DOI 10.1007/s100529901101
Factorisation in higher-twist single-spin amplitudes
P.G. Ratcliffe1,2
1 Dipartimento di Scienze,
Università dell'Insubria - sede di Como,
via Lucini 3, I-22100 Como, Italy
2 Istituto Nazionale di Fisica Nucleare - sezione di Milano, Italy
Received: 31 July 1998 / Revised version: 12 November 1998 / Published online: 11 March 1999
Abstract
We analyse the twist-three amplitudes that can give rise to
single-spin asymmetries in hadron-hadron scattering; in so doing we
bring to light a novel factorisation property. As already known, the
requirement of an imaginary part leads to consideration of
twist-three contributions that are also related to transverse spin
in deep-inelastic scattering. In particular, when an external line
becomes soft in contributions arising from three-parton correlators,
the imaginary part of an internal propagator may be exposed. As
shown here, it is precisely this kinematical configuration that
permits the factorisation. An important feature is the resulting
simplification: the calculation of tens of Feynman diagrams normally
contributing to such processes is reduced to the evaluation of
products of the simple factors derived here and known two-body
helicity amplitudes. We thus find clarifying relations between the
spin-dependent and spin-averaged cross-sections and formulate a
series of selection rules. In addition, the kinematical dependence
of such asymmetries, is rendered more transparent.
Author for correspondance: pgr@fis.unico.it
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