Search for Sub-threshold Photoproduction of J/Psi Mesons
  A search was made for sub-threshold $J/\psi$ production from a carbon target using a mixed real and quasi-real Bremsstrahlung photon beam with an endpoint energy of 5.76 GeV. No events were observed, which is consistent with predictions assuming quasi-free production. The results place limits on exotic mechanisms that strongly enhance quasi-free production. 
P. Bosted, J. Dunne, C. A. Lee, P. Junnarkar, J. Arrington, R.   Asaturyan, F. Benmokhtar, M.E. Christy, E. Chudakov, B. Cla...