Near-threshold heavy quarkonium photoproduction in a light-front spectator model

The near-threshold photo- and electroproduction of heavy vector quarkonia off the proton provides direct access to its gluonic structure. In particular, the cross section for <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>J</a:mi> <a:mo>/</a:mo> <a:mi mathvariant="normal">Ψ</a:mi> </a:math> photoproduction near threshold is governed by the proton’s gluon gravitational form factors (GFFs). In this work, we employ the leading-order generalized parton distribution framework, together with gluon GFFs calculated in a light-front gluon-spectator model inspired by soft-wall AdS/QCD to predict both the differential and total cross sections for near-threshold <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mi>J</d:mi> <d:mo>/</d:mo> <d:mi mathvariant="normal">Ψ</d:mi> </d:math> and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi mathvariant="normal">ϒ</g:mi> </g:math> photoproduction. Our results for <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi>J</j:mi> <j:mo>/</j:mo> <j:mi>ψ</j:mi> </j:math> photoproduction show good agreement with the low-momentum-transfer data from the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:mrow> <l:mi>J</l:mi> <l:mo>/</l:mo> <l:mi>ψ</l:mi> <l:mtext>−</l:mtext> <l:mn>007</l:mn> </l:mrow> </l:math> experiment and the GlueX Collaboration at Jefferson Lab. However, at large momentum transfer, the next-to-leading order QCD effects are necessary to describe the data.