#### Document Type

Article

#### Department/Program

Physics

#### Journal Title

PHYSICAL REVIEW LETTERS

#### Pub Date

8-10-2017

#### Volume

119

#### Issue

6

#### Abstract

The nuclear matrix element determining the pp -> de(+)v fusion cross section and the Gamow-Teller matrix element contributing to tritium beta decay are calculated with lattice quantum chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor-symmetric value of the quark masses, corresponding to a pion mass of m(pi) similar to 806 MeV. The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within 2 sigma of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated pp -> de(+)v transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be L-1,L-A = 3.9(0.2)(1.0)(0.4)(0.9) fm(3) at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.

#### Recommended Citation

Savage, Martin J.; Shanahan, Phiala E.; Tiburzi, Brian C.; Wagman, Michael L.; Winter, Frank; Beane, Silas R.; Chang, Emmanuel; Davoudi, Zohreh; Detmold, William; and Orginos, Kostas, Proton-Proton Fusion and Tritium beta Decay from Lattice Quantum Chromodynamics (2017). *PHYSICAL REVIEW LETTERS*, 119(6).

10.1103/PhysRevLett.119.062002

#### DOI

10.1103/PhysRevLett.119.062002