Resonant states in 7H: Experimental studies of the 2H(8He,3He) reaction

The extremely neutron-rich system ⁷H was studied in the direct ²H(⁸He,³He)⁷H transfer reaction with a 26 A MeV secondary ⁸He beam [Bezbakh et al., Phys. Rev. Lett. 124, 022502 (2020), 10.1103/PhysRevLett.124.022502]. The missing mass spectrum and center-of-mass angular distributions of ⁷H, as well as the momentum distribution of the ³H fragment in the ⁷H frame, were constructed. In addition, we carried out another experiment with the same beam but a modified setup, which was cross-checked by the study of the ²H(¹⁰Be,³He)⁹Li reaction. A solid experimental evidence is provided that two resonant states of ⁷H are located in its spectrum at 2.2(5) and 5.5 (3 )MeV relative to the ³H+4 n decay threshold. Also, there are indications that the resonant states at 7.5(3) and 11.0 (3 )MeV are present in the measured ⁷H spectrum. Based on the energy and angular distributions, obtained for the studied ²H(⁸He,³He)⁷H reaction, the weakly populated 2.2(5)-MeV peak is ascribed to the ⁷H ground state. It is highly plausible that the firmly ascertained 5.5(3)-MeV state is the 5 /2⁺ member of the ⁷H excitation 5 /2⁺-3 /2⁺ doublet, built on the 2⁺ configuration of valence neutrons. The supposed 7.5-MeV state can be another member of this doublet, which could not be resolved in Bezbakh et al. [Phys. Rev. Lett. 124, 022502 (2020), 10.1103/PhysRevLett.124.022502]. Consequently, the two doublet members appeared in the spectrum of ⁷H in the work mentioned above as a single broad 6.5-MeV peak.