CP violation in the Cabbibo-suppressed decay τ→ Kπντ with polarized τ leptons

Abstract

CP violation from physics beyond the Standard Model (SM) is investigated in the Cabbibo-suppressed decay τ→ Kπν τ with polarized τ leptons, to which both the J P=1 − resonance K ∗ and the J P=0 + resonance K ∗ 0 contribute. In addition to the CP-odd rate asymmetry, τ polarization enables us to construct three additional CP-odd polarization asymmetries that can be enhanced due to the interference between the K ∗ and K ∗ 0 , and whose magnitudes depend crucially on the K ∗ 0 decay constant, f K ∗ 0 . Taking a QCD sum rule estimate of f K ∗ 0 =45 MeV and the present experimental constraints on the CP-odd parameters into account, we estimate quantitatively the maximally-allowed values for the CP-odd rate and polarization asymmetries in the multi-Higgs-doublet (MHD) model and the scalar-leptoquark (SLQ) models consistent with the SM gauge symmetry where neutrinos are massless and left-handed as in the SM. We find that the CP-odd rate and polarization asymmetries are of a similar size for highly-polarized τ leptons and, for their maximally-allowed values, CP violation in the MHD model and two SLQ models may be detected with about 10 6 and 10 7 τ's at the 1 σ level.