A cylindrical pair spectrometer for the detection of medium energy photons

A large acceptance, medium energy resolution, cylindrical drift chamber has been constructed for use as a pair spectrometer for the detection of 50 to 100 MeV photons from radiative muon capture. Energy resolution for the detection of 129 MeV photons was found to be 12% (FWHM) at a magnetic field of 2.4 kG and 5.5% at 7.1 kG with the resolution improving as the photon energy decreases. The worst case position resolution for particle tracks is 150 microns (σ). The acceptance for the detection of photons over the range 55–83 MeV was found to be 0.66% at 2.4 kG. All of these properties are reproduced by a Monte Carlo simulation of the spectrometer. Triggering schemes and further chamber characteristics will also be discussed.