7Be(p,γ)8B S factor from ab initio no-core shell model wave functions

Nuclear structure of Be-7, B-8, and Li-7,Li-8 is studied within the ab initio no-core shell model (NCSM). Starting from high-precision nucleon-nucleon (NN) interactions, wave functions of Be-7 and B-8 bound states are obtained in basis spaces up to 10h Omega and used to calculate channel cluster form factors (overlap integrals) of the B-8 ground state with Be-7+p. Due to the use of the harmonic oscillator (HO) basis, the overlap integrals have incorrect asymptotic properties. We fix this problem in two alternative ways. First, by a Woods-Saxon potential solution fit to the interior of the NCSM overlap integrals. Second, by a direct matching with the Whittaker function. The corrected overlap integrals are then used for the Be-7(p,gamma)B-8 S-factor calculation. We study the convergence of the S factor with respect to the NCSM HO frequency and the model space size. Our S factor results agree with recent direct measurement data. We also test the spectroscopic factors and the corrected overlap integrals from the NCSM in describing the momentum distributions in knockout reactions with B-8 projectiles. A good agreement with the available experimental data is also found, attesting to the overall consistency of the calculations.