Measurement of the polarisation of a high energy muon beam

Abstract A muon beam polarimeter has been built for the SMC experiment at the CERN SPS, for muon energies of 100 to 200 GeV. The beam polarisation is determined from the energy spectrum of positrons from the decay μ + → e + ν c ν μ . A polarisation of − 0.82 is measured with a relative systematic accuracy of 3%.