# The 16th International Workshop on Tau Lepton Physics (TAU2021) (Virtual Edition)

September 27, 2021 to October 1, 2021
Indiana University
America/Indiana/Indianapolis timezone

## On the scalar $\pi K$ form factor beyond the elastic region

Sep 29, 2021, 9:25 AM
20m
Virtual (Indiana University)

### Virtual

#### Indiana University

Oral contribution Tau2021 Abstracts

### Speaker

Frederic Noël (Universität Bern)

### Description

Pion-kaon ($\pi K$) pairs occur frequently as final states in heavy-particle decays.
A consistent treatment of $\pi K$ scattering and production amplitudes over a wide energy range is therefore mandatory for multiple applications:
in Standard Model tests; to describe crossed channels in the quest for exotic hadronic states; and for an improved spectroscopy of excited kaon resonances.

In the elastic region, the phase shifts of $\pi K$ scattering in a given partial wave are related to the phases of the respective $\pi K$ form factors by Watson's theorem.
Going beyond that, we constructed in Ref.[1] a representation of the scalar $\pi K$ form factor that includes inelastic effects via resonance exchange, while fulfilling all constraints from $\pi K$ scattering and maintaining the correct analytic structure.

As a first application, we considered the decay ${\tau\to K_S\pi\nu_\tau}$, in particular, we studied to which extent the $S$-wave $K_0^*(1430)$ and the $P$-wave $K^*(1410)$ resonances can be differentiated and provide an improved estimate of the $CP$ asymmetry produced by a tensor operator.

[1] Von Detten, L. and Noël, F. and Hanhart, C. and Hoferichter, M. and Kubis, B.
Eur. Phys. J. C 81, 420 (2021); DOI: 10.1140/epjc/s10052-021-09169-7