Search for sterile ν in K→μνIn the TREK experiment, we will search for the transverse muon polarization in K+ → π0μ+ν by measuring the μ+ momentum, π0 momentum, and μ+ polarization. Therefore, the TREK apparatus is very suited for the heavy neutrino search because
The μ+ momentum generated from the K+ → μ+N decay is monochromatic. A peak structure is formed in the momentum spectrum.
The μ+ polarization in the direction of μ+ motion depends on neutrino masses and N production mechanism.
In addition to the detector system for the Γ(Ke2)/Γ(Kμ2) measurement,
which consist of the toroidal spectrometer and the CsI(Tl) calorimeter, the muon polarimeter will be used for the measurement of the longitudinal muon polarization.
Two settings of the magnetic fields B = 1.4 T and 0.65 T will be chosen to cover a wide μ+ momentum region. The μ+ momentum is analyzed by the spectrometer and the μ+ is identified by the TOF measurement. After passing through the spectrometer,
the muons are slowed down by a copper degrader and stop in the polarimeter.
The magnetic field from the spectrometer magnet is shielded by adding new
iron plates and an external decouping field of ≈10 Gauss is applied to
preserve the muon polarization in longitudinal direction. The muon polarization
in the longitudinal direction is measured as position asymmetry from μ+ → e+νν in forward and backward directions.