The hypernucleus ${}_{\Lambda }^9\mathrm{Be}$ is investigated using the $\alpha +\Lambda +\alpha$ cluster model. The corresponding Faddeev equations are solved for different $\alpha -\alpha$ and $\Lambda -\alpha$ interactions that describe both ${}^8\mathrm{Be}$ and ${}_{\Lambda }^5\mathrm{He}$ energy spectra. For the ground state $J^{\pi }={\frac{1}{2}}^{+}$ and excited states ${\frac{3}{2}}^{+}$ and ${\frac{5}{2}}^{+}$ we include the Coulomb repulsion between the $\alpha ’\mathrm{s}$ and calculate, in addition to the energy eigenvalues, the Coulomb energy, the $\alpha$- and $\Lambda$-particle mean radius, the rms charge radius, the electric quadrupole moment $\mathrm{}\left(Q\right),$ as well as the magnetic dipole $\left(\mu \right)$ and octopole $\left({\mu }_3\right)$ moments. To the best of our knowledge these observables have not yet been measured and, therefore, our calculation constitutes the first prediction. Structural differences between ${}^9\mathrm{Be}$ and ${}_{\Lambda }^9\mathrm{Be}$ lead to values of Q and $\mu$ that have opposite sign. Unlike previous theoretical work we find only two degenerate negative parity resonances ${\frac{1}{2}}^{-}\left({\frac{3}{2}}^{-}\right)$ but, in addition, we get two degenerate positive parity resonances with $J^{\pi }={\frac{7}{2}}^{+}\left({\frac{9}{2}}^{+}\right)$ at higher energy which, together with the bound states, complete the positive parity rotational band.

• Received 25 March 2002

DOI:https://doi.org/10.1103/PhysRevC.66.014001