Underground experimental study finds no evidence of low-energy resonance in the Li-6(p, gamma) Be-7 reaction

The astrophysical Li-6(p, gamma) Be-7 reaction occurs during Big Bang nucleosynthesis and the pre-main sequence and main sequence phases of stellar evolution. The low-energy trend of its cross section remains uncertain, since different measurements have provided conflicting results. A recent experiment reported a resonancelike structure at center-of-mass energy 195 keV, associated to a positive-parity state of Be-7. The existence of such resonance is still a matter of debate. We report a new measurement of the Li-6(p, gamma) Be-7 cross section performed at the Laboratory for Underground Nuclear Astrophysics, covering the center-of-mass energy range E = 60-350 keV. Our results rule out the existence of low-energy resonances. The astrophysical S-factor varies smoothly with energy, in agreement with theoretical models.