Spectroscopy of the $^5$H superheavy hydrogen isotope

The formation of the $^5$H superheavy hydrogen isotope was experimentally sought in the reactions induced by stopped $\pi^-$ mesons absorbed by $^9$Be nuclei. Peaks in missing-mass spectra were observed in two reaction channels, $^9$Be$(\pi^-, pt)X$ and $^9$Be$(\pi^-, dd)X$, and were attributed to the $^5$H resonance states. The lowest state has parameters $Er=5.5\pm0.2\,$MeV and $\Gamma=5.4\pm0.5\,$MeV [$E_r$ is the resonance energy measured from the (triton + two neutrons) threshold]. Therefore, $^5$H is bound more weakly than $^4$H. Excited states of $^5$H were also observed. All three resonance levels ($E_{1r} = 10.6\pm 0.3\,$MeV, $\Gamma _{1r} = 6.8\pm0.5\,$MeV; $E_{2r} = 18.5\pm0.4\,$MeV, $\Gamma _{2r} = 4.8\pm1.3\,$MeV, $E_{3r} = 26.7\pm0.4\,$MeV, $\Gamma _{3r} = 3.6\pm1.3\,$MeV) can decay into five free nucleons.