Two-Proton Emission from the Ground State ofO12

Abstract

The three-body decay ${}_{}{}^{12}{}_{}{}^{}\mathrm{O}\to 2p+{}_{}{}^{10}{}_{}{}^{}\mathrm{C}$ was studied following production via single-neutron stripping from a radioactive ${}_{}{}^{13}{}_{}{}^{}\mathrm{O}$ projectile. This is the first observation of two-proton emission from an unbound ground state where the one-proton emission channel is energetically closed beyond the lightest case of ${}_{}{}^6{}_{}{}^{}\mathrm{Be}$. No evidence for ${}_{}{}^2{}_{}{}^{}\mathrm{He}$ emission is seen, despite predictions for a large diproton branching ratio. An upper limit of 7% (95% C.L.) is established for this decay branch. The implications of the small diproton branching ratio observed here and seen previously in ${}_{}{}^6{}_{}{}^{}\mathrm{Be}$ are discussed.