Focal plane instrumentation: A very high resolution MWPC system for inclined tracks

A focal plane system has been developed for the MIT energy-loss magnetic spectrometer. The arrival time information from adjacent wires of one MWPC (s = 2 mm), is used to trace particle trajectories with a position resolution of 120 μm (2σ) and an angular resolution of less than 17 mrad (2σ). The tracks are inclined to the MWPC at about 45°. The readout uses 3 delay lines connected to successive sence wires in a cyclical pattern. Coarse wire positions are determined by differences and drift times by sums of signal arrival times at the ends of the delay lines. A Cherenkov counter provides a fiducial signal. Interpolation is independent of drift velocity since the drift is normal to the sense plane. A similar readout with a second chamber provides position information perpendicular to momentum plane. This information is used to correct on-line for focal plane curvatures and other spectrometer aberrations. Final momentum resolution is about 10−4.