Dipole strengths in [sup 11]Be from electroproduction of charged pions

The dipole resonances in the light nucleus [sup 11]Be were studied measuring the energy spectra and angular distributions of charged pions in the spin-flip charge-exchange reaction [sup 11]B([ital e],[pi][sup +])[sup 11]Be at [ital E][sub [ital e]]=200 MeV. The ground state and eight excited states below [ital E][sub [ital x]]=18 MeV in [sup 11]Be were observed. The angular distributions were analyzed within the framework of the distorted-wave impulse approximation. A considerable amount of the deduced [ital E]1 strengths is distributed over excitation energies much lower than 18 MeV in [sup 11]Be. The energy distributions of the [ital E]1 strengths of transitions to the [ital s]- and [ital d]-shell states were compared with the results of theoretical calculations with the effect of loosely bound neutron states.