Theoretical Research On The Candidate Chiral Doublet Bands In ¹²⁰I

Chirality is a common phenomenon in nature.The nucleus is a finite quantum multibody system composed of protons and neutrons,in which will also exist the chirality.Based on the particle rotor model（PRM）and the tilted axis cranking（TAC）model,Frauendorf and Meng predicted the existence of chirality in 1997,which has attracted great attention.For a triaxial nucleus,the mutually perpendicular angular momentum of the valence pro-ton,the valence neutron and the core,which alignment along the three principle axis,can be arranged to form two systems with opposite chirality,namely left-and right-handedness.In the laboratory reference frame,with the restoration of chiral symmetry due to quantum tunneling,the so-called chiral doublet bands,i.e.a pair of?I=1 bands（normally regarded as near degen-erate）with the same parity,are observed in triaxial nuclei.In experiment,great achievements have been obtained in observing the chiral doublet bands.More than 30 candidate chiral nucle-us have been reported in A～80,100,130,190 mass region.In addition,based on constrained triaxial covariant density functional theory（CDFT）,Meng et.al.,predicted the existence of multiple chiral doublet（MχD）in 2006.later on,the multiple chiral doublet（MχD）bands have been observed in⁷⁸Br,^103,105Rh,¹⁰⁷Ag and¹³³Ce in experiment.Theoretically,many approaches have been developed to investigate nuclear chirality,such as the particle rotor model（PRM）,the tilted axis cranking model（TAC）,the tilted axis cranking plus random phase approximation（TAC+RPA）,the interacting boson fermion-fermion mod-el（IBFFM）,the pair truncated shell model（PTSM）,and the projected shell model（PSM）.The particle-rotor model（PRM）has been extensively used in the investigation of the chiral rotation due to the advantages of the good angular momentum and simple picture.Compared with the conventional cranking approach,PRM is a quantum mechanical method that describes the sys-tem in the laboratory framework and yields directly the energy splitting and tunneling between doublet bands.In present work,the energy splitting and the in-band B（M1）/B（E2）values of chiral doublet bands in odd-odd nucleus have been systematic studied.Based on the reported positive-parity doublet bands in¹²⁰I,the rotational alignment and B（M1）/B（E2）ratios have been extracted,and the corresponding configuration of the doublet bands is assigned asπh_11/2?νh^-1_11/2.The tri-axial RMF theory and the self-consistent TAC-RMF theory have been performed to investigate triaxial deformation withπh_11/2?νh^-1_11/2configuration of¹²⁰I.The suitable triaxial deformation has supported the existence of chiral doublet bands in¹²⁰I.Based on the assignedπh_11/2?νh^-1_11/2configuration,the doublet bands in 120I have been studied in two quasiparticles coupled with a triaxial rotor model.The calculated energy spectra,energy staggering parameter S（I）,and the intraband B（M1）/B（E2）are in good agreement with the available experimental data.In addi-tion,the calculated effective angles between the angular momenta of the core,valence proton and neutron also indicates a obvious chiral geometry of aplanar rotation.Thus we suggest the reported positive-parity doublet bands in¹²⁰I as chiral doublet bands.