Ab initio calculation of the $\beta$ decay spectrum of $^6$He

Understand

We calculate the $\beta$ spectrum in the decay of $^6$He using Quantum Monte Carlo methods with nuclear interactions derived from chiral Effective Field Theory and consistent weak vector and axial currents.

• We work at second order in the multipole expansion, retaining terms suppressed by $\mathcal O(q^2/m_\pi^2)$, where $q$ denotes low-energy scales such as the reaction's $\mathcal Q$-value or the electron energy, and $m_\pi$ the pion mass.
• We go beyond the impulse approximation by including the effects of two-body vector and axial currents.
• We estimate the theoretical error on the spectrum by using four potential models in the Norfolk family of local two- and three-nucleon interactions, which have different cut-off, fit two-nucleon data up to different energies and use different observables to determine the couplings in the three-body force.