Ab initio calculation of the ³He(α,γ)⁷Be astrophysical S factor

The ³He(α,γ)⁷Be reaction is an important part of ongoing processes occuring in all stars like our very own sun. In the fusion reaction network of the sun, the ³He(α,γ)⁷Be reaction is key to determining the ⁷Be and ⁸B neutrino fluxes resulting from the pp-II chain . In standard solar model (SSM) predictions of these neutrino fluxes, the low-energy ³He(α,γ)⁷Be S factor, S₃₄(E), is the largest source of uncertainty from nuclear input. The SSM uses S₃₄(E) near the Gamow peak energy, roughly 18 keV, which cannot be experimentally measured since the Coulomb force between ³He and ⁴He suppresses the fusion reaction at such low energies. Theoretical calculations are needed to guide the extrapolation to the solar energies of interest. To this end, I will present ab initio calculations of the ³He(α,γ)⁷Be reaction using the no-core shell model with continuum starting from two- and three-nucleon chiral interactions. To demonstrate that the NCSMC provides an accurate S factor, I will also compare NCSMC ³He + ⁴He elastic-scattering cross sections with those recently measured by the SONIK collaboration.