Tritium β decay and proton-proton fusion in pionless effective field theory

Abstract

The Gamow-Teller and Fermi matrix elements, 〈GT〉 and 〈F〉, respectively, for tritium β decay are calculated to next-to-leading order (NLO) in pionless effective field theory in the absence of Coulomb interactions and isospin violation giving the leading order predictions 〈GT〉0=0.9807 and 〈F〉0=1. Using an experimentally determined value for the tritium β decay GT matrix element, the two-body axial current low energy constant is fixed at NLO yielding L1,A=6.01±2.08fm3 at the renormalization scale of the physical pion mass, which agrees with predictions based on naive dimensional analysis. The impact of L1,A on proton-proton fusion is also discussed. Finally, the consequences of Wigner-SU(4) spin-isospin symmetry are considered for the Gamow-Teller matrix element. Published by the American Physical Society 2024