The ${}^9$Be photodisintegration cross section within Cluster Effective Field Theory

Abstract: A low-energy calculation of ${}^9$Be photodisintegration cross section is presented within an $\alpha\alpha n$ cluster approach. The $\alpha n$ and $\alpha\alpha$ contact interactions are derived from cluster effective field theory. The two-body potentials defined in momentum space are regularized by a Gaussian cutoff. The associated low-energy constants are found by comparing the calculated low-energy T-matrix with its effective range expansion. A three-body state-dependent potential is also introduced in the model. First, the ${}^9$Be three-body binding energy is studied within the non-symmetrized hyperspherical harmonics method. Then, the low-energy cross section is calculated via the Lorentz integral transform method, focussing on the dominant electric dipole transitions. A twofold evaluation of the nuclear current matrix element is presented, employing both the electric dipole transition operator (Siegert theorem) and the one-body convection current operator. This approach is adopted to allow for a discussion of the effect of the many-body currents.