Resonance excitations in $^7$Be(d,p)$^8$Be$^\ast$ to address the cosmological lithium problem

TL;DR

This study measured resonance excitations in the $^7$Be(d,p)$^8$Be* reaction at CERN to evaluate their impact on primordial lithium abundance, finding increased reaction rates but still insufficient to resolve the lithium problem.

Contribution

First experimental measurement of excited states up to 22 MeV in $^8$Be for this reaction, providing new data to assess resonance effects on Big Bang nucleosynthesis.

Findings

Inclusion of the 16.63 MeV state increases the S-factor to 167 MeV b.

Resonance contributions are significant but do not fully resolve the lithium discrepancy.

The reaction rate remains insufficient to explain the primordial lithium abundance anomaly.

Abstract

The anomaly in lithium abundance is a well-known unresolved problem in nuclear astrophysics. A recent revisit to the problem tried the avenue of resonance enhancement to account for the primordial $^7$Li abundance in standard big-bang nucleosynthesis (BBN). Prior measurements of the $^7$Be(d,p)$^8$Be* reaction could not account for the individual contributions of the different excited states involved, particularly at higher energies close to the Q-value of the reaction. We carried out an experiment at HIE-ISOLDE, CERN to study this reaction at E$_{cm}$ = 7.8 MeV, populating excitations up to 22 MeV in $^8$Be for the first time. The angular distributions of the several excited states have been measured and the contributions of the higher excited states in the total cross section at the relevant big-bang energies were obtained by extrapolation to the Gamow window using the TALYS code. The results show that by including the contribution of the 16.63 MeV state, the maximum value of the total S-factor inside the Gamow window comes out to be 167 MeV b as compared to earlier estimate of 100 MeV b. However, this still does not account for the lithium discrepancy.