Implications of the recent high statistics determination of the pion electromagnetic form factor in the timelike region

TL;DR

This paper uses recent high-precision measurements of the pion electromagnetic form factor to derive model-independent constraints on its Taylor expansion coefficients and zero locations, enhancing understanding of its analytic structure.

Contribution

It introduces a method that exploits recent experimental data and phase information to constrain the form factor's Taylor coefficients without relying on specific parametrizations.

Findings

Allowed ranges for curvature and next Taylor coefficient are established.

A large zero-free region in the complex plane for the form factor is identified.

Strong correlation between the Taylor coefficients is demonstrated.

Abstract

The recently evaluated two-pion contribution to the muon g-2 and the phase of the pion electromagnetic form factor in the elastic region, known from \pi\pi scattering by Fermi-Watson theorem, are exploited by analytic techniques for finding correlations between the coefficients of the Taylor expansion at t=0 and the values of the form factor at several points in the spacelike region. We do not use specific parametrizations and the results are fully independent of the unknown phase in the inelastic region. Using for instance, from recent determinations, <r^2_\pi> = (0.435 \pm 0.005) fm^2 and F(-1.6 GeV^2)=0.243^{+0.022}_{-0.014}, we obtain the allowed ranges 3.75 GeV^{-4}\lesssim c \lesssim 3.98 GeV^{-4} and 9.91 GeV^{-6}\lesssim d \lesssim 10.46 GeV^{-6} for the curvature and the next Taylor coefficient, with a strong correlation between them. We also predict a large region in the complex plane where the form factor can not have zeros.