Eur. Phys. J. A (2007) 31: 9-14
https://doi.org/10.1140/epja/i2006-10152-3

Regular Article - Nuclear Structure and Reactions

Polarisation observables in lepton-antilepton-to-proton-antiproton reactions including lepton mass

Trinity College, School of Mathematics, Dublin, Ireland

^* e-mail: elise@maths.tcd.ie

Received: 20 July 2006
Accepted: 30 November 2006
Published online: 9 January 2007

Abstract

General expressions, including the lepton mass, for the spin-averaged differential cross-section for the annihilation reaction lepton-antilepton to proton-antiproton are given, as well as general formulae for the single- and double-spin asymmetries in the centre-of-mass frame. In particular, we discuss the single-spin asymmetry, normal to the scattering plane, which measures the relative phase difference between nucleon electromagnetic form factors G_E and G_M. Recent experimental investigations of these form factors in the space- and time-like region are reviewed. It is thought that measurements of the phase of these form factors will provide fundamental information on the internal nucleon structure. The phases between G_E and G_M are accessible through polarisation observables measured in the antiproton-proton-to-lepton-antilepton reaction, or in its time-reversed process.