A particle rotor model is developed which couples several valence protons and neutrons to a rigid triaxial rotor core. It is applied to investigating the chirality in odd-A nucleus 135 Nd with πh 2 11/2 ⊗ νh −1 11/2 configuration for the first time in a fully quantal approach. For the two chiral sister bands, the observed energies and the B(M1) and B(E2) values for the in-band as well as interband transitions are reproduced excellently. Root mean square values of the angular momentum components and their probability distributions are used for discussing in detail the chiral geometry of the aplanar rotation and its evolution with angular momentum. Chirality is found to change from a soft chiral vibration to nearly static chirality at spin I = 39/2 and back to another type of chiral vibration at higher spin.Key words: chirality, particle rotor model, aplanar rotation, 135 Nd PACS: 21.60. Ev, 21.10.Re, 23.20.Lv Spontaneous chiral symmetry breaking is a phenomenon of general interest in chemistry, biology and particle physics. Since the pioneering work of nuclear chirality in 1997 [1], much effort has been devoted to further explore this interesting phenomenon. Following the observation of chiral doublet * Corresponding authorEmail addresses: sqzhang@pku.edu.cn (S.Q. Zhang), mengj@pku.edu.cn (J. Meng ) Letter B April 9, 2018 bands in N = 75 isotones [2], more candidates have been reported over more than 20 nuclei experimentally in A∼ 100, 130 and 190 mass regions including odd-odd, odd-A and even-even nuclei [3,4,5,6,7,8,9,10,11,12,13,14]. Chiral symmetry breaking was initially suggested to occur in a stable triaxial deformed nucleus, with a high-j particle-like valence proton (neutron) and a high-j hole-like valence neutron (proton) [1]. In this case, the angular momenta of the core, the valence proton and neutron are mutually perpendicular, arranging in the body-fixed frame into two systems with opposite chirality (left-and right-handed). Due to the restoration of chiral symmetry by quantum tunneling, a pair of near degenerate ∆I = 1 bands -the chiral sister or doublet bands-are observed [1,15]. Preprint submitted to PhysicsTheory wise, chiral doublet bands were first investigated in the oneparticle-one-hole-rotor model (PRM) and the corresponding tilted axis cranking (TAC) approximation [1]. Later on realistic TAC approaches, as the Strutinsky shell correction method with a hybrid Woods-Saxon and Nilsson potential [16], the Skyrme Hartree-Fock model [17], as well as the relativistic mean field model [18,19] has been developed to investigate this new phenomena. Within the TAC mean field approximation, the left-handed and right-handed solutions are exactly degenerate. It is not possible to calculate the energy difference between the bands, which is the consequence of quantum tunneling between the two solutions. Before the onset of chirality of the mean field, the precursor of the symmetry breaking occurs as a soft vibration between the right-and left-handed configurations. These chiral vibrations h...

A particle rotor model (PRM) with a quasi-proton and a quasi-neutron coupled with a triaxial rotor is developed and applied to study chiral doublet bands with configurations of a h 11/2 proton and a h 11/2 quasi-neutron. With pairing treated by the BCS approximation, the present quasiparticle PRM is aimed at simulating one proton and many neutron holes coupled with a triaxial rotor. After a detailed analysis of the angular momentum orientations, energy separation between the partner bands, and behavior of electromagnetic transitions, for the first time we find aplanar rotation or equivalently chiral geometry beyond the usual one proton and one neutron hole coupled with a triaxial rotor.

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Two pairs of nearly degenerate doublet bands in 107 Ag are studied via the relativistic mean-field (RMF) theory and the multiparticle plus rotor model (PRM), which suggests these bands as two distinct sets of chiral doublet bands. For the suggested πg −1 9/2 ⊗ νh 2 11/2 and πg −1 9/2 ⊗ νh 11/2 d 5/2 configurations, the favorable triaxial deformation γ for nuclear chirality can be obtained from the configuration-fixed constrained triaxial RMF calculations. Adopting the PRM, the data available are reproduced very well for the two pairs of doublet bands. Chiral geometry is further conformed by analyzing the angular momentum components. We suggest that two pairs of doublet bands in 107 Ag would be another example of multiple chiral doublet bands.