Relativistic Mean-Field and Beyond Approaches for Deformed Hypernuclei

We report the recent progress in relativistic mean-field (RMF) and beyond approaches for the low-energy structure of deformed hypernuclei. We show that the $\Lambda$ hyperon with orbital angular momentum $\ell=0$ (or $\ell>1$) generally reduces (enhances) nuclear quadrupole collectivity. The beyond mean-field studies of hypernuclear low-lying states demonstrate that there is generally a large configuration mixing between the two components $[^{A-1}Z (I^+) \otimes \Lambda p_{1/2}]^J$ and $[^{A-1}Z (I\pm2 ^+) \otimes \Lambda p_{3/2}]^J$ in the hypernuclear $1/2^-_1, 3/2^-_1$ states. The mixing weight increases as the collective correlation of nuclear core becomes stronger. Finally, we show how the energies of hypernuclear low-lying states are sensitive to parameters in the effective $N \Lambda$ interaction, the uncertainty of which has a large impact on the predicted maximal mass of neutron stars.Comment: 12 pages, 7 figures. A plenary talk given at the 13th International Conference on Hypernuclear and Strange Particle Physics, June 24-29, 2018, Portsmouth, V

Disappearance of nuclear deformation in hypernuclei: a perspective from a beyond-mean-field study

The previous mean-field calculation [Myaing Thi Win and K. Hagino, Phys. Rev. C{\bf 78}, 054311 (2008)] has shown that the oblate deformation in $^{28,30,32}$Si disappears when a $\Lambda$ particle is added to these nuclei. We here investigate this phenomenon by taking into account the effects beyond the mean-field approximation. To this end, we employ the microscopic particle-rotor model based on the covariant density functional theory. We show that the deformation of $^{30}$Si does not completely disappear, even though it is somewhat reduced, after a $\Lambda$ particle is added if the beyond-mean-field effect is taken into account. We also discuss the impurity effect of $\Lambda$ particle on the electric quadrupole transition, and show that an addition of a $\Lambda$ particle leads to a reduction in the $B(E2)$ value, as a consequence of the reduction in the deformation parameter.Comment: 6 pages, 5 figures. The version to appear in Phys. Rev.

Visualizing quantum coherence and decoherence in nuclear reactions

Differential cross sections of nuclear reactions often exhibit characteristic oscillations in the angular distribution originated from an interference of two indistinguishable processes. Here we propose a novel method to visualize origins of such oscillations. This is achieved by taking Fourier transform of scattering amplitudes, following the idea in wave optics. We apply this method to elastic scattering of ¹⁶O+¹⁶O and ¹⁸O+¹⁸O at energies above the Coulomb barrier. The former system shows strong oscillations in the angular distribution due to the nearside-farside interferences, while the oscillations are largely suppressed in the latter system due to a stronger absorption. We show that the images of the former and the latter systems correspond to a double-slit and a single-slit problems in quantum mechanics, respectively