Abstract
We study the wide angle Compton scattering process on a proton within the soft-collinear factorization (SCET) framework. The main purpose of this work is to estimate the effect due to certain power suppressed corrections. We consider all possible kinematical power corrections and also include the subleading amplitudes describing the scattering with nucleon helicity flip. Under certain assumptions we present a leading-order factorization formula for these amplitudes which includes the hard- and soft-spectator contributions. We apply the formalism and perform a phenomenological analysis of the cross section and asymmetries in the wide angle Compton scattering on a proton. We assume that in the relevant kinematical region where $$-t,-u>2.5$$ GeV $$^{2}$$ the dominant contribution is provided by the soft-spectator mechanism. The hard coefficient functions of the corresponding SCET operators are taken in the leading-order approximation. The analysis of existing cross section data shows that the contribution of the helicity-flip amplitudes to this observable is quite small and comparable with other expected theoretical uncertainties. We also show predictions for double polarization observables for which experimental information exists.
Highlights
Wide angle Compton scattering (WACS) on a proton is one of the most basic processes within the broad class of hard exclusive reactions aimed at studying the partonic structure of the nucleon
We investigate if one can obtain an estimate of the helicity flip amplitudes from the cross section data
In this work we presented a phenomenological analysis of the cross section and asymmetries of WACS in which we accounted for different power suppressed contributions
Summary
Wide angle Compton scattering (WACS) on a proton is one of the most basic processes within the broad class of hard exclusive reactions aimed at studying the partonic structure of the nucleon. It was found that the leading-twist contribution described by the hard two-gluon exchange between three collinear quarks predicts much smaller cross sections than is observed in experiments. Several phenomenological considerations, including the large value of the asymmetry KLL [3] indicate that the dominant contribution in the relevant kinematic range can be provided by the so-called soft-overlap mechanism In this case the underlying quark–photon scattering is described by the handbag diagram with one active quark while the other spectator quarks are assumed to be soft. As a first step toward a proof of the factorization we restrict our attention only to the relevant operators which appear in the leading-order approximation in αs Assuming that such soft contributions are dominant we estimate their possible numerical impact on the cross section and asymmetries.
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