Parity reversal of ${}_{\Lambda }^{12}\mathrm{Be}$

We study the spectrum of ${}_{\Lambda }^{12}\mathrm{Be}$ by using an extended version of antisymmetrized molecular dynamics for hypernuclei. Our result indicates that the $\Lambda$-particle impurity effect causes the positive-parity ground state of ${}_{\Lambda }^{12}\mathrm{Be}$ to revert to the normal state, i.e., negative parity. This parity reversion is attributed to the difference in the $\Lambda$ binding energy between the positive- and negative-parity states, which in turn originates in the difference in $\alpha$ clustering and deformation.

Figure 1

(a) Observed spectra of ${}^{13}\mathrm{C}$ and ${}^{11}\mathrm{Be}$. (b) Spectrum of ${}^{11}\mathrm{Be}$ calculated by AMD. (c) Spectra of ${}_{\Lambda }^{12}\mathrm{Be}$ calculated by HyperAMD with the four different $\Lambda N$ interactions given in the figure.

Figure 2

Matter $\left({\rho }_m\right)$ and proton $\left({\rho }_p\right)$ density distributions for the bandhead states of ${}^{11}\mathrm{Be}$ and ${}_{\Lambda }^{12}\mathrm{Be}$. Color plots show the density distribution of the $\Lambda$ particle.

Figure 3

The $\Lambda$ binding energy of the $0_1^{-}$ and $0_1^{+}$ states as function of proton quadrupole deformation $\mathrm{parameter}\beta$. Lines in the figure denote the deformation parameter of $0_1^{\pm }$ states given in Table 1.