It has been suggested that the production of a heavy quarkonium near threshold in electron-proton scattering can shed light on the origin of the proton mass via the QCD trace anomaly. We study the photoproduction of $J/\psi$ off the proton using gauge/string duality and demonstrate that the $t$ dependence of the differential cross section $d\sigma /dt$ at small $t$ is a sensitive probe of the trace anomaly.

• Received 27 August 2018

DOI:https://doi.org/10.1103/PhysRevD.98.074003

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Published by the American Physical Society