A solution to the puzzle of quenched beta-decays

A central puzzle has been that observed β-decay rates are systematically smaller than theoretical predictions. This was attributed to an apparent quenching of the fundamental coupling constant gA in the nucleus by a factor of about 0.75. The origin of this quenching is controversial and has so far eluded a first-principles theoretical understanding. This talk presents a solution to this puzzle, and shows that this quenching can be explained from two-body currents and many-body correlations. Using interactions and currents from chiral effective field theory that describe Gamow-Teller strength in light nuclei well, I will present a first principles computation of the Gamow-Teller strength in ¹⁰⁰Sn. By developing high order coupled-cluster methods we obtain a quenching factor in the range 0.73-0.85 from two-body currents which depends somewhat on the employed Hamiltonian. Our results are consistent with experimental data, including the pioneering measurement for ¹⁰⁰Sn [1,2]. These theoretical advances have been enabled by systematic effective field theories combined with powerful quantum many-body techniques and ever increasing computational power. 

[1] Hinke, C. B. et al., Nature 486, 341-345 (2012). 

 [2] Batist, L. et al. Eur. Phys. J. A 46, 45-53 (2010).