Neutrino-Induced Nucleosynthesis in Helium Shells of Early Core-Collapse Supernovae

Abstract

We summarize our studies on neutrino-driven nucleosynthesis in He shells of early core-collapse supernovae with metallicities of $Z\lesssim 10^{-3}{Z}_{\odot }$. We find that for progenitors of $\sim 11$--$15{\mathrm{M}}_{\odot }$, the neutrons released by ${}^4\mathrm{He}(\bar{\hat{I}}{½}_e,e^{+}n{)}^3\mathrm{H}$ in He shells can be captured to produce nuclei with mass numbers up to $A\sim 200$. This mechanism is sensitive to neutrino emission spectra and flavor oscillations. In addition, we find two new primary mechanisms for neutrino-induced production of ${}^9$Be in He shells. The first mechanism produces ${}^9$Be via ${}^7\mathrm{Li}(n,{\hat{I}}^3{)}^8\mathrm{Li}(n,{\hat{I}}^3{)}^9\mathrm{Li}(e^{-}\bar{\hat{I}}{½}_e{)}^9\mathrm{Be}$ and relies on a low explosion energy for its survival. The second mechanism operates in progenitors of $\sim 8{\mathrm{M}}_{\odot }$, where ${}^9$Be can be produced directly via ${}^7\mathrm{Li}{(}^3\mathrm{H},n_0{)}^9\mathrm{Be}$ during the rapid expansion of the shocked He-shell material. The light nuclei ${}^7$Li and ${}^3$H involved in these mechanisms are produced by neutrino interactions with ${}^4$He. We discuss the implications of neutrino-induced nucleosynthesis in He shells for interpreting the elemental abundances in metal-poor stars.

6 pages, 3figures, OMEG 2015 conference proceedings, to appear in EPJ WOC proceedings