We present a new nucleosynthesis process that may take place on neutron-rich ejecta experiencing an intensive neutrino flux. The nucleosynthesis proceeds similarly to the standard $r$ process, a sequence of neutron captures and beta decays with, however, charged-current neutrino absorption reactions on nuclei operating much faster than beta decays. Once neutron-capture reactions freeze out the produced $r$ process, neutron-rich nuclei undergo a fast conversion of neutrons into protons and are pushed even beyond the $\beta$ stability line, producing the neutron-deficient $p$ nuclei. This scenario, which we denote as the $\nu r$ process, provides an alternative channel for the production of $p$ nuclei and the short-lived nucleus ${}^{92}\mathrm{Nb}$. We discuss the necessary conditions posed on the astrophysical site for the $\nu r$ process to be realized in nature. While these conditions are not fulfilled by current neutrino-hydrodynamic models of $r$-process sites, future models, including more complex physics and a larger variety of outflow conditions, may achieve the necessary conditions in some regions of the ejecta.

• Received 18 May 2023
• Revised 29 December 2023
• Accepted 13 March 2024

DOI:https://doi.org/10.1103/PhysRevLett.132.192701

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society