Interpreting increases in |S_L| due to channel coupling

Mackintosh, R. S. (2013). Interpreting increases in |S_L| due to channel coupling. Physical Review C, 88(5), article no. 054603.

DOI: https://doi.org/10.1103/PhysRevC.88.054603

Abstract

We present various cases where the coupling of breakup or transfer channels to the elastic channel leads to an increase in the elastic channel |S_L| for particular values of L. Particular emphasis is given to ⁶Li, ⁷Be, and ⁸B scattering from ⁵⁸Ni and ⁶He scattering from ²⁰⁸Pb, all near the Coulomb barrier. A link is proposed to the fact that ⁸B has a larger breakup cross section while its elastic scattering angular distribution is less modified by breakup than ⁶Li and ⁷Be at the same energy relative to the barrier; an argument is made relating this to non-local processes. We also describe cases of ⁶He scattering from ²⁰⁸Pb at energies far above the Coulomb barrier, of heavy ion scattering, and of ²H and ³He scattering. The effect is absent in otherwise similar proton scattering cases. The increase in |S_L| is associated with strongly absorptive potentials and excitation processes that keep an excited amplitude of the projectile from the absorptive region prior to de-excitation to the elastic channel. The possible relevance to direct reactions is proposed.

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