dE/dx measurement in a He-based gas mixture

Abstract The performance of a prototype drift chamber operating in a He-based gas mixture as a specific ionisation detector is presented. In spite of the small number of primary ions, Helium performs quite satisfactorily in measuring energy losses for charged particles: with 50 GeV/ c pions, we have measured in a 90% He–10%  i C 4 H 10 mixture a relative energy loss resolution of 3.1% with 75 samples 3 cm long, using a modified Truncated Mean technique with 80% accepted fraction. The dependence of the resolution on several parameters such as the operating voltage, the truncation fraction, the number and length of the samples is discussed.