First direct measurement of Cu59(p,α)Ni56: A step towards constraining the Ni-Cu cycle in the cosmos

Reactions on proton-rich nuclides drive the nucleosynthesis in core collapse supernovae (CCSNe) and in x-ray bursts (XRBs). CCSNe eject the nucleosynthesis products to the interstellar medium and hence are a potential inventory of p nuclei, whereas in XRBs nucleosynthesis powers the light curves. In both astrophysical sites the Ni-Cu cycle, which features a competition between Cu59(p,α)Ni56 and Cu59(p,γ)Zn60, could potentially halt the production of heavier elements. Here, we report the first direct measurement of Cu59(p,α)Ni56 using a reaccelerated Cu59 beam and a cryogenic solid hydrogen target. Our results show that the reaction proceeds predominantly to the ground state of Ni56, and the experimental rate has been found to be lower than Hauser-Feshbach based statistical model predictions. New results hints that the νp process could operate at higher temperatures than previously inferred and therefore remains a viable site for synthesizing the heavier elements.