Lifetimes, cross sections, and production mechanisms of charmed particles produced by 20-GeV photons

Abstract

Seventy-one events containing charmed-particle decays have been observed in an experiment using the SLAC Hybrid Facility exposed to a backward-scattered photon beam. Several improvements were made to the apparatus since the previous experiment on charm photoproduction. Results for the charmed-meson lifetimes are consistent with the published results from the previous experiment and the two data samples have been combined yielding a total sample of 136 charm events. After imposing rigorous cuts, 50 neutral, 48 charged, and 2 charged/neutral ambiguous decays remain. From these, the charmed-meson lifetimes are measured to be =(8.6\ifmmode\pm\else\textpm\fi{}${1.3}_{\mathrm{\ensuremath{-}}0.3}^{+0}$ $^{.7}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ sec, =(6.1\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}10 $^{\mathrm{\ensuremath{-}}13}$ sec, and their ratio =1.4\ifmmode\pm\else\textpm\fi{}${0.3}_{\mathrm{\ensuremath{-}}}$ $_{0.1}^{+0.2}$. The total charm cross section at a photon energy of 20 GeV has been measured to be (62\ifmmode\pm\else\textpm\fi{}${8}_{\mathrm{\ensuremath{-}}10}^{+15}$) nb. There is evidence for both DD\ifmmode\bar\else\textasciimacron\fi{}X and D\ifmmode\bar\else\textasciimacron\fi{}${\ensuremath{\Lambda}}_{c}^{+}$X production with ${\ensuremath{\sigma}}_{D\ifmmode\bar\else\textasciimacron\fi{}{\ensuremath{\Lambda}}_{c}^{+}X}$/${\ensuremath{\sigma}}_{\mathrm{charm}}$=(71\ifmmode\pm\else\textpm\fi{} 11\ifmmode\pm\else\textpm\fi{}6)%.