Impact of Light-mass Nuclear Reactions on the r -process Nucleosynthesis, Revisited

Light-mass nuclear reactions can play a significant role in r -process nucleosynthesis in core-collapse supernovae (SNe) and collapsars. We investigate the sensitivity of both weak and main r -process nucleosyntheses, which are responsible for the production of the first and second plus third r -process peak nuclei, respectively, to the light-mass nuclear reactions up to oxygen isotopes. We extend the reaction network to include more neutron-rich isotopes and update reaction rates using recent experimental results. For the explosion mechanisms, the sensitivity studies have previously been done in ν -driven wind SNe assuming relatively high initial neutron-to-proton ratio with high entropy. We here consider magnetohydrodynamic jet SNe and collapsars in addition to the ν -driven winds. We use a simple exponential decay model for slowly expanding disk outflows, which manifest themselves in various disk winds from collapsars, magnetohydrodynamic jets, binary neutron star mergers, as well as ν -driven winds. We study the competition between the dynamical expansion timescale of the system and the collision timescales for various nuclear reactions and β- decays in order to identify the main reaction flow paths. We find the sensitivities of the main r -process to 14 C( n , γ ) 15 C, 18 O( n , γ ) 19 O, and 8 Li( α , n ) 11 B, which are as large as 16%, 24%, and 0.6%, respectively, for the magenetohydrodynamic jet SN environment, and for the weak r -process to ( n , γ ) and ( α , n ) reactions, which depend on different astrophysical sites.