Open questions and perspectives for hadron electromagnetic form factors in space–like and time–like regions

E. Tomasi–Gustafsson

DAPNIA/SPhN, CEA/Saclay, 91191 Gif–sur–Yvette Cedex, France, e–mail: etomasi@cea.fr

Recibido el 31 de enero de 2006
Aceptado el 31 de marzo de 2006

Abstract

An overview of recent data on electromagnetic hadron form factors is presented and discussed in terms of selected nucleon models in space–like and time–like regions. Model independent properties connecting scattering and annihilation channels are presented and give a deeper understanding of the underlying physics. Radiative corrections are discussed. The interest of polarization observables with respect to model predictions and reaction mechanism (one photon versus two photon exchange) is highlighted.

Keywords: Elastic electron scattering; electromagnetic form factors; polarization in interactions and scattering.

Resumen

Se revisan los datos experimentales de los factores de forma electromagnéticos y se estudian dichos factores de forma en varios modelos del nucleón en la región espacialoide y temporaloide. Se presentan algunas propiedades, que son independientes de modelos particulares, que conectan los canales de dispersión y aniquilación y que proveen un mejor entendimiento de la física. Se discuten las correcciones radiativas. Se enfatiza la importancia de observables de polarización para comprobar las predicciones de modelos del nucleón así como los mecanismos de reacciones (intercambio de un foton versus de dos fotones).

Descriptores: Dispersión elástica de electrones; factores de forma electromagnéticos; polarización en interacciones y dispersión.

PACS: 25.30.Bf; 13.40.–f; 13.40.Gp

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Acknowledgements

Most part of the work presented here was done in collaboration or inspired by enlightning discussion with M.P. Rekalo. Thanks are due to G.I. Gakh, for a careful reading of the manuscript and useful remarks, and to E.A. Kuraev for suggesting the structure function method, in the calculation of radiative corrections.

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