A Gamow–Teller transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin S = 1 , leading to an angular momentum change Δ Δ J = 0 , ± ± 1 between the initial and final states of the nucleus (assuming an allowed transition). In this case, the nuclear part of the operator is given by O G T = G A ∑ ∑ a σ σ ^ ^ a τ τ ^ ^ a ± ± with G A the weak axial-vector coupling constant, and σ σ the spin Pauli matrices, which can produce a spin-flip in the decaying nucleon.