Invariant-mass spectrum of $^{11}\mathrm{O}$

Invariant-mass spectrum of ${}^{11}O$

T. B. Webb, R. J. Charity, J. M. Elson, D. E. M. Hoff, C. D. Pruitt, L. G. Sobotka, K. W. Brown, J. Barney, G. Cerizza, J. Estee, W. G. Lynch, J. Manfredi, P. Morfouace, C. Santamaria, S. Sweany, M. B. Tsang, T. Tsang, Y. Zhang, K. Zhu, S. A. Kuvin, D. McNeel, J. Smith, A. H. Wuosmaa, and Z. Chajecki

Phys. Rev. C 101, 044317 – Published 27 April 2020

Abstract

The invariant-mass distribution of ${}^{11}O$ fragments formed in two-neutron-knockout reactions with a ${}^{13}O$ projectile and ${}^{9}{Be}$ target has been further examined. Gating on events where the ${}^{9}C$ decay fragments produced following $2 p$ emission are recoiled transversely in the projectile's frame improves the overall invariant-mass resolution. The observed peak is now shown to have contributions from at least two ${}^{11}O$ levels, in contradiction with the suggestion of Fortune [Phys. Rev. C 99, 051302(R) (2019)]. The data, however, do not differentiate between the ground-state properties obtained by the Gamow coupled-channels calculation and the prompt $2 p$ -decay model of Fortune. The ground-state $2 p$ -decay energy is 4.25(6) MeV in a two-level fit to the data, but lower values are possible if more states contribute to the observed spectrum, as suggested in the previous analysis.