We present the first missing mass spectrum of the unbound nucleus ${}^{10}\mathrm{He}$, measured at RIKEN using the ${}^{11}\mathrm{Li}\left(d,{}^3\mathrm{He}\right)$ reaction at 50A MeV. ${}^{10}\mathrm{He}$ is believed to be a three-body ${}^8\mathrm{He}+n+n$ resonance beyond the limit of nuclear binding. Our observation of a new decay branch, ${}^6\mathrm{He}+4n$, and of a puzzling reduction of the ${}^{11}\mathrm{Li}\left(d,{}^3\mathrm{He}\right){}^{10}\mathrm{He}$ cross section challenges this view. Moreover, our experiment shows a new trend in the evolution of the proton spectroscopic strength in Li isotopes deduced from the comparison of the $\left(d,{}^3\mathrm{He}\right)$ cross sections on ${}^{7,8,9,11}\mathrm{Li}$ with theoretical predictions. We discuss new questions about physics beyond the limits of nuclear existence raised by these findings.

• Received 11 June 2014
• Revised 9 March 2015
• Corrected 14 October 2015

DOI:https://doi.org/10.1103/PhysRevC.92.041302