Holographic $J/\psi$ production near threshold and the proton mass problem

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.