Narrow Results

We perform a comparison of the impact of different intrinsic charm (IC) models, based on the prediction of the differential cross-sections of $Z$-boson and $c$-jet production in $pp$ collision. It is shown that regardless of choosing the model, considering nonperturbative intrinsic charm component increases the magnitude of the cross-section when the $Z$ transverse momentum grows or at large rapidity $(y)$ of the $Z$. Moreover, to evaluate the effect of different parton distribution functions (PDFs), we also compare the results of two PDF sets in prediction of production $Z+c$-jet in $pp$ at a center-of-mass energy of 13 TeV with taking into account the intrinsic charm contribution in the proton. It is shown that the various PDF sets give some difference in the description of the $Z+c$-jet cross-section.

During the past 40 years, the production of pairs of $J∕\psi$ mesons in high-energy hadron collisions has been studied by several experiments. Despite the experimental and theoretical efforts, the origin of the process and the relative weight of different production mechanisms remain unknown. Depending on the energy scale, the double $J∕\psi$ production can be described by single- and/or double-parton scattering sub-processes and gluon–gluon fusion or quark–antiquark annihilation mechanisms. The process can also be related to the hypothesis of the intrinsic charm of hadrons and the existence of exotic tetraquark states which were predicted by various theoretical models and have recently been observed by the LHCb experiment.

To study dimuon pair production, the COMPASS experiment at CERN uses a 190GeV/$c$ negative pion beam impinging on different nuclear targets. First preliminary COMPASS results on $J∕\psi$ pair production will be presented. The search for possible signals from exotic resonances and the study of double $J∕\psi$ production mechanisms will be discussed.