An alternative parametrization of the pion form factor and the mass and width of rho(770)

TL;DR

This paper introduces a new parametrization of the rho(770) meson contribution to the pion form factor, revealing smaller mass values consistent with previous experiments, and emphasizes the importance of parametrization choice in extracting meson properties.

Contribution

It proposes a novel parametrization based on a running mass from a dispersion relation, improving fits and providing more accurate rho(770) mass estimates compared to existing models.

Findings

New parametrization yields smaller rho(770) mass values.

Fits to experimental data are as good or better with the new model.

The model explains discrepancies in rho(770) mass measurements.

Abstract

In order to reveal possible mass shifts of the vector mesons in a dense strongly interacting medium presumably created in high energy heavy ion collisions it is necessary to know their free masses reliably. The rho(770) mass quoted in the last two editions of the Review of Particle Physics is significantly larger than the values quoted in previous editions. The new value is mostly influenced by the results of recent experiments CMD-2 and SND at the VEPP-2M e+e- collider at Novosibirsk. We show that the values of the mass and width of the rho(770) meson measured in the e+e- -> pi+pi- annihilation depend crucially on the parametrization used for the pion form factor. We propose a parametrization of the rho(770) contribution to the pion form factor based on the running mass calculated from a single-subtracted dispersion relation and compare it with the parametrization based on the formula of Gounaris and Sakurai used recently by the CMD-2 collaboration. We show that our parametrization gives equally good or better fits when applied to the data of the CMD-2, SND, and KLOE collaborations, but yields much smaller values of the rho(770) mass, consistent with the photoproduction and hadronic reactions results. Our fit to the KLOE data becomes exceptionally excellent (confidence level of 99.88%) if an energy shift of about 2 MeV in the rho-omega region is allowed.