Eur. Phys. J. A (2005) 26: 285-291
https://doi.org/10.1140/epja/i2005-10164-5

Original Article

Asymptotic behavior of nucleon electromagnetic form factors in time-like region

DAPNIA/SPhN, CEA/Saclay, 91191, Gif-sur-Yvette Cedex, France

^* e-mail: etomasi@cea.fr

Received: 19 September 2005
Accepted: 11 October 2005
Published online: 17 November 2005

Abstract

We study the asymptotic behavior of the ratio of Pauli and Dirac electromagnetic nucleon form factors, F ₂/F ₁, in time-like region, for different parametrizations built for the space-like region. We investigate how fast the ratio F ₂/F ₁ approaches the asymptotic limits according to the Phragmèn-Lindelöf theorem. We show that the QCD-inspired logarithmic behavior of this ratio results in very far asymptotics, experimentally unachievable. This is also confirmed by the normal component of the nucleon polarization, P_y, in e ⁺ + e ^-↦N + ¯ (in collisions of unpolarized leptons), which is a very interesting observable, with respect to this theorem. Finally we observe that the 1/Q parametrization of F ₂/F ₁ contradicts this theorem.