Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei

The structure of levels of superheavy hydrogen isotopes ^4–6H is analyzed on the basis of a record statistics of experimental data on the absorption of negatively charged pions by light nuclei. Qualitatively new experimental data are obtained for the spectroscopy of the superheavy hydrogen isotopes ⁵H and ⁶H. Peaks due to four resonance states of ⁵H are observed in the missing-mass spectra for the reaction channels ⁹Be(π ^?, pt)X and ⁹Be(π^?, dd)X. A structure that is associated with four resonance states of ⁶H is observed in the missing-mass spectra for the reaction channels ⁹Be(π^?, pd)X and ¹¹B(π^?, p ⁴He)X. On the basis of the results presented for ground-state parameters, it can be concluded that the binding energy of superheavy hydrogen isotopes decreases as the number of neutrons increases. Excited levels of the isotopes ⁵H and ⁶H are observed for the first time. On the energy scale, all of these states lie above the threshold for decay to free nucleons.