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

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±${1.3}_{\mathrm{-}0.3}^{+0\mathrm{}}$ ${}_{}{}^{.7}{}_{}{}^{}$)×${10}^{\mathrm{-}13}$ sec, &=(6.1±0.9±0.3)×10 ${}_{}{}^{\mathrm{-}13}{}_{}{}^{}$ sec, and their ratio &=1.4±${0.3}_{\mathrm{-}}$ ${}_{0.1}{}^{+0.2\mathrm{}}{}_{}{}^{}$. The total charm cross section at a photon energy of 20 GeV has been measured to be (62±$8_{\mathrm{-}10}^{+15\mathrm{}}$) nb. There is evidence for both DD¯X and D¯${\Lambda }_c^{+}$X production with ${\sigma }_{D¯{\Lambda }_c^{+}X}$/${\sigma }_{\mathrm{charm}}$=(71± 11±6)%.