Probing the transverse dynamics and polarization of gluons inside the proton at the LHC

Transverse momentum dependent gluon distributions encode fundamental information on the structure of the proton. Here we show how they can be accessed in heavy quarkonium production in proton-proton collisions at the LHC. In particular, their first determination could come from the study of an isolated J/psi or Upsilon particle, produced back to back with a photon.