https://doi.org/10.1140/epjc/s10052-008-0834-9
Regular Article - Theoretical Physics
K π vector form factor, dispersive constraints and τ→ν τ K π decays
1
Grup de Física Teòrica and IFAE, Universitat Autònoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
2
Institució Catalana de Recerca i Estudis Avançats (ICREA), Grup de Física Teòrica and IFAE, Universitat Autònoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
* e-mail: Rafel.Escribano@ifae.es
Received:
29
October
2008
Revised:
13
November
2008
Published online:
16
December
2008
Recent experimental data for the differential decay distribution of the decay τ
−→ν
τ
K
S
π
− by the Belle collaboration are described by a theoretical model which is composed of the contributing vector and scalar form factors F
+
K
π
(s) and F
0
K
π
(s). Both form factors are constructed such that they fulfil constraints posed by analyticity and unitarity. A good description of the experimental measurement is achieved by incorporating two vector resonances and working with a three-times-subtracted dispersion relation in order to suppress higher-energy contributions. The resonance parameters of the charged K
*(892) meson, defined as the pole of F
+
K
π
(s) in the complex s-plane, can be extracted, with the result
and
. Finally, employing a three-times-subtracted dispersion relation allows one to determine the slope and curvature parameters λ′+=(24.7±0.8)×10−3 and λ″+=(12.0±0.2)×10−4 of the vector form factor F
+
K
π
(s) directly from the data.
© Springer-Verlag , 2009
