Study of τ− → π−ℓ+ℓ−ντ at Belle

Abstract

The rare tau decay τ−→π−ℓ+ℓ−ντ(ℓ=e,μ) is an ideal probe of the γ⁎W⁎π vertex. The knowledge of the γ⁎W⁎π vertex in the full kinematical range is important to test QCD predictions as well as to evaluate the hadronic light-by-light contributions to the muon anomalous magnetic moment. Based on the recently published analytical formalism for this decay in the framework of the Chiral Perturbation Theory, a Monte Carlo event generator was developed and embedded in TAUOLA program. Given the large statistics of about 9×108τ+τ− pairs collected at Belle, it becomes possible to study this decay with the accuracy of about few percent. We report the current status of the analysis at Belle.