Photoproduction of $J/\psi$ and $Upsilon$ states in exclusive and proton-dissociative diffractive events

Apr 13, 2016, 5:30 PM
SR2 (DESY Hamburg)


DESY Hamburg

Small-x, Diffraction and Vector Mesons WG4/WG5 joint session (HF+diffraction)


Dr Wolfgang Schafer (Institute of Nuclear Physics PAN)


The amplitude for $\gamma p \to V p$, where $V$ is a $J/\psi$ or $\Upsilon$ ground state or excited vector meson, is calculated in a pQCD $k_{T}$-factorization approach. We use this amplitude to predict the cross section for exclusive photoproduction of $J/\psi, psi', \Upsilon$ mesons in proton-proton collisions. Calculations are performed for a variety of unintegrated gluon distributions, and we compare to LHCb data. Here we especially focus on the possibilty of constraining saturation effects. Compared to earlier calculations we include both Dirac and Pauli electromagnetic form factors. We discuss the role of the $Q\bar Q$ light-cone wave functions for differential distributions for ratios such as $\sigma(\psi')/\sigma(J/\psi)$. Absorption effects are always taken into account. We also discuss the related diffractive production in proton dissociative events. Here special emphasis is put on electromagnetic dissociation , which is calculable without additional free parameters. Besides being of interest in their own right, dissociative events constitute an important experimental background to exclusive production. We also comment on the role of dissociative photoproduction for other states, e.g. light vector mesons. The talk will be based on A. Cisek, W. Scha\"fer and A. Szczurek, JHEP 1504 (2015) 159 and ongoing work by the same authors.

Primary authors

Dr Anna Cisek (University of Rzeszow) Prof. Antoni Szczurek (Institute of Nuclear Physics PAN) Dr Wolfgang Schafer (Institute of Nuclear Physics PAN)

Presentation materials