Shape Coexistence Of Odd-A Ne Isotopes And The Impurity Effects Of Λ Hyperon

With the new generation of radioactive beam facilities and detectors upgraded,most of the nuclei are found deformed with many interesting phenomena,such as the shape coexistence.The hypernuclear systems have become one of the significant branches of nuclear physics due to the strangness degree of freedom.In recent years,neon isotopes have attracted great attentions theoretically and experimentally.The multidimensionally constrained relativistic mean-field(MDC-RMF)theory has considered effectively the multipole deformations βλμ and has achieved great successes in the studies of deformed nuclei and hypernuclei.In this work,the possible shape coexistence in the odd-A neon isotopes 19-33 Ne and the impurity effects of single-Λ hyperon occupying the lowest s(1/2+[000])and three p(1/2-[110],1/2-[101],3/2-[101])orbitals have been studied,base on MDC-RMF model,with the PK1 parameter set for the NN interaction and the PK1-Y1 for the ΛN interaction.The blocking effect has been included in the framework of BCS approach to deal with the pairing.The details are as follows:(1)By blocking the unpaired odd neutron in different orbitals around the Fermi surface,the nuclear ground state as well as the local energy minima are determined.By examining the potential energy curves(PECs),possible shape coexistences in 27,29Ne and a possible triple shape coexistence in 31Ne are predicted.Regarding 27Ne,with the odd neutron blocked in 1/2+[200]and 3/2+[202]orbitals,the ground state in a prolate shape at the deformation of β2=0.190 and the second energy minimum exhibiting an oblate shape at β2=-0.130 are observed,respectively.A small energy difference of 0.333 MeV and a barrier with a height of 0.984 MeV between them are observed,supporting the possible shape coexistence in 27Ne.Similarly,in 29Ne,with the odd neutron blocked in 3/2+[202],the prolate ground state is identified at β2=0.080 while the configuration with odd neutron occupying 1/2+[200]leads to the oblate second local minimum at β2=-0.075.In the case of 31Ne,a possible triple shape coexistence,including the ground state at β2=0.191 with the odd neutron blocked at 1/2-[321],the second local energy minimum at oblate deformation β2=-0.090 with the odd neutron at 7/2-[303],and the third local minimum at prolate deformation β2=0.429 with the odd neutron at 3/2+[202],is predicated.(2)To explore the impurity effects of sΛ and pΛ hyperons,the nuclear quadrupole deformations,r.m.s.radii,binding energies,and the density distributions are compared in detail for Ne isotopes and the corresponding hypernuclei with the single Λ occupying the lowest s(1/2+[000])and three p(1/2-[110],1/2-[101],3/2-[101])orbitals.The sΛhyperon shows obvious shrinkage effects,which reduces the nuclear size and deformation.In contrast,a pΛ hyperon shows strong polarization effects which may enhance the nuclear deformation.Meanwhile,the pΛ hyperon occupying different orbitals has different effects:the hyperon from the 1/2-[110]orbital drives the shape of the nuclei to be more prolate;and the hyperon on the 3/2-[101]or 1/2-[101]state makes the nuclear shape more oblate.Besides,with the addition of the sΛ hyperon,the energy difference ΔE between the ground state and the second local energy minimum is reduced,which may increase the probabilities of shape coexistence.However,in the case of introducing a pΛ hyperon,it is at a distinct disadvantage for the shape coexistence in most of hypernuclei.