Multiparticle identification with ISIS: Tests with the full aperture ISIS 1

Results are reported of a successful test of ISIS 1 in a particle beam. ISIS 1 is a full aperture (4m × 2m) prototype of the particle identifier ISIS (Identification of Secondaries by Ionisation Sampling), proposed for the European Hybrid Spectrometer (EHS) at the SPS at CERN. Using the “relativistic rise” of the ionisation loss, electrons and pions at 500 MeV/c were identified with better than 99% confidence, the data containing typically 5–10 tracks per “picture” drifted by up to 2 m. The ionisation resolution was 12–14% fwhm on 1m of track and the two track resolution was 2 cm. These results, which agree with our predictions, indicate that ISIS 2 with 5 m of useful track length will be able to distinguish uniquely kaons and protons from pions of known momentum in high multiplicity interactions up to 50 and 100 GeV/c respectively.