FIRST MEASUREMENT OF THE EXCLUSIVE (P,E(-)) REACTION()E()

We present the first data on the exclusive (p, e(+)e(-)) reaction in a nucleus. Cross sections for populating the ground state and first exc ited state in the residual nucleus are presented for the reaction B-11 (p, e(+)e(-))C-12 at 98 MeV. The e(+)e(-) momentum vectors were measur ed with a high-resolution magnetic pair spectrometer. The distribution s of the virtual photon invariant mass and of the direction of the ele ctron in the virtual photon rest system are compared with a simple sin gle-nucleon model. The (p, e+e-) cross sections are compared with corr esponding data for the (p, gamma) reaction obtained with the same appa ratus. The (p, e(+)e(-)) cross sections show substantial enhancement o ver what is expected from the simple model.