Experimental Challenge to the Cosmological Li Problem

The cosmological Li problem, the overproduction of⁷Li in the big bang nucleosynthesis (BBN), still is one of the serious remaining problems for the big bang model. Several experiments were performed for the problem in recent years, especially, on the reaction channel of⁷Be+n. These efforts were summarized including our works by indirect methods. The⁷Be(n,α)⁴He reaction was found to have a major component of the p-wave contribution, not s-wave as thought previously. The contribution of this reaction for destruction of⁷Be can be concluded to be less effective than assumed before, and thus this reaction does not help to solve the Li problem. A new measurement of the⁷Be(n,p)⁷Li reaction was reported to be larger than before at low energies, and the⁷Be(n,p₁)⁷Li* reaction is also shown to be significant for the Li problem by our new study at JAEA, suggesting a need of further work on this reaction for the Li problem. Other possibilities for⁷Be destruction was also discussed, especially by the⁷Be+d channel.