Improving the Kpi vector form factor through Kl3 constraints

Abstract

The $K\pi$ vector form factor, $F_{+}^{K\pi }$, used to reproduce the Belle spectrum of $\text{tauKpi}$ decays is described by means of a three-times subtracted dispersion relation also incorporating constraints from $K_{l3}$ decays. The slope and curvature of $F_{+}^{K\pi }$ are fitted to the data yielding ${\lambda }_{+}^{\prime }=(25.49\pm 0.31)\times 10^{-3}$ and ${\lambda }_{+}"=(12.22\pm 0.14)\times 10^{-4}$. The pole parameters of the $K^{\ast }(892{)}^{\pm }$ are found to be $m_{K^{\ast }(892{)}^{\pm }}=892.0\pm 0.5$ MeV and ${\Gamma }_{K^{\ast }(892{)}^{\pm }}=46.5\pm 1.1$ MeV. The phase-space integrals relevant for $K_{l3}$ analyses and the $P$-wave isospin-1/2 $K\pi$ phase-shift threshold parameters are also calculated.

Comments: 3 pages, uses aipproc style. Talk presented by R. Escribano at the IX International Conference on Quark Confinement and Hadron Spectrum (QCHS09), Madrid, Spain, 30.8-3.9.2010