Photoproduction of charmed particles in nuclear emulsion coupled to the Omega Prime spectrometer. Description of the experimental method

Abstract

The hybridized system including the nuclear-emulsion target and the magnetic Omega Prime spectrometer is described. The set-up was used in a CERN experiment for the measurement of lifetimes of charmed particles produced by tagged photons from the bremsstrahlung beam. The emulsion served simultaneously as a target and as a high-spatial-resolution vertex detector in order to recognize decay vertices and measure decay distances of charmed particles. In order to avoid the blackening of the emulsion due to electromagnetic interactions the targets were delivered into the beam position one at a time and removed automatically after suitable dosage. The Omega Prime spectrometer allowed the determination of the parameters of the secondary particles and the reconstruction of the interaction points in the emulsion with a high precision. The method used was very successful in finding photohadronic events and in separating a practically background free subsample with the production of pairs of charmed particles decaying inside the emulsion.