Narrow Results

We study the associated $J∕\psi$ and direct photon production in the high-energy factorization, as it is formulated in the parton Reggeization approach, using two different models for the hadronization of a heavy quark–antiquark pair into a heavy quarkonium, namely the nonrelativistic quantum chromodynamics (NRQCD) and the improved color evaporation model (ICEM). We find essential differences in the predictions for cross-sections and transverse momenta spectra obtained using the NRQCD and the ICEM, which can be used to discriminate between these models. Our prediction for cross-sections of the associated $J∕\psi$ and direct photon production at the LHC energies slightly overestimates the results obtained earlier in the next-to-leading order (NLO) calculation in the collinear parton model (CPM). We predict different two-particle correlation spectra in the associated $J∕\psi$ and direct photon production, which may be of interest for experimental study.

Recent LHCb measurements of the $J/\psi$ meson production in jets are analyzed using fragmentation jet function formalism. It is shown that disagreement with theoretical predictions for distribution over the fraction of $J/\psi$ transverse momentum $z(J/\psi )$ in the cases of prompt production can be explained if one takes into account evolution of the fragmentation function and contributions from double parton scattering (DPS) mechanism or gluon fragmentation.

Extending a previous analysis¹ the double charmonium production and has been investigated with a data set of 155 fb^-1 with the Belle detector. Theoretical predictions for the cross section are one order of magnitude lower than the measured value and this discrepancy is still not understood. In a very recent update with a dataset of 285 fb^-1 strong evidence for a new charmonium state at a mass of 3.940 GeV was found.

In this work we study the process e⁺+e^-→J/Ψ+η_c at energy observed recently at B-factories whose measurements were made by Babar and Belle groups. We calculate the cross-section for this process in the Bethe–Salpeter formalism under Covariant Instantaneous Anstaz. To simplify our calculation, the heavy quark approximation is employed in the quark and gluon propagators. In the exclusive process of e⁺e^- annihilation into two heavy quarkonia, the cross-section calculated in this scenario is compatible with the experimental data of Babar and Belle.