J-PARC Experiment E36 at the Nuclear and Particle Physics Facillity

Precise Measurement of Γ (K+→ e+ν)/Γ(K+→ μ+ν)
using Stopped Positive Kaons

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Home > Aim of our experiment > Physics motivation for the heavy sterile neutrino search
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Search for sterile ν in K→μν

In 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

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.