Constraining the Kpi vector form factor by tau---> K pi nu_tau and K_l3 decay data

TL;DR

This paper uses a dispersive approach to analyze $K o\pi$ form factors and decay data, extracting key parameters like slope, curvature, and resonance properties, improving understanding of kaon-pion interactions.

Contribution

It introduces a dispersive representation constrained by tau and kaon decay data, providing precise form factor parameters and resonance characteristics.

Findings

Determined slope and curvature of $F_+^{K o\pi}$ from data.

Calculated phase-space integrals for $K_{l3}$ decays.

Extracted mass and width of $K^*(892)^\pm$ resonance.

Abstract

A subtracted dispersive representation of the $K\pi$ vector form factor, $F_+^{K\pi}$, is used to fit the Belle spectrum of $\tauKpi$ decays incorporating constraints from results on $K_{l3}$ decays. Through the use of three subtractions, the slope and curvature of $F_+^{K\pi}$ are obtained directly from the data yielding $\lambda_+'=(25.49 \pm 0.31) \times 10^{-3}$ and $\lambda_+"= (12.22 \pm 0.14) \times 10^{-4}$. The phase-space integrals relevant for $K_{l3}$ analyses are calculated. Additionally, from the pole position on the second Riemann sheet the mass and width of the $K^*(892)^\pm$ are found to be $m_{K^*(892)^\pm}= 892.0\pm 0.5$ MeV and $\Gamma_{K^*(892)^\pm}= 46.5 \pm 1.1$ MeV. Finally, we study the $P$-wave isospin-1/2 $K\pi$ phase-shift and its threshold parameters.