First sub-MeV nuclear reaction measurements in a heavy-ion storage ring

Heavy-ion storage rings present a novel approach to studying nuclear reactions for astrophysics that have so far resisted traditional methods. In this paper, we report the first nuclear reactions studied in a ring at sub-MeV centre-of-mass energies. This is a major advance in nuclear reaction measurements at rings that lays the foundations for future investigations to address key problems in nuclear astrophysics affecting a wide range of stellar environments. We investigated the $_{}^{15}$ N(p,p) $_{}^{15}$ N and $_{}^{15}$ N(p, $\alpha$ ) $_{}^{12}$ C reactions in inverse kinematics from E = 1.125 MeV/u down to E = 426 keV/u, using the CARME array in the low-energy CRYRING@ESR heavy-ion storage ring, located at the GSI Helmholtz Center for Heavy Ion Research. Our (p,p) scattering results are in excellent agreement with theoretical R matrix predictions. We also report on a (p, $\alpha$ ) measurement at E = 426 keV/u, corresponding to E $_{\text{cm}}^{}$  = 403 keV, by far the lowest energy at which a nuclear reaction has ever been measured in a heavy-ion storage ring.