High-energy break-up of 6Li as a tool to study the Big-Bang nucleosynthesis reaction 2H(alpha,gamma)6Li

TL;DR

This study measures the 2H(alpha,gamma)6Li reaction cross section via 6Li break-up at high energy to refine Big-Bang nucleosynthesis predictions of 6Li abundance, revealing lower primordial levels than previous estimates.

Contribution

It provides a new experimental approach to determine the 2H(alpha,gamma)6Li cross section at low energies, confirming theoretical models of Coulomb-nuclear interference.

Findings

Evidence of Coulomb-nuclear interference in 6Li break-up

Lower upper limits for primordial 6Li abundance

Drop of the S_24-factor at low energies

Abstract

The recently claimed observations of non-negligible amounts of 6Li in old halo stars have renewed interest in the Big-Bang Nucleosynthesis (BBN) of 6Li. One important ingredient in the predicted BBN abundance of 6Li is the low-energy 2H(alpha,gamma)6Li cross section. Up to now, the only available experimental result for this cross section showed an almost constant astrophysical S-factor below 400 keV, contrary to theoretical expectations. We report on a new measurement of the 2H(alpha,gamma)6Li reaction using the break-up of 6Li at 150 A MeV. Even though we cannot separate experimentally the Coulomb contribution from the nuclear one, we find clear evidence for Coulomb-nuclear interference by analyzing the scattering-angular distributions. This is in-line with our theoretical description which indicates a drop of the S_24-factor at low energies as predicted also by most other models. Consequently, we find even lower upper limits for the calculated primordial 6Li abundance than before.