A search for T-violating transverse muon polarization (PT ) in the K + → π 0 µ + ν decay was performed using kaon decays at rest. A new improved value, PT = −0.0017 ± 0.0023(stat) ± 0.0011(syst), was obtained giving an upper limit, |PT | < 0.0050. The T-violation parameter was determined to be Imξ = −0.0053 ± 0.0071(stat) ± 0.0036(syst) giving an upper limit, |Imξ| < 0.016. PACS numbers: 11.30.Er, 12.60.Fr, 13.20.Eb The transverse muon polarization, P T , in the) decay is one of the observables of CP violation beyond the standard model (SM). CP violation in general is a subject of continuing interest in K and B meson decays. P T , defined as the polarization component perpendicular to the decay plane, is an obvious signature of a violation of time reversal (T) invariance, since the spurious effect from final state interactions is very small (< 10 −5 ) [1]. P T is almost vanishing (∼ 10 −7 ) in the SM with the Kobayashi-Maskawa scheme [2]; it is therefore a very sensitive probe of CP violation mechanisms beyond the SM and new physics along with B physics such as b → sγ and some other decays [3]. Models [4] such as those with multi-Higgs doublets or leptoquarks, or some SUSY may to give rise to P T as large as 10 −3 .At the High Energy Accelerator Research Organization (KEK) the E246 collaboration has been performing a search for P T in K + µ3 . In 1999, the first result was published [5] based on ∼ 3.9 × 10 6 good K + µ3 events from the data taken during 1996 and 1997, indicating no evidence for T violation. Further runs provided a cumulative data sample with three times more events. This Letter constitutes our final result from all the data with an improved analysis. The present result supersedes all our earlier reports.
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