Precision Analysis of Neutron Beta Decays to Order 10^-5

The work under the problems of this project should provide a substantial improvement of our knowledge about strong lowenergy interactions and their influence on the weak decay processes. An importance of such an influence was pointed out by Weinberg in 1956 year. As has been shown by Sirlin in 1967 year, strong lowenergy interactions play an important but passive role in the neutron beta decay in the analysis of the outer radiative corrections and inner bremsstrahlung to first order in the finestructure constant. Indeed, they are important for gauge invariance of these corrections but do not depend on the electron energy, that allows to remove their contributions by renormalization of the Fermi and axial coupling constants. A nontrivial role of strong lowenergy interactions for gauge invariance of the radiative corrections to second order of the finestructure constant, which goes beyond simple contributions independent of the electron energy, has been pointed out by Ivanov with co-workers (Ivanov2017). By example of the rate of the neutron radiative beta decay to second order of the finestructure constant, there has been shown that the contributions of strong lowenergy interactions are not only important for gauge invariance of radiative corrections but these contributions depend also on the electron and photon energies and can be observed experimentally by measuring electron and proton energy spectra and angular distributions with uncertainties of a few parts in 10-5. The calculation of the radiative corrections of the first order in the finestructure constant and nexttoleading order in the large nucleon mass expansion, and the nexttonexttoleading order corrections, caused by the weak magnetism and proton recoil, should provide a completion of the analysis of corrections of order 10-5 and a new level of understanding of the role of the weak magnetism in the neutron beta decay in particular and probably in weak decay processes in general. Thus, the results, which should be obtained during the work on this project, i) should improve substantially our knowledge of the role of strong lowenergy interactions in weak decay processes and ii) should be a new impetus for the development of experimental technologies and methods, providing new higher levels of experimental accuracy for experimental tests of the Standard Model. The use of the renormalizable smodel for the description of strong interactions, which is equivalent to the current algebra, should to realize the aim of the project at the same confidence level as Sirlins results.

This project makes an important contribution to the theoretical aspects of beta decay of neutrons, in particular to the analysis of the so-called correlation coefficients, in order to search for extensions of the Standard Model of elementary particles. The work focuses on detailed predictions of beta-decay observables that can be tested experimentally to find new physics. For example, our group investigates the effects of asymmetries in beta decay of neutrons on fundamental symmetries and their possible violation in new, hypothetical interactions beyond the Standard Model. A key aspect of the project was to calculate the theoretical predictions of the Standard Model so precisely that a comparison between theory and experiment can be made at a new level using the experimental possibilities of the new PERC measuring station at the Heinz Maier-Leibnitz Zentrum in Munich. The project will also contribute to solving the neutron lifetime problem. This problem, often referred to as the "neutron lifetime puzzle", is one of the open questions in nuclear and particle physics. It is about the fact that the measured lifetime of the free neutron shows different values depending on the experimental method, which leads to a discrepancy of about 8-10 seconds. Working on the project, Ben Koch has proposed an intriguing solution to the neutron lifetime puzzle that addresses the persistent discrepancy between the "bottle" and "beam" measurement methods. His hypothesis states that free neutrons exist not only in the ground state, but possibly in a mixture of excited quantum states. These states, which differ in their energy and decay properties, could explain the systematic difference of eight seconds observed between the bottle method (880 seconds) and the beam method (888 seconds). The theory is testable: Experiments could identify these hypothetical excited neutron states and quantify their influence on the decay lifetime.