Relativistic charged particle identification with ISIS2

The operation of the ISIS2 pictorial drift chamber in the European Hybrid Spectrometer at the CERN SPS is described. The data analysis and calibration procedure are outlined. After a brief presentation of the quality of the spatial data from the chamber, the dE/dx data are treated in some detail. It is shown that an ionisation resolution of 3.5% rms (or 8.3% fwhm) is routinely obtained on a large majority of tracks entering the 8 m2 acceptance of the device; this is within 20% of the theoretical limit of the performance. Samples of tracks identified as electrons, pions or protons by kinematic fitting to conversions or strange particle decays are used to check the quality of the mass identification. Misidentification rates and confidence levels for mass separation as a function of momentum for each mass pair are given. Some data are given on the effects of space charge and a measurement of the relativistic rise is reported. (orig.)