Phys. Rev. Lett. 124, 022502 (2020) The $^7$H system was populated in the $^2$H($^8$He,$^3$He)$^7$H reaction with
a 26 AMeV $^8$He beam. The $^{7}$H missing mass energy spectrum, the $^{3}$H
energy ...and angular distributions in the $^7$H decay frame were reconstructed.
The $^7$H missing mass spectrum shows a peak which can be interpreted either as
unresolved $5/2^+$ and $3/2^+$ doublet or one of these states at 6.5(5) MeV.
The data also provide indications on the $1/2^+$ ground state of $^7$H located
at 2.0(5) MeV with quite a low population cross section of $\sim 10$ $\mu$b/sr
within angular range $\theta_{\text{cm}} \simeq 6^{\circ} - 30^{\circ}$.
The extremely neutron-rich system \(^{6}\)H was studied in the direct \(^2\text{H}(^8\text{He},{^4\text{He}})^{6}\)H transfer reaction with a \(26 A\) MeV secondary \(^{8}\)He beam. The measured ...missing mass spectrum shows a broad bump at \(\sim 4-8\) MeV above the \(^3\)H+\(3n\) decay threshold. This bump can be interpreted as a broad resonant state in \(^{6}\)H at \(6.8(5)\) MeV. The population cross section of such a presumably \(p\)-wave state (or may be few overlapping states) in the energy range from 4 to 8 MeV is \(d\sigma/d\Omega_{\text{c.m.}} \simeq 190^{+40}_{-80}\) \(\mu\)b/sr in the angular range \(5^{\circ}<\theta_{\text{c.m.}}<16^{\circ}\). The obtained missing mass spectrum is practically free of the \(^{6}\)H events below 3.5 MeV (\(d\sigma/d\Omega_{\text{c.m.}} \lesssim 5\) \(\mu\)b/sr in the same angular range). The steep rise of the \(^{6}\)H missing mass spectrum at \(\sim 3\) MeV allows to derive the lower limit for the possible resonant-state energy in \(^{6}\)H to be \(4.5(3)\) MeV. According to the paring energy estimates, such a \(4.5(3)\) MeV resonance is a realistic candidate for the \(^{6}\)H ground state (g.s.). The obtained results confirm that the decay mechanism of the \(^{7}\)H g.s.\ (located at 2.2 MeV above the \(^{3}\)H+\(4n\) threshold) is the "true" (or simultaneous) \(4n\) emission. The resonance energy profiles and the momentum distributions of fragments of the sequential \(^{6}\)H\( \,\rightarrow \, ^5\)H(g.s.)+\(n\, \rightarrow \, ^3\)H+\(3n\) decay were analyzed by the theoretically-updated direct four-body-decay and sequential-emission mechanisms. The measured momentum distributions of the \(^{3}\)H fragments in the \(^{6}\)H rest frame indicate very strong "dineutron-type" correlations in the \(^{5}\)H ground state decay.
The extremely neutron-rich system \(^{7}\)H was studied in the direct \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H transfer reaction with a 26 AMeV secondary \(^{8}\)He beam Bezbakh et al., Phys. Rev. Lett. 124 ...(2020) 022502. The missing mass spectrum and center-of-mass (c.m.) angular distributions of \(^{7}\)H, as well as the momentum distribution of the \(^{3}\)H fragment in the \(^{7}\)H frame, were constructed. In addition to the investigation reported in Ref. Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502, we carried out another experiment with the same beam but a modified setup, which was cross-checked by the study of the \(^2\)H(\(^{10}\)Be,\(^3\)He\()^{9}\)Li reaction. A solid experimental evidence is provided that two resonant states of \(^{7}\)H are located in its spectrum at 2.2(5) and 5.5(3) MeV relative to the \(^3\)H+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 \(^{7}\)H spectrum. Based on the energy and angular distributions, obtained for the studied \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H reaction, the weakly populated 2.2(5) MeV peak is ascribed to the \(^7\)H ground state. It is highly plausible that the firmly ascertained 5.5(3) MeV state is the \(5/2^+\) member of the \(^7\)H 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 Ref. Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502. Consequently, the two doublet members appeared in the spectrum of \(^{7}\)H in Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502 as a single broad 6.5 MeV peak.
The \(^7\)H system was populated in the \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H reaction with a 26 AMeV \(^8\)He beam. The \(^{7}\)H missing mass energy spectrum, the \(^{3}\)H energy and angular ...distributions in the \(^7\)H decay frame were reconstructed. The \(^7\)H missing mass spectrum shows a peak which can be interpreted either as unresolved \(5/2^+\) and \(3/2^+\) doublet or one of these states at 6.5(5) MeV. The data also provide indications on the \(1/2^+\) ground state of \(^7\)H located at 2.0(5) MeV with quite a low population cross section of \(\sim 10\) \(\mu\)b/sr within angular range \(\theta_{\text{cm}} \simeq 6^{\circ} - 30^{\circ}\).
