$J/\psi-007$ Experiment: A Threshold $J/\psi$ Photoproduction Measurement in Hall C at Jefferson Lab

We report on the Jefferson Lab experiment E12-16-007 ($J/\psi-007)$ where we made a measurement of the elastic doubly differential $J/\psi$ photo-production cross section as a function of proton momentum transfer $t$ and photon energy $E_{\gamma}$ in the region corresponding to the discovered charm pentaquark states reported by the LHCb collaboration. The experiment was performed using a high-intensity real photon beam generated by a 10.6 GeV incident electron beam traversing a copper radiator upstream of a liquid hydrogen target in Hall C. The two high momentum spectrometers of Hall C, HMS, and SHMS were used to detect in coincidence the $e^{+} e^{-}$ di-lepton $J/\psi$ decay pair. Both the $t$-channel and $s$-channel resonant $J/\psi$ production were explored using a high incident photon flux beam combined with spectrometers angular and momentum settings scanning a range from $t_{min}$ to large $t$, for every accessible photon energy above threshold. The sensitivity of the measurements to the $s$-channel resonant pentaquarks signals, if they exist, is maximal at large $t-t_{min}$. We will present preliminary results of the doubly differential $J/\psi$ cross-section measurement as well as the total photo-absorption cross-section.