Ab initio asymptotic normalizations of ⁷Be and ⁷Li states

Asymptotic normalization coefficients (ANCs) are crucial parameters for models of direct capture reactions, where they can embody constraints derived from experiment or many-body calculations. Here we report ab initio calculations of ANCs for breakup of 7Be and 7Li states into an alpha particle and a 3He or 3H nucleus using the variational Monte Carlo (VMC) method. Previous VMC calculations of these ANCs required computing the spectroscopic overlap of a state onto a cluster configuration, and then reading the ANC from the long-range tail of the overlap; this was problematic because the tail is difficult to compute well in VMC. Here we compute ANCs from an integral relation that folds the wave function with the short-ranged nucleon-nucleon potential, yielding a short-ranged integral. The resulting ANCs are then based on the most accurately-computed parts of the wave function. We report ANCs for the bound states of 7Be and 7Li, which are important for reactions in the Sun and the Big Bang, as well as partial widths of narrow unbound states. This is the first application of integral relations to cluster-separation ANCs in the quantum Monte Carlo context.