First Measurement of Near-Threshold $J/\psi$ Exclusive Photoproduction off the Proton

Journal Article · 12 August 2019 · Physical Review Letters

DOI: https://doi.org/10.1103/PhysRevLett.123.072001 · OSTI ID:1574399

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

We report on the measurement of the $$\gamma p \rightarrow J/\psi p$$ cross section from $$E_\gamma = 11.8$$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $$d\sigma /dt$$ has an exponential slope of $$1.67 \pm 0.39$$ 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 $$\mathcal{B}(P_c^+ \rightarrow J/\psi p)$$ and cross sections $$\sigma(\gamma p \to P_c^+)\times\mathcal{B}(P_c^+ \to J/\psi p) $$.

• Research Organization: George Washington Univ., Washington, DC (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: German Research Foundation (DFG); National Natural Science Foundation of China; National Science Foundation (NSF); Natural Sciences and Engineering Research Council of Canada; Russian Foundation for Basic Research; UK Science and Technology Facilities Council; USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
• Contributing Organization: GlueX Collaboration
• Grant/Contract Number: AC05-06OR23177; SC0016583
• OSTI ID: 1574399
• Report Number(s): DOE/OR/23177--4686; JLAB-PHY--19-2946; arXiv:1905.10811
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 7 Vol. 123; ISSN 0031-9007; ISSN PRLTAO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English