Study of $\tau^- \to\nu_{\tau} \pi^{-}\pi^{0}\ell^{+}\ell^{-}$ decays in the framework of Resonance Chiral Theory

Abstract

In this study, the − → − 0 ℓ + ℓ − (ℓ = , ) processes are analyzed. This are ( 2 )-suppressed with respect to the dominant di-pion tau decay channel. Both the inner-bremsstrahlung and the structure-(and model-)dependent contributions are considered. In the ℓ = case, structuredependent effects are O (1%) in the decay rate, yielding a clean prediction of its branching ratio, 2.3 × 10 −5 , measurable with BaBar or Belle(-II) data. For ℓ = , both contributions have similar magnitude and we get a branching fraction of (1.6 ± 0.3) × 10 −7 , reachable by the end of Belle-II operation. These decays allow to study the dynamics of strong interactions with simultaneous weak and electromagnetic probes; their knowledge will contribute to reducing backgrounds in lepton flavor/number violating searches.