Abstract
Precision measurements in allowed nuclear beta decays and neutron decay are reviewed and analyzed both within the Standard Model and looking for new physics. The analysis incorporates the most recent experimental and theoretical developments. The results are interpreted in terms of Wilson coefficients describing the effective interactions between leptons and nucleons (or quarks) that are responsible for beta decay. New global fits are performed incorporating a comprehensive list of precision measurements in neutron decay, superallowed 0+→ 0+ transitions, and other nuclear decays that include, for the first time, data from mirror beta transitions. The results confirm the V-A character of the interaction and translate into updated values for Vud and gA at the 10−4 level. We also place new stringent limits on exotic couplings involving left-handed and right-handed neutrinos, which benefit significantly from the inclusion of mirror decays in the analysis.
Highlights
Information about the underlying physics at high-energies that is relevant for beta decays is condensed into a small number of Wilson coefficients, which parametrize the strength of effective interactions between nucleons, electrons, and neutrinos at low energies
The main results of this work are the constraints on the CX± Wilson coefficients using neutron and nuclear physics data, with special attention to the role played by mirror beta decays which are included in a global fit for the first time
In this paper we have discussed the constraints from nuclear beta decays on the parameters of the effective Lee-Yang Lagrangian describing the weak interactions between nucleons, electrons, and neutrinos, paying special attention to the role played by mirror decays
Summary
Nuclear beta decays probe charged-current interactions between the first generation of quarks and leptons. The central assumption is that, at the energy scale corresponding to beta decays, there is no other light degrees of freedom except for those of the SM and (eventually) the right-handed electron neutrino Given this field content, the leading order effective Lagrangian at the scale μ 2 GeV contains the following interactions relevant for beta decays. Given the experimental precision, subleading effects such as weak-magnetism and long-distance electromagnetic corrections have to be included in the SM terms These small contributions can be calculated with large accuracy for the transitions that are included in this work [1, 29,30,31]. The main results of this work are the constraints on the CX± Wilson coefficients using neutron and nuclear physics data, with special attention to the role played by mirror beta decays which are included in a global fit for the first time. In the remainder of this section we review how beta decay observables included in this work depend on the CX± Wilson coefficients
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