${}^{128}\mathrm{Cs}$ as the Best Example Revealing Chiral Symmetry Breaking

The results of the Doppler-shift attenuation method lifetime measurements in partner bands of ${}^{128}\mathrm{Cs}$ and ${}^{132}\mathrm{La}$ are presented. Experimental reduced transition probabilities in ${}^{128}\mathrm{Cs}$ are compared with theoretical calculations done in the frame of the core-quasiparticle coupling model. The electromagnetic properties, energy and spin of levels belonging to the partner bands show that ${}^{128}\mathrm{Cs}$ is the best known example revealing the chiral symmetry breaking phenomenon.

Figure 1

Total $\gamma$-ray intensity depopulating a given level of the yrast band. Corresponding intensities from the side-feeding model (solid lines) reproduce well the mean tendency of experimental data. Left panel: the dotted and dashed lines were calculated by using the side-feeding parameters adjusted to reproduce the intensity data for even and odd spin levels, respectively.

Figure 2

Partner bands built on the $\pi h_{11/2}\otimes (\nu h_{11/2}{)}^{-1}$ configuration in ${}^{128}\mathrm{Cs}$ and ${}^{132}\mathrm{La}$ observed in the experiment. The arrow widths are proportional to the relative transition probabilities. The sum of transition intensities depopulating the given level is normalized to unity. The lifetime of levels are given in italics under the spins of the corresponding levels.

Figure 3

Doppler broadened line shapes of $\gamma$-transitions registered by groups of detectors placed forward (25° and 38°) and backward (135° and 142°) with respect to the beam direction. Left part: 930 keV ${18}^{+}\to {16}^{+}$ transition in the yrast band of ${}^{128}\mathrm{Cs}$. Right part: 959 keV ${17}^{+}\to {15}^{+}$ transition in the yrast band of ${}^{132}\mathrm{La}$. Bold solid line: Doppler broadened lineshape of the analyzed transition. Dotted line: the contamination peaks. Thin solid line: the result of fit to the experimental data.

Figure 4

$B(E2)$ and $B(M1)$ reduced transition probabilities of ${}^{128}\mathrm{Cs}$ (left part) and ${}^{132}\mathrm{La}$ (right part). Top and middle: $B(E2)$ and $B(M1)$ values for inband transitions of ${}^{128}\mathrm{Cs}$ and ${}^{132}\mathrm{La}$. Bottom: $B(M1)$ values for interband $\mathrm{\text{side}}\to \mathrm{\text{yrast}}$ transitions.

Figure 5

Particle alignment for partner bands of ${}^{128}\mathrm{Cs}$ and ${}^{132}\mathrm{La}$. The used Harris parameters are $J_0=16{\hslash }^2{\mathrm{MeV}}^{-1}$, $J_1=33{\hslash }^4{\mathrm{MeV}}^{-3}$ for ${}^{128}\mathrm{Cs}$ and $J_0=11{\hslash }^2{\mathrm{MeV}}^{-1}$, $J_1=37{\hslash }^4{\mathrm{MeV}}^{-3}$ for ${}^{132}\mathrm{La}$. In distinction from the case of ${}^{134}\mathrm{Pr}$ (Fig. 2, Ref. 9) the particle alignment in both bands of ${}^{128}\mathrm{Cs}$ and ${}^{132}\mathrm{La}$ is very similar.

Figure 6

Comparison of experimental (full circles) and calculated (open circles) absolute transition probabilities for ${}^{128}\mathrm{Cs}$. Top left: $B(E2)$ values in yrast band. Top right: $B(E2)$ values in side band. Middle left and middle right: the same but for $B(M1)$ values. Bottom-left: $B(M1)$ values for interband transitions.