On extraction of twist-two Compton form factors from DVCS observables through harmonic analysis
Kyle Shiells, Yuxun Guo, Xiangdong Ji
Abstract
A bstract We investigate the exercise of locally extracting the real and imaginary parts of the four twist-2 Compton form factors (CFFs) $$ \left\{\mathcal{H},\mathcal{E},\overset{\sim }{\mathcal{H}},\overset{\sim }{\mathcal{E}}\right\} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mi>H</mml:mi> <mml:mi>E</mml:mi> <mml:mover> <mml:mi>H</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mover> <mml:mi>E</mml:mi> <mml:mo>~</mml:mo> </mml:mover> </mml:mfenced> </mml:math> which arise in the deeply virtual Compton scattering (DVCS) process e + p → e + p + γ . Neglecting dynamical higher-twist contributions, we find that there are a sufficient number of DVCS observables and degrees of freedom to extract all 8 leading quantities model-independently, exploiting the azimuthal dependence of the absolute cross sections across all possible beam and target polarizations at a common kinematical point in { Q, t, x B , y }. As an example, for typical JLab lab-frame kinematics, we simplify the reduced DVCS observables to their dominant terms, providing a sufficient number of equations for local determination of the twist-2 CFFs. We demonstrate the feasibility using harmonic fitting to both cross sections and beam spin asymmetries with both real and pseudo-data.