Three-body calculation of the structure of _Λ⁹Be

The hypernucleus _Λ⁹Be is investigated using the α+Λ+α cluster model. The corresponding Faddeev equations are solved for different α-α and Λ-α interactions that describe both ⁸Be and _Λ⁵He energy spectra. For the ground state J^π=1 / 2⁺ and excited states 3 / 2⁺ and 5 / 2⁺ we include the Coulomb repulsion between the α’s and calculate, in addition to the energy eigenvalues, the Coulomb energy, the α- and Λ-particle mean radius, the rms charge radius, the electric quadrupole moment (Q), as well as the magnetic dipole (μ) and octopole (μ₃) 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 ⁹Be and _Λ⁹Be lead to values of Q and μ that have opposite sign. Unlike previous theoretical work we find only two degenerate negative parity resonances 1 / 2^-(3 / 2^-) but, in addition, we get two degenerate positive parity resonances with J^π=7 / 2⁺(9 / 2⁺) at higher energy which, together with the bound states, complete the positive parity rotational band.