Ab initio calculation of the $^3$He$(\alpha,\gamma)^7$Be astrophysical S factor with chiral two- and three-nucleon forces

TL;DR

This study uses ab initio methods with chiral nuclear forces to calculate the astrophysical S factor for the $^3$He$(,)^7$Be reaction, crucial for stellar nucleosynthesis and solar neutrino production, providing new theoretical insights.

Contribution

First microscopic calculation of the $^3$He$(,)^7$Be reaction including three-nucleon forces, improving understanding of nuclear interactions in astrophysical processes.

Findings

Qualitative agreement with experimental S factor data.

Inclusion of experimental bound and scattering data for better accuracy.

Identified limitations in the current model's repulsion in the $1/2^+$ channel.

Abstract

The $^3$He$(\alpha,\gamma)^7$Be radiative capture reaction plays a key role in the creation of elements in stars as well as in the production of solar neutrinos, the observation of which is one of the main tools to study the properties of our sun. Since accurate experimental measurements of this fusion cross section at solar energies are difficult due to the strong Coulomb repulsion between the reactants, the onus falls on theory to provide a robust means for extrapolating from the region where experimental data is available down to the desired astrophysical regime. We present the first microscopic calculations of $^3$He$(\alpha,\gamma)^7$Be with explicit inclusion of three-nucleon forces. Our prediction of the astrophysical $S$ factor qualitatively agrees with experimental data. We further incorporate experimental bound-state and scattering information in our calculation to arrive at a more quantitative description. This process reveals that our current model lacks sufficient repulsion in the $1/2^+$ channel of our model space to simultaneously reproduce elastic-scattering data. This deficit suggests that $^3$He$(\alpha,\gamma)^7$Be probes aspects of the nuclear force that are not currently well-constrained.