Speaker
Description
The cosmological lithium problem has been known as the outstanding discrepancy of primordial lithium abundances between observations and theoretical predictions. We have measured key nuclear reactions which act to reduce $^7$Li during the big bang nucleosynthesis (BBN), namely, $^7$Be$(n,p)^7$Li and $^7$Be$(n,α)^4$He, by means of the Trojan Horse method [1].
We also performed $R$-matrix fits to data sets including both the previous and present cross sections of the $(n,p_0)$, $(n,p_1)$ and $(n,\alpha)$ reaction channels based on the resonances at known excited levels. This analysis resulted in an improved uncertainty evaluation of the $(n,p_0)$ cross section, and the first-ever quantification of the $(n,p_1)$ contribution in the BBN energy region.
We implemented the revised total reaction rate summing both the $(n,p_0)$ and $(n,p_1)$ contributions in one of the state-of-the-art BBN codes PRIMAT. It results in a reduction of the predicted $^7$Li abundance by about one tenth, which would offer less nuclear physics uncertainty to further theoretical works on the cosmological lithium problem.
[1] S. Hayakawa et al., Astrophys. J. Lett., 915, (2021), L13.
