Determination of proton electromagnetic form factors from DVCS measurements

We present a detailed analysis of the proton electromagnetic form factors (FFs) using exclusive photon leptoproduction (EP) data in kinematic regions where the Bethe-Heitler (BH) contribution dominates the deeply virtual Compton scattering (DVCS) cross section. By exploiting the sensitivity of the BH amplitude to the Dirac and Pauli FFs, we extract <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>F</a:mi> <a:mn>1</a:mn> </a:msub> <a:mo stretchy="false">(</a:mo> <a:mi>t</a:mi> <a:mo stretchy="false">)</a:mo> </a:math> , <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msub> <e:mi>F</e:mi> <e:mn>2</e:mn> </e:msub> <e:mo stretchy="false">(</e:mo> <e:mi>t</e:mi> <e:mo stretchy="false">)</e:mo> </e:math> , and the corresponding Sachs FFs within several fitting scenarios based on dipole and <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>P</i:mi> </i:math> -pole parametrizations, and evaluate the charge and magnetic radii of the proton. In this fitting scenario, we show that EP measurements in the range <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mn>0.11</k:mn> <k:mo>&lt;</k:mo> <k:mo stretchy="false">|</k:mo> <k:mi>t</k:mi> <k:mo stretchy="false">|</k:mo> <k:mo>&lt;</k:mo> <k:mn>0.45</k:mn> <k:mtext> </k:mtext> <k:mtext> </k:mtext> <k:msup> <k:mi>GeV</k:mi> <k:mn>2</k:mn> </k:msup> </k:math> can provide constraints on <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mi>F</o:mi> <o:mn>1</o:mn> </o:msub> <o:mo stretchy="false">(</o:mo> <o:mi>t</o:mi> <o:mo stretchy="false">)</o:mo> </o:math> , while offering limited sensitivity to <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:msub> <s:mi>F</s:mi> <s:mn>2</s:mn> </s:msub> <s:mo stretchy="false">(</s:mo> <s:mi>t</s:mi> <s:mo stretchy="false">)</s:mo> </s:math> . The extracted charge radius values tend to be smaller than those obtained from traditional elastic electron-proton scattering measurements and are consistent, within uncertainties, with recent high-precision PRad results. These findings indicate that EP measurements, especially when covering smaller values of <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"> <w:mo stretchy="false">|</w:mo> <w:mi>t</w:mi> <w:mo stretchy="false">|</w:mo> </w:math> , can serve as a complementary tool for determining the proton electromagnetic structure and may contribute to ongoing efforts to better understand the proton charge radius. The methodology developed here provides a framework for future combined analyses of EP and elastic electron-proton scattering data which enables a unified determination of the nucleon FFs.