Apparatus for a search for T-violating muon polarization in stopped-kaon decays

Abstract The detector built at KEK to search for T-violating transverse muon polarization in K + → π 0 μ + ν μ ( K μ 3 ) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the μ + through a toroidal spectrometer and detecting the π 0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance.