A muon beam polarimeter was built for the SMC experiment at the CERN SPS, f
or beam energies of 100 and 190 GeV. The beam polarisation is determined fr
om the asymmetry in the elastic scattering off the polarised electrons of a
ferromagnetic target whose magnetisation is periodically reversed. At muon
energies of 100 and 190 GeV the measured polarisation is P-mu = -0.80 +/-
0.03 (stat.) +/- 0.02 (syst.) and P-mu = - 0.797 +/- 0.011 (stat.) +/- 0.01
2 (syst.), respectively. These results agree with measurements of the beam
polarisation using a shape analysis of the decay positron energy spectrum.
(C) 2000 Elsevier Science B.V. All rights reserved.