) and U(E_e), where E_e is the electron energy. These correlation coefficients were introduced to the electron-energy and angular distribution of the neutron beta decay by Ebel and Feldman ( Nucl. Phys. 4, 213 (1957)) in addition to the set of correlation coefficients proposed by Jackson et al. (Phys. Rev. 106, 517 (1957)). The correlation coefficients $S(E_e)$ and $U(E_e)$ are induced by simultaneous correlations of the neutron and electron spins and electron and antineutrino 3-momenta. These correlation structures do no violate discrete P, C and T symmetries. We analyze the contributions of the radiative corrections of order O(alpha/pi), taken to leading order in the large nucleon mass m_N expansion, and corrections of order O(E_e/m_N), caused by weak magnetism and proton recoil. In addition to the obtained SM corrections we calculate the contributions of interactions beyond the SM (BSM contributions) in terms of the phenomenological coupling constants of BSM interactions by Jackson et al. (Phys. Rev. 106, 517 (1957)) and the second class currents by Weinberg (Phys. Rev. 112, 1375 (1958)).