A large acceptance spectrometer for the internal target facility at NIKHEF

A non-focusing magnetic spectrometer, BigBite, has been built for use at the Internal Target Facility of the AmPS ring at NIKHEF. It allows detection of particles with momentum in the range of 200–900 MeV/c, with an angular resolution of about 4 mrad, and a design momentum resolution of 5 × 10−3. The track of a particle after passage through the field of a single dipole magnet is determined by two multi-wire drift chambers each of which has two planes. The four planes contain a total of 338 sense wires. For each plane, both sense wires and cathode strips are used to make measurements of each coordinate. The trigger consists of coincident signals from a single scintillator and a diffusely reflecting aerogel Cherenkov detector. The latter also provides discrimination between electrons and pions. Details of the signal handling and first results on the performance of the complete system will be discussed.