Département de Physique Nucléaire

Recently, in hypernuclear physics, we had three neutron-rich Λ hypernuclei, nnΛ, ⁶_ΛH and ⁷_ΛHe. These observations are very important by following reason: one of the research goals in hypernuclear physics is to study new dynamical features by injecting a Λ particle into a nucleus. Since there is no Pauli principle between nucleons and a Λ particle, the Λ participation gives rise to more bound states and significant contraction of nuclear cores, especially in light systems. If a Λ particle is added to neutron-rich nuclei to have a weakly bound state or resonant one, a resultant hypernucleus will become more stable against neutron decay. Three observed hypernuclei are such systems. Currently, it is important to investigate structure of these Λ hypernuclei theoretically. For this purpose, I will report these hypernuclei within the framework of nnΛ, tnnΛ and αΛNN three- and four-body models.

The following will be reported together with my calculation method:

(1) To study nnΛ system, the coupled channel calculation of NNΛ and NNΣ is performed. We do not find any nnΛ bound state, which is inconsistent with the interpretation of the data.

(2) Interactions among the constituent subunits in ⁶_ΛH are determined so as to reproduce reasonably well the observed low energy properties of the tn, tΛ and tnn. As long as we reproduce the energy and width of ⁵H within the error bar, the ground state of ⁶_ΛH is obtained as a resonant state.

(3) In our previous work, we predicted the ground state, 1/2+ and the excited states, 3/2⁺₁ and 5/2⁺. The recent observed data at Jlab are in good agreement with our prediction. Here, I will report another new states, 3/2⁺₂ and 5/2⁺₂ in ⁷_ΛHe which is second 2⁺ state of ⁶He coupled to 0s-orbit of Λ particle. I will report also the structure of these spectra.

References:

Resonant states of the neutron-rich hypernucleus ⁷_ΛHe,
E. Hiyama, M. Isaka M. Kamimura, T. Myo, T. Motoba, Phys. Rev. C 91, 054316 (2015).

Four-body structure of neutron-rich hypernucleus ⁶_ΛH,
E. Hiyama, S. Ohnishi, M. Kamimura, Y. Yamamoto, Nucl. Phys. A908, 29 (2013).

This seminar is organized within the framework of the ESNT http://esnt.cea.fr for the project entitled "Computation of three- and four-neutron resonances... ", 24^thOct.-1^stNov., http://esnt.cea.fr/Phocea/Page/index.php?id=55