Pinning down the linearly-polarised gluons inside unpolarised protons using quarkonium-pair production at the LHC

Jean-Philippe Lansberg (1) , Cristian Pisano , Florent Scarpa (1) , Marc Schlegel

1 IPNO - Institut de Physique Nucléaire d'Orsay

We show that the production of J/ψ or ϒ pairs in unpolarised pp collisions is currently the best process to measure the momentum distribution of linearly-polarised gluons inside unpolarised protons through the study of azimuthal asymmetries. Not only the short-distance coefficients for such reactions induce the largest possible cos⁡4ϕ modulations, but analysed data are already available. Among the various final states previously studied in unpolarised pp collisions within the TMD approach, di- J/ψ production exhibits by far the largest asymmetries, in the region studied by the ATLAS and CMS experiments. In addition, we use the very recent LHCb data at 13 TeV to perform the first fit of the unpolarised transverse-momentum-dependent gluon distribution.

Mots clés: CERN LHC Coll; p p: scattering; Upsilon(9460): pair production; J/psi(3100): pair production; J/psi(3100): angular distribution; angular distribution: asymmetry; gluon: fusion; gluon: polarization; polarization: linear; gluon: transverse momentum; transverse momentum: factorization; transverse momentum: momentum spectrum; transverse momentum dependence

Domaines: Physique des Hautes Energies - Phénoménologie [hep-ph]; Physique des Hautes Energies - Expérience [hep-ex]; Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

Jean-Philippe Lansberg, Cristian Pisano, Florent Scarpa, Marc Schlegel. Pinning down the linearly-polarised gluons inside unpolarised protons using quarkonium-pair production at the LHC. Phys.Lett.B, 2018, 784, pp.217-222. ⟨10.1016/j.physletb.2018.08.004⟩. ⟨hal-01862028⟩