Weak Transitions in Light Nuclei

Abstract

Nuclei are used for high-precision tests of the Standard Model and for studies of physics beyond the Standard Model. Without a thorough understanding of nuclei, we will not be able to meaningfully interpret the growing body of experimental data nor will we be able to disentangle new physics signals from underlying nuclear effects. This calls for accurate calculations of nuclear structure and reactions. In this work, we focus on electroweak decays in nuclei with mass number A ≤ 10 and report on ab initio Quantum Monte Carlo calculations of reduced matrix elements entering beta decays and electron captures in nuclei with mass number A ≤ 10. The many-body wave functions are calculated using selected Norfolk two-and three-nucleon potential models and associated one-and two-body axial currents at tree-level obtained from a chiral effective field theory with pions, nucleons, and. The agreement with the experimental data is satisfactory except for transitions in A = 8 nuclei. In this specific case, the theory significantly underpredicts the experimental data, which indicates the need of further improvements in the corresponding nuclear wave functions. In this study, emphasis is placed on the contributions of two-body axial currents that are carefully analyzed using two-body transition densities. This allow us to study the spatial distribution and short-range behavior of two-body dynamics. In particular, the transition densities when scaled to peak at 1.0 exhibit universal short-range behavior across the considered nuclei, while they differ in the long-range tails.

Muon capture on deuteron using local chiral potentials

“…This local chiral framework has been used to calculate energies [23] and charge radii [24] and various electromagnetic observables in light nuclei, as the charge form factors in A = 6, 12 [24] and the magnetic structure of few-nucleon systems [22]. It has also been used to study weak transitions in light nuclei [25,26], the muon captures on A = 3, 6 nuclei [27], neutrinoless double β-decay for A = 6, 12 [28] and the β-decay spectra in A = 6 [29], and, finally, the equation of the state of pure neutron matter [30,31]. However, the use of the Norfolk potentials to study the muon capture on a deuteron and the pp reaction is still lacking.…”