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.

Abstract. Most important for the identification of chiral symmetry in atomic nuclei is to establish a pair of bands that are near-degenerate in energy, but also in B(M 1) and B(E2) transition probabilities. Dedicated lifetime measurements were performed for four bands of 194 Tl, including the pair of four-quasiparticle chiral bands with close near-degeneracy, considered as a prime candidate for best chiral symmetry pair. The lifetime measurements confirm the excellent near-degeneracy in this pair and indicate that a third band may be involved in the chiral symmetry scenario.Chiral systems can exist in nuclei with triaxially deformed shape. Such nuclei rotate collectively predominantly around their intermediate axis. Should the valence nucleons have both particle and hole nature, their singleparticle angular momenta would align along the short and long nuclear axes, respectively. Then the total angular momentum of the nucleus will have large projections along the three major nuclear axes, forming a left-handed or a right-handed systems and exhibiting chiral symmetry.Nuclear chiral symmetry generates a pair of rotational bands with the same parity and with near-degenerate properties; for instance they have similar excitation energies, alignments, and reduced B(M 1) and B(E2) transition probabilities [1]. Most of the chiral bands known to date have been identified based on similarity in the excitation energy and alignments, but very often the most crucial chirality test (see ref.[2]), i.e. the similarity in the B(M 1) and B(E2) transition rates remain outstanding, because it needs dedicated lifetime measurements.The formation of more than one chiral system in the same nucleus is a very rare event. To date chiral multiplets were proposed in only two nuclei, Tl [5], including the only fourquasiparticle chiral pair known to date. This is also the only chiral pair for which chirality persists through a backbend. Furthermore, this chiral pair shows perhaps the best near-degeneracy found to date [6].The 181 Ta( 18 O, 5n) reaction was employed at a beam energy of 91 MeV. The target was a 1 mg/cm 2 181 Ta foil with a thick Bi layer evaporated on the back. The recoils were completely stopped in the Bi backing. The emitted γ-rays were detected with the AFRODITE array [7,8] at iThemba LABS, comprising 9 Compton-suppressed clover detectors, and 6 LEPS detectors. The trigger required 3 coincident γ-rays, with at least two detected in the clovers. Four clover detectors were arranged at 45• , another four were placed at 135• , while the remaining detectors were situated at 90• with respect to the beam direction. Data were sorted into two asymmetric matrices, with the γ-ray energies detected at 45• and at 135• , respectively, stored into one axis, while the coincident γ-ray energies registered at any angle were stored into the second axis. Gated, background-subtracted, forward (45 • ) and backward (135 • ) spectra were used to analyze the Doppler

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Low-spin states of 157 Dy have been studied using the JUROGAM II array, following the 155 Gd (α, 2n) reaction at a beam energy of 25 MeV. The level scheme of 157 Dy has been expanded with four new bands. Rotational structures built on the [523]5/2and [402]3/2 + neutron orbitals constitute new additions to the level scheme as do many of the inter-and intra-band transitions. This manuscript also reports the observation of cross I + → (I-1)and I -→ (I-1) + E1 dipole transitions inter-linking structures built on the [523]5/2 -(band 5) and [402]3/2 + (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s = -i related to possible octupole correlations.Two previous experiments conducted with large Ge detector arrays used heavy-ion induced reactions 150 Nd( 12 C,5n) and 124 Sc( 36 S,3n) [71,72,97] to study the medium to high-spin states of 157 Dy. These experiments reported rotational bands built on the h9/2[521]3/2 -, i13/2[651]3/2 + and h11/2[505]11/2neutrons configurations but reported no transitions linking these structures. To this end we have performed in-beam measurements using the JUROGAM II array to study the rotational bands of 157 Dy and to search for evidence of octupole correlations. We report on four new bands as well as many new linking transitions relative to the previously observed structures.The rotational behaviour of the new bands is described in terms of quasi-particle assignments, and the observed alignment properties are analyzed within the framework of the cranked shell model. II. Experimental details and analysisExcited states of 157 Dy were populated using the 155 Gd (α, 2n) reaction at a beam energy of 25 MeV. The 155 Gd target was 0.98 mg/cm 2 thick with a purity of 91%. Gamma-rays following the fusion evaporation reaction were detected with the JUROGAM II multi-detector array [73] in JYFL, Jyväskylä, Finland. The spectrometer setup comprised 39 high-purity germanium detectors, all with BGO escape suppression shields; 15 EUROGAM coaxial detectors (Phase 1 [75] and GASP [74] type) and 24 EUROGAM Phase II clover detectors [76]. Approximately 14 x 10 9 γ-γ events were unfolded from the data in the off-line analysis and replayed into γ-γ Radware [77, 78] coincidence matrices, which were used to construct the level scheme of 157 Dy. The spins and parities for the new rotational structures were successfully assigned using the Directional Correlation from Oriented States (DCO ratios/RDCO) [79, 80] and linear polarization anisotropy (Ap) methods [81]. While Ap is given as used in [82], the DCO matrices were constructed using data from detectors in the rings at 158° and 86°+94°, thus the RDCO for the JUROGAM II array in this work is; RDCO = I γ1(at 158º : gated on γ2 near 90 º) / I γ1(near 90º : gated on γ2 at 158º)

New candidate chiral nucleus in theA ≈ 80 mass region: 82 35 Br 47 C. Liu ( ), S. Y. Wang ( ) , * B. Qi ( ), S. Wang ( ), D. P. Sun ( ), and Z. Q. Li ( )