Topics in associated $J/\psi +c+\overline{c}$ production at modern colliders

In the framework of perturbative QCD and nonrelativistic bound state formalism, we calculate the production of $J/\psi$ mesons associated with open-charm particles at HERA and Tevatron conditions. We show that the contribution from $J/\psi +c+\overline{c}$ channel becomes comparable with that of $J/\psi$ sole production at high $J/\psi$ transverse momenta (approximately, at $p_{\psi ,T}>10\mathrm{GeV}$). We investigate the $J/\psi$ polarization effects and kinematic correlations between $J/\psi$ mesons and the accompanying open-charmed mesons. We show that the correlations are sensitive to the initial $k_t$ of the colliding partons, and so, can be considered as an additional test discriminating the collinear parton model and the $k_t$-factorization approach.

Figure 1

Feynman diagrams representing the subprocess $g+g\to J/\psi +c+\overline{c}$.

Figure 2

Diagrams representing $J/\psi$ production subprocesses. (a) Leading-order gluon-gluon fusion. (b) Color-octet scheme. Part of the diagram to the right of the dashed line is treated in a nonperturbative way: the emission of soft gluons is absorbed into phenomenological color-octet matrix elements. (c) Higher-order contributions connected with initial gluon radiation. In the $k_t$-factorization approach, the upper and the lower parts of this diagram are included in the $k_T$ evolution of gluon densities.

Figure 3

$J/\psi +c+\overline{c}$ production at the Tevatron. Upper panel: $J/\psi$ transverse momentum distribution; middle panel: charmed meson transverse momentum distribution; lower panel: the ratio of the $J/\psi +c+\overline{c}$ production cross section to the noncharm-associated $J/\psi$ production. Solid histograms: predictions of the collinear parton model; dashed and dash-dotted histograms: $k_t$-factorization approach with JB [12] and dGRV [3] gluon densities, respectively.

Figure 4

$J/\psi +c+\overline{c}$ production at the Tevatron. $J/\psi$ and charmed meson rapidity distributions. Notation of the curves is as in Fig. 3.

Figure 5

$J/\psi +c+\overline{c}$ production at the Tevatron. Kinematic correlations between the $J/\psi$ and accompanying charmed mesons. Upper panel: azimuthal angle difference; middle panel, pseudorapidity difference; lower panel: combined variable $\Delta R=\sqrt{(\Delta \phi {)}^2-(\Delta \eta {)}^2}$. Notation of the curves is as in Fig. 3.

Figure 6

$J/\psi +c+\overline{c}$ production at the Tevatron. The fraction of longitudinally polarized $J/\psi$ mesons as a function of $J/\psi$ transverse momentum, $J/\psi$ rapidity, $J/\psi -D$ azimuthal angle difference, and $J/\psi -D$ pseudorapidity difference, from top to bottom, respectively. Notation of the curves is as in Fig. 3.

Figure 7

$J/\psi +c+\overline{c}$ production at HERA. Upper panel: $J/\psi$ transverse momentum distribution; middle panel, charmed meson transverse momentum distribution; lower panel: the ratio of the $J/\psi +c+\overline{c}$ production cross section to the noncharm-associated $J/\psi$ production. Solid histograms: predictions of the collinear parton model; dashed histograms: $k_t$-factorization approach with JB [12] gluon densities.

Figure 8

$J/\psi +c+\overline{c}$ production at HERA. $J/\psi$ and charmed meson rapidity distributions. Positive direction corresponds to the proton beam. Notation of the curves is as in Fig. 7.