Abstract
Having in mind the well-known limitations of certain models of generalized parton distributions (GPDs), we show that the allegedly universal GPDs, describing both deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP) data, fail to describe measurements of deep inelastic scattering. We present a new global DVCS fit that describes reasonably the world data set, which includes now also new measurements from Hall A and CLAS collaborations. We also explicitly illustrate that Compton form factors (CFFs) cannot be unambiguously extracted from photon electroproduction measurements off unpolarized proton alone and we argue that it is more reliable to interpret such measurements in terms of certain CFF combinations, where still some care is needed in order to estimate the propagated error.
Highlights
The deeply virtual Compton scattering (DVCS) process off a nucleon target is considered to be the theoretically cleanest process allowing access to generalized parton distributions (GPDs) from experimental measurements
We compared model predictions with the new DVCS measurements from the CLAS and Hall A collaborations where we utilize a Fourier transform as filter to strengthen the discriminating power of predictions
We presented a new global DVCS fit KM15 showing that superseding 2006 Hall A cross section data with new one relieves some tensions, but description of first cosine harmonic of
Summary
The deeply virtual Compton scattering (DVCS) process off a nucleon target is considered to be the theoretically cleanest process allowing access to generalized parton distributions (GPDs) from experimental measurements. The remaining four transverse helicity photon flip CFFs appear in the partonic description at next-to-leading order accuracy via the gluon transversity GPDs which might be to a larger extent contaminated by 1/Q2 power suppressed contributions. The DVCS process is measurable in the leptoproduction of a photon on a nucleon (or nucleus) target and it interferes with the Bethe-Heitler process, which is parameterized in terms of the electromagnetic form factors. Physics Opportunities at an Electron-Ion Collider while those of the squared DVCS term are given in terms of bilinear (linear in both CFFs and their complex conjugates) combinations.
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