Charmed-particle photoproduction cross section at 20 GeV/c

The charmed-particle photoproduction cross section at 20 GeV/c has been measured using data from the BC72/73 experiment at the SLAC Hybrid Facility. A 1-meter rapid-cycling hydrogen bubble chamber was exposed to a 20 GeV/c backscattered photon beam. Photographs were taken whenever the downstream electronic counters found evidence for a hadronic interaction in the bubble chamber. The SLCA Hybrid Facility was modified to make use of high resolution bubble chamber techniques in order to permit visual identification of a significant fraction of charmed-particle decays. Based on 40 observed charmed-particle decays which passed all the imposed cuts, a charm cross section was obtained. The validity of this result is essentially independent of assumptions regarding the hadronization of charmed quarks. The interpretation of the results is discussed. Particular atention is given to the photon-gluon fusion model. Extensive discussion of a pair-spectrometer beam monitor is included. Drift chambers and scintillators were used to detect e+e- pairs generated within a thin foil placed in the photon beam line