Detailed Study of the $^{59}$Cu(p,$\alpha)^{56}$Ni Reaction and Constraints on Its Astrophysical Reaction Rate

The $^{59}$Cu$(p,\alpha)^{56}$Ni reaction plays an important role in explosive astrophysical scenarios such as Type I X-ray bursts and the $\nu p$-process in neutrino-driven winds following a core-collapse supernova. In both cases, this reaction has been proposed to significantly affect the synthesis of heavier nuclei by regulating the flow of nucleosynthesis through the Ni--Cu cycle. In this work, we present a direct measurement of the $^{59}\mathrm{Cu}(p,\alpha)^{56}\mathrm{Ni}$ excitation function from 2.43--5.88 MeV in the center-of-mass frame. The experiment was performed in inverse kinematics using the high-efficiency MUSIC active-target detector at FRIB. This measurement allowed tight constraints to be placed on the astrophysical reaction rate. The derived stellar rate is systematically lower than the REACLIB rate and remains below the competing $(p,\gamma)$ rate for $T_9 \lesssim 3$.