Exclusive $J/\psi$ production at the LHC in the $k_T$ factorization   approach
  The recent LHCb data for exclusive $J/\psi$ peripheral production at 13 TeV motivate an improved `NLO' analysis to estimate the gluon distribution at low $x$ in which we re-calculate the rapidity gap survival factors and use a more precise expression for the photon flux. We comment on the difference between the $k_T$ and collinear factorization approaches. 
S.P. Jones, A.D. Martin, M.G. Ryskin and T. Teubner
hep-ph