Deriving experimental constraints on the scalar form factor in the second-class $\tau \to\eta \pi \nu$ mode
The rare second-class decay mode of the $\tau$ into $\eta\pi\nu$ could be observed for the first time at Belle II. It is important to try to derive a reliable evaluation of the branching fraction and of the energy distribution of this mode within the standard-model. Many predictions exist already in...
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| Format: | Article |
| Language: | English |
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SciPost
2025-07-01
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| Series: | SciPost Physics Proceedings |
| Online Access: | https://scipost.org/SciPostPhysProc.16.009 |
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| Summary: | The rare second-class decay mode of the $\tau$ into $\eta\pi\nu$ could be observed for the first time at Belle II. It is important to try to derive a reliable evaluation of the branching fraction and of the energy distribution of this mode within the standard-model. Many predictions exist already in the literature which can differ by one to two orders of magnitude. Here, an approach based on a systematic use of the property of analyticity of form factors and scattering amplitudes in QCD is discussed. In particular, we will show that the scalar form factor in the $\tau$ decay can be related to photon-photon scattering and radiative $\phi$ decay amplitudes for which precise experimental measurements have been performed by the Belle and KLOE collaborations. |
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| ISSN: | 2666-4003 |