PROMPT PHOTON ENERGY-SPECTRA IN B-DECAYS AND DETERMINATION OF THE CKM MATRIX-ELEMENTS

We present theoretical estimates of the inclusive prompt photon energy spectrum in direct decays of B-hadrons through the charged current processes B --> X(c) + gamma and B --> X(u) + gamma, and the flavour changing neutral current (FCNC) B --> X(s) + gamma and B --> X(d) + gamma (here the subscript q on X(q) denotes the quark flavour in the transition b --> q). It is argued that the various components in the inclusive spectrum can, in principle, be disentangled using the photon energy and flavour tagging the hadron(s) recoiling against the photon in B-decays, thereby providing a new technique to determine the CKM matrix elements \ V(cb) \, \ V(ub) \, \ V(ts) \, and \ V(td) \. In particular, the high energy part of the inclusive photon energy spectrum being dominated by the electromagnetic penguins could provide the first direct measurement of the CKM matrix element \ V(ts) \. We quantify this by firming up predictions for the inclusive decays B --> X(s) + gamma in the standard model.