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

The Li-6(p,gamma)Be-7 reaction is mainly at work in three nucleosynthesis scenarios: Big Bang Nucleosynthesis, Li-6 depletion in pre-main and in main sequence stars and cosmic ray interaction with interstellar matter. The Li-6(p,gamma)Be-7 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 similar to 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 Li-6(p,gamma)Be-7 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 Li-6(p,gamma)Be-7 S-factor and it is supported by a recent theoretical study.