New Thermonuclear Rate of 7Li(d,n)24He relevant to the Cosmological Lithium Problem

TL;DR

This study reevaluates the 7Li(d,n)24He reaction rate using recent experimental data, significantly reducing previous estimates and assessing its impact on primordial element abundances, ultimately confirming the persistence of the cosmological lithium problem.

Contribution

The paper provides the first experimentally constrained uncertainties for the 7Li(d,n)24He reaction rate and incorporates the subthreshold resonance, refining the rate used in Big Bang Nucleosynthesis models.

Findings

The new reaction rate is about 60 times smaller than previous estimates at BBN temperatures.

Updated rates have minimal impact on light element abundances in uniform density models.

In nonuniform models, 7Li production can increase by 10%, and heavier nuclide production by 40%.

Abstract

Accurate 7Li(d,n)24He thermonuclear reaction rates are crucial for precise prediction of the primordial abundances of Lithium and Beryllium and to probe the mysteries beyond fundamental physics and the standard cosmological model. However, uncertainties still exist in current reaction rates of 7Li(d,n)24He widely used in Big Bang Nucleosynthesis (BBN) simulations. In this work, we reevaluate the 7Li(d,n)24He reaction rate using the latest data on the three near-threshold 9Be excited states from experimental measurements. We present for the first time uncertainties that are directly constrained by experiments. Additionally, we take into account for the first time the contribution from the subthreshold resonance at 16.671 MeV of 9Be. We obtain a 7Li(d,n)24He rate that is overall smaller than the previous estimation by about a factor of 60 at the typical temperature of the onset of primordial nucleosynthesis. We implemented our new rate in BBN nucleosynthesis calculations, and we show that the new rates have a very limited impact on the final light element abundances in uniform density models. Typical abundance variations are in the order of 0.002%. For nonuniform density BBN models, the predicted 7Li production can be increased by 10% and the primordial production of light nuclides with mass number A>7 can be increased by about 40%. Our results confirm that the cosmological lithium problem remains a long-standing unresolved puzzle from the standpoint of nuclear physics.