# Dispersive evaluation of the second-class amplitude $\tau\to\eta\pi\nu_\tau$ in the standard model

2 Groupe Théorie
LAL - Laboratoire de l'Accélérateur Linéaire
Abstract : We reevaluate the two form factors relevant for the $\eta\pi$ second-class $\tau$ decay mode, making systematic use of analyticity, unitarity, combined with updated inputs to the NLO chiral constraints. We focus, in particular, on the shape of the $\rho$ resonance peak which is a background-free signature of a second-class current. Its dispersive construction requires the $\eta\pi\to\pi\pi$ scattering amplitude which we derive from a family of Khuri-Treiman equations solutions constrained with accurate recent results on the $\eta\to3\pi$ Dalitz plot.
Document type :
Conference papers

http://hal.in2p3.fr/in2p3-00800969
Contributor : Sabine Starita <>
Submitted on : Thursday, March 14, 2013 - 5:26:07 PM
Last modification on : Wednesday, September 16, 2020 - 5:37:37 PM

### Identifiers

• HAL Id : in2p3-00800969, version 1
• ARXIV : 1303.2879

### Citation

S. Descotes-Genon, E. Kou, B. Moussallam. Dispersive evaluation of the second-class amplitude $\tau\to\eta\pi\nu_\tau$ in the standard model. 12th International Workshop on Tau Lepton Physics (TAU2012), Sep 2012, Nagoya, Japan. ⟨in2p3-00800969⟩

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