First Measurement of Near-Threshold $J/\psi$ Exclusive Photoproduction off the Proton
- Shepherd, Matthew
- 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, Ryan Edward
- 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.
DOIAbstract
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 that 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 $\mathscr{B}$($P_c+$ $\rightarrow$ $J/\psi$p) and cross sections $\sigma$($\gamma$p $\rightarrow$ $P_c+$) x $\...
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