LUNA measurement found no evidence of a low-energy resonance in 6Li(p, γ)7Be reaction

Abstract

The ⁶Li(p, γ)⁷Be reaction is mainly at work in three nucleosynthesis scenarios: Big Bang Nucleosynthesis, ⁶Li depletion in pre-main and in main sequence stars and cosmic ray interaction with interstellar matter. The ⁶Li(p, γ)⁷Be S-factor trend was poorly constrained at astrophysical energies because of conflicting experimental results reported in literature. A recent direct measurement, indeed, found a resonance-like structure at E_c.m. = 195 keV, corresponding to an excited state at E_x ∼ 5800 keV in ⁷Be which, however, has not been confirmed by either other direct measurements or predicted by theoretical calculations.

In order to clarify the existence of this resonance, a new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), located deep underground in Gran Sasso Laboratory. Thanks to the extremely low background environment, the ⁶Li(p, γ)⁷Be cross section was measured in the center-of-mass energy range E = 60-350 keV with unprecedented sensitivity.

No evidence for the alleged resonance was found. LUNA results was confirmed by latest published indirect determination of ⁶Li(p, γ)⁷Be S-factor and it is supported by a recent theoretical study.