Charm photoproduction at 20 GeV

Abstract

Sixty-two charm events have been observed in an exposure of the SLAC Hybrid Facility toa backward sacttered laser beam. Based on 22 neutral and 21 charged decays we have measured the charmed-meson lifetimes to be ${\ensuremath{\tau}}_{{D}^{0}}=({6.8}_{\ensuremath{-}1.8}^{+2.3})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ sec, ${\ensuremath{\tau}}_{{D}^{\ifmmode\pm\else\textpm\fi{}}}=({7.4}_{\ensuremath{-}2.0}^{+2.3})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ sec and their ratio $\frac{{\ensuremath{\tau}}_{{D}^{\ifmmode\pm\else\textpm\fi{}}}}{{\ensuremath{\tau}}_{{D}^{0}}={1.1}_{\ensuremath{-}0.3}^{+0.6}}$. The inclusive charm cross section at a photon energy of 20 GeV has been measured to be ${56}_{\ensuremath{-}23}^{+24}$ nb. Evidence is presented for a non-$D\overline{D}$ component to charm production, consistent with (35\ifmmode\pm\else\textpm\fi{}20)% ${\ensuremath{\Lambda}}_{c}^{+}$ production and some ${D}^{*\ifmmode\pm\else\textpm\fi{}}$ production. We have found no unambiguous $F$ decays.