First Measurement of Near-Threshold J/ψ Exclusive Photoproduction off the Proton.

We report on the measurement of the γp→J/ψp cross section from E_{γ}=11.8  GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find that the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section dσ/dt has an exponential slope of 1.67±0.39  GeV^{-2} at 10.7 GeV average energy. The LHCb pentaquark candidates P_{c}^{+} can be produced in the s channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions B(P_{c}^{+}→J/ψp) and cross sections σ(γp→P_{c}^{+})×B(P_{c}^{+}→J/ψp).

G. Zhao | S. Cole | C. Kourkoumelis | S. Kuleshov | A. Somov | E. Anassontzis | C. Fanelli | L. Robison | Z. Papandreou | L. Pentchev | G. Kalicy | M. Patsyuk | J. Schwiening | G. Lolos | Z. Zhang | X. Shen | M. Baalouch | T. Britton | S. Fegan | K. Goetzen | B. Liu | F. Nerling | N. Qin | Q. Zhou | G. Vasileiadis | W. Boeglin | J. Reinhold | M. Williams | E. Chudakov | S. Dobbs | K. Seth | T. Xiao | M. Shepherd | L. Guo | T. Daniels | A. Dolgolenko | V. Lyubovitskij | J. Barlow | J. McIntyre | R. Pedroni | I. Strakovsky | R. Dzhygadlo | D. Ireland | J. Stevens | M. Dugger | B. Ritchie | N. Jarvis | W. Mcginley | C. Meyer | R. Schumacher | D. Sober | A. Barnes | R. Jones | F. Mokaya | E. Pooser | V. Crede | P. Eugenio | A. Ostrovidov | J. Frye | R. Miskimen | J. Hardin | S. Somov | C. Salgado | A. Gasparian | T. Black | L. Gan | G. Huber | H. Hakobyan | O. Soto | F. Barbosa | H. Egiyan | M. Ito | D. Lawrence | M. Mccaughan | E. Smith | S. Taylor | T. Whitlatch | B. Zihlmann | J. Foote | A. Teymurazyan | M. Mccracken | W. Briscoe | M. Boer | A. Deur | D. Werthmüller | A. Thiel | K. Livingston | I. Larin | V. Goryachev | V. Matveev | N. Cao | N. Gevorgyan | M. Dalton | D. Mack | A. Ali | T. Beattie | H. Marukyan | A. Ali | M. Amaryan | A. Austregesilo | E. Barriga | V. Berdnikov | W. Brooks | O. Cortes | R. Dotel | A. Ernst | A. Foda | S. Furletov | C. Gleason | A. Hamdi | A. Hurley | V. Kakoyan | M. Kamel | D. Lersch | H. Li | L. Ng | P. Pauli | K. Peters | D. Romanov | C. Romero | A. Schertz | K. Suresh | V. Tarasov | N. Wickramaarachchi | Y. Yang | J. Zarling | X. Zhou | R. Mitchell | I. Kuznetsov | W. Phelps | S. Han | V. Berdnikov | B. Cannon | V. Gauzshtein | A. Goncalves | W. Li | J. Stevens | M. McCaughan | R. Mitchell | R. Jones | M. McCracken | M. Ito | D. Mack | W. Brooks | A. Barnes | A. M. Foda | M. Williams | C. Meyer | M. Ito | V. Goryachev | R. T. Jones

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