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 (4 m*2 m) 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 1 m 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. (14 refs).