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

Journal
Physical Review Letters
Date Issued
2019-08-13
Author(s)
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.
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.
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.
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.
DOI
Abstract
We report on the measurement of the 𝛾⁒𝑝→𝐽/πœ“β’π‘ cross section from 𝐸𝛾=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 π‘‘β’πœŽ/𝑑⁒𝑑 has an exponential slope of 1.67Β±0.39  GeVβˆ’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/πœ“β’π‘) and cross sections 𝜎⁑(𝛾⁒𝑝→𝑃+
𝑐)×ℬ⁑(𝑃+
𝑐→𝐽/πœ“β’π‘).
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