The interplay of single-particle and collective motions in the low-lying states of ^(21)_(A)Ne with quadrupole-octupole correlations

The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the configurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordinate method based on a covariant den-sity functional theory.The method is demonstrated in the application to the low-lying states of 21ΛNe,where the configurations with theΛhyperon occupying the first(Λ_(s))and second(Λ_(p))lowest-energy states are considered.The results indicate that the positive-parity states are dominated by theα+^(12)C+α+Λ_(s) structure.In contrast,the low-lying negative-parity states are domi-nated by a strong admixture ofα+16O+Λ_(s) structure andα+12C+α+Λ_(p) structure due to the inclusion of octupole correlations.As a result,the low-lying negative-parity states become much lower than what is expected from the previous studies without the mixing,and the electric multipole transition strengths are significantly quenched.

Configuration mixing in low-lying spectra of carbon hypernuclei

The spectroscopy of hypernuclear low-lying states is very important to understand the structure of hypernuclei and the hyperon impurity effect in atomic nuclei. Several novel phenomena about A hyperon have already been discovered by studying energy spectra and electromagnetic transitions of low-lying states in p-shell hypernuclei. One of them is the shrinkage effect of A hyperon in 6Li,

Beyond mean-field approach for pear-shaped hypernuclei

We develop both relativistic mean field and beyond approaches for hypernuclei with possible quadrupole-octupole deformation or pear-like shapes based on relativistic point-coupling energy density functionals. The symmetries broken in the mean-field states are recovered with parity, particle-number and angular momentum projections. We take_Λ^(21)Ne as an example to illustrate the method, where the Λ hyperon is put on one of the two lowest-energy orbits(labeled as Λ_s, Λ_p), respectively. We find that the Λ hyperon in both cases disfavors the formation of a reflection-asymmetric molecular-like^(16)O+α structure in^(20)Ne, which is consistent with the Nilsson diagram for the hyperon in(β_2, β_3) deformation plane. In particular, we show that the negative-parity states with the configuration^(20)Ne(K~π= 0^-)  Λ_s are close in energy to those with the configuration^(20)Ne(K~π= 0^+)Λ_p, even though they have very different structures. The Λ_s(Λ_p) becomes more and more concentrated around the bottom(top) of the"pear" with the increase of octupole deformation.

Advances in modeling nuclear matrix elements of neutrinoless double beta decay

The neutrinoless double beta(0vββ)decay is a hypothetical weak process which manifests itself in the“low-energy”environment of atomic nuclei as two neutrons in a parent nucleus(A,Z)decays into two protons in a daughter nucleus(A,Z+2)with the emission of two electrons but no(anti)neutrinos[1].