Evidence for Octupole Correlations in Multiple Chiral Doublet Bands

Abstract

Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive-and negative-parity bands have been identified in 78 Br. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei. DOI: 10.1103/PhysRevLett.116.112501 Spontaneous symmetry breaking is a fundamental concept in nature. As a many-body quantum system, the atomic nucleus carries a wealth of information on fundamental symmetries and symmetry breaking. As one example, chiral symmetry breaking in atomic nuclei has attracted considerable attention and intensive discussion since it was first predicted by Frauendorf and Meng [1]. They pointed out that, in the intrinsic frame of the rotating triaxial nucleus, the total angular momentum vector may lie outside the three principal planes, referred to as chiral geometry. The spontaneous chiral symmetry breaking in the laboratory frame may give rise to pairs of nearly degenerate ΔI ¼ 1 bands with the same parity, i.e., chiral doublet bands. Such chiral doublet bands were first observed in N ¼ 75 isotones [2]. So far, more than 30 experimental candidates have been reported in the A ∼ 80, 100, 130, and 190 mass regions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].Based on constrained triaxial covariant density functional theory (CDFT) calculations, it has been suggested that multiple chiral doublet (MχD) bands can exist in a single nucleus [21][22][23][24][25][26]. The theoretical prediction of MχD bands stimulated lots of experimental efforts [27][28][29][30][31]. The first experimental evidence for MχD bands was reported in 133 Ce [27], which confirmed the manifestation of triaxial shape coexistence in this nucleus. Later, Kuti et al. reported a novel type of MχD bands with the same configuration in 103 Rh [29], which showed that chiral geometry can be robust against the increase of the intrinsic excitation energy.Compared to the A ∼ 130 and 100 mass regions, the A ∼ 80 mass region is a relatively new and less studied territory for the investigation of chiral symmetry breaking in rotating nuclei, with only one report of chiral doublet bands based on the πg 9=2 ⊗ νg 9=2 configuration in odd-odd 80 Br [18]. In 78 Br, the πg 9=2 ⊗ νg 9=2 band was suggested to have an obvious triaxial shape [32], which is suitable for the construction of chiral doublet bands.

Ground state properties and potential energy surfaces of 270Hs from multidimensionally-constrained relativistic mean field model

“…The MDC-CDFTs have been applied to the study on fission barriers and PESs of actinide nuclei [37,39], the third minima in PESs of light actinides [67], the non-axial octupole Y 32 correlations in N = 150 isotones [68] and Zr isotopes [41], axial octupole correlations in MχD [69] and Ba isotopes [70] and shapes of hypernuclei [71,72]. Based on the PESs from MDC-CDFTs, the dynamics of spontaneous and induced fissions in actinide nuclei has been studied [73][74][75][76].…”

Chirality of Nd135 reexamined: Evidence for multiple chiral doublet bands

“…Very recently, four-and six-quasiparticle chiral bands have also been observed in even-even nuclei of the A ≈ 130 mass region ( 136 Nd [18] and 138 Nd [19]). In most nuclei only one chiral doublet was observed, but in a limited subset of chiral nuclei two or more chiral doublets were observed ( 78 Br [20], 103 Rh [12], 105 Rh [13], 133 Ce [9], 136 Nd [18], 195 Tl [21], and possibly 107 Ag [22]), exhibiting the exotic phenomenon of multiple chiral doublet bands (MχD) [23][24][25][26][27][28][29][30][31]. In the even-even nucleus 136 Nd, the record of five nearly degenerate band pairs were identified, with properties in agreement with chiral interpretation within the tilted axis cranking constrained density functional theory (TAC-CDFT) framework [18], which were also successfully described in detail as chiral doublets in the framework of the multi-j shell particle rotor model (PRM) [31].…”

Reexamining nuclear chiral geometry from the orientation of the angular momentum

“…[2][3][4][5][6][7][8]. With the prediction [9] and confirmation [10] of multiple chiral doublets (Mχ D) in a single nucleus, the investigation of chirality continues to be one of the hottest topics in nuclear physics [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…In this work, the PRM will be used. The basic microscopic inputs for PRM can be obtained from the constrained covariant density functional theory (CDFT) [9,10,18,20,21,37,56]. PRM is a quantal model consisting of the collective rotation and the intrinsic singleparticle motions, which describes a system in the laboratory reference frame.…”