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

• DOI: 10.1103/physrevlett.123.072001
• Publication Date: 2019-08-14T15:28:28Z
• Authors: A. Ali; M. Amaryan; E. G. Anassontzis; A. Austregesilo; M. Baalouch; F. Barbosa; J. Barlow; A. Barnes; E. Barriga; T. D. Beattie; V. V. Berdnikov; T. Black; W. Boeglin; M. Boer; W. J. Briscoe; T. Britton; W. K. Brooks; B. E. Cannon; N. Cao; E. Chudakov; S. Cole; O. Cortes; V. Crede; M. M. Dalton; T. Daniels; A. Deur; S. Dobbs; A. Dolgolenko; R. Dotel; M. Dugger; R. Dzhygadlo; H. Egiyan; A. Ernst; P. Eugenio; C. Fanelli; S. Fegan; A. M. Foda; J. Foote; J. Frye; S. Furletov; L. Gan; A. Gasparian; V. Gauzshtein; N. Gevorgyan; C. Gleason; K. Goetzen; A. Goncalves; V. S. Goryachev; L. Guo; H. Hakobyan; A. Hamdi; S. Han; J. Hardin; G. M. Huber; A. Hurley; D. G. Ireland; M. M. Ito; N. S. Jarvis; R. T. Jones; V. Kakoyan; G. Kalicy; M. Kamel; C. Kourkoumelis; S. Kuleshov; I. Kuznetsov; I. Larin; D. Lawrence; D. I. Lersch; H. Li; W. Li; B. Liu; K. Livingston; G. J. Lolos; V. Lyubovitskij; D. Mack; H. Marukyan; V. Matveev; M. McCaughan; M. McCracken; W. McGinley; J. McIntyre; C. A. Meyer; R. Miskimen; R. E. Mitchell; F. Mokaya; F. Nerling; L. Ng; A. I. Ostrovidov; Z. Papandreou; M. Patsyuk; P. Pauli; R. Pedroni; L. Pentchev; K. J. Peters; W. Phelps; E. Pooser; N. Qin; J. Reinhold; B. G. Ritchie; L. Robison; D. Romanov; C. Romero; C. Salgado; A. M. Schertz; R. A. Schumacher; J. Schwiening; K. K. Seth; X. Shen; M. R. Shepherd; E. S. Smith; D. I. Sober; A. Somov; S. Somov; O. Soto; J. R. Stevens; I. I. Strakovsky; K. Suresh; V. Tarasov; S. Taylor; A. Teymurazyan; A. Thiel; G. Vasileiadis; D. Werthmüller; T. Whitlatch; N. Wickramaarachchi; M. Williams; T. Xiao; Y. Yang; J. Zarling; Z. Zhang; G. Zhao; Q. Zhou; X. Zhou; B. Zihlmann
• Keywords: Particles and fields; Quarkonia; Nuclear physics; FOS: Physical sciences; 7. Clean energy; 01 natural sciences; Elementary Particles and Fields and String Theory; 0103 physical sciences; Photon and charged lepton interactions with hadrons; Exotic baryons; Nuclear; Nuclear Experiment (nucl-ex); Nuclear Experiment

We report on the measurement of the $��p \rightarrow J/��p$ cross section from $E_��= 11.8$ 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 $d��/dt$ 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 $\mathcal{B}(P_c^+ \rightarrow J/��p)$ and cross sections $��(��p \to P_c^+)\times\mathcal{B}(P_c^+ \to J/��p) $.<br/>12 pages, 7 figures<br/>