Vector form factor of the pion : A model-independent approach

Abstract

We study a model-independent parameterization of the vector pion form factor that arises from the constraints of analyticity and unitarity. Our description should be suitable up to √s 1.2 GeV and allows a model-independent determination of the mass of the (770) resonance. We analyse the experimental data on τ− → π−π0ντ and e+e− → π+π− in this framework, and its consequences on the low-energy observables worked out by chiral perturbation theory. An evaluation of the two pion contribution to the anomalous magnetic moment of the muon, aμ, and to the fine structure constant, α(MZZ2), is also performed.