Neutrino-Induced Nucleosynthesis of $A>64$ Nuclei: The $\nu p$ Process

We present a new nucleosynthesis process that we denote as the $\nu p$ process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers $A>64$, making this process a possible candidate to explain the origin of the solar abundances of ${}^{92,94}\mathrm{Mo}$ and ${}^{96,98}\mathrm{Ru}$. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star.

Figure 1

Evolution of the abundances of neutrons, protons, alpha particles, and ${}^{56}\mathrm{Ni}$ in a nucleosynthesis trajectory resulting from model B07 of Ref. 24. The abundance, $Y$, is defined as the number of nuclei of the species $i$ present divided by the total number of nucleons which is conserved during the calculation. The solid (dashed) lines display the nucleosynthesis results which include (omit) neutrino and antineutrino absorption interactions after nuclei are formed. The abscissa measures the time since the onset of the supernova explosion.

Figure 2

The panel shows the isotopic abundances for model B07 of Ref. 24 relative to solar abundances [29]. The solid circles represent calculations where (anti)neutrino-absorption reactions are included in the nucleosynthesis while for the open circles neutrino interactions are neglected.

Figure 3

Light $p$-nuclei abundances in comparison to solar abundances as a function of $Y_e$. The $Y_e$ values given are the ones obtained at a temperature of 3 GK that corresponds to the moment when nuclei are just formed and the $\nu p$ process starts to act.