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arXiv · 1905.10811

First measurement of near-threshold J/$\psi $ exclusive photoproduction off the proton

The GlueX Collaboration·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
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Abstract

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) $.

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The GlueX Collaboration, 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. 2019-05-26. First measurement of near-threshold J/$\psi $ exclusive photoproduction off the proton. https://doi.org/10.1103/physrevlett.123.072001

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