Holographic J / ψ 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/ψ off the proton using gauge/string duality and demonstrate that the t dependence of the differential cross section dσ/dt at small t is a sensitive probe of the trace anomaly.