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