Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>J</mml:mi></mml:math>/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>ψ</mml:mi></mml:math> photoproduction cross section over the full near-threshold kinematic region
S. Adhikari, F. Afzal, C. S. Akondi, M. Albrecht, M. J. Amaryan, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, Fernando Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, В. В. Бердников, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, Danae Byer, E. Chudakov, P. L. Cole, O. Cortes, V. Credé, M. M. Dalton, D. Darulis, A. Deur, S. Dobbs, A. Dolgolenko, R. Dotel, M. Dugger, R. Dzhygadlo, D. Ebersole, H. Egiyan, T. Erbora, P. Eugenio, A. Fabrizi, C. Fanelli, S. Fang, S. Fegan, J. Fitches, A. M. Foda, S. Furletov, L. Gan, He Gao, A. Gardner, A. Gasparian, C. Gleason, K. Goetzen, V. Goryachev, B. Grube, J. Guo, L. Guo, T. J. Hague, H. Hakobyan, J. Hernandez, Nathaniel Hoffman, D. Hornidge, G. Hou, G. M. Huber, P. Hurck, A. Hurley, W. Imoehl, D. G. Ireland, M. M. Ito, I. Jaeglé, N. S. Jarvis, T. Jeske, R. T. Jones, V. Kakoyan, G. Kalicy, V. Khachatryan, M. Khatchatryan, C. Kourkoumelis, A. LaDuke, I. Larin, David Lawrence, D. I. Lersch, H. Li, W. B. Li, B. Liu, K. Livingston, G. J. Lolos, L. Lorenti, Valery E. Lyubovitskij, D. Mack, A. Mahmood, P. P. Martel, H. Marukyan, V. Matveev, M. McCaughan, M. McCracken, C. A. Meyer, R. Miskimen, R. E. Mitchell, K. Mizutani, V. Neelamana, L. Ng, E. Nissen
Abstract
New results from the GlueX experiment provide improved cross sections for the photoproduction from the proton of $J/\ensuremath{\psi}$ mesons via the $\ensuremath{\gamma}+p\ensuremath{\rightarrow}J/\ensuremath{\psi}+p$ reaction. Such mesons have charm/anti-charm heavy-quark content. Measurements of this reaction near the kinematic threshold can help constrain aspects of the density distribution of gluons in the proton and how they contribute to the proton mass, under the assumption that $J/\ensuremath{\psi}$ production proceeds primarily through the exchange of gluons with the proton. However, these new measurements suggest contributions in addition to gluon exchange, pointing to the need for further theoretical work and more precise experimental measurements.