Double Prompt $J/\psi$ Hadroproduction in the Parton Reggeization Approach with High-Energy Resummation

We study double prompt $J/\psi$ hadroproduction within the nonrelativistic-QCD factorization formalism adopting the parton Reggeization approach to treat initial-state radiation in a gauge invariant and infrared-safe way. We present first predictions for the cross section distributions in the transverse momenta of the subleading $J/\psi$ meson and the $J/\psi$ pair. Already at leading order in ${\alpha }_s$, these predictions as well as those for the total cross section and its distributions in the invariant mass $m_{\psi \psi }$ and the rapidity separation $|Y|$ of the $J/\psi$ pair nicely agree with recent ATLAS and CMS Collaboration measurements, except for the large-$m_{\psi \psi }$ and $\mathrm{large}\text{−}|Y|$ regions, where the predictions substantially undershoot the data. In the latter regions, Balitsky-Fadin-Kuraev-Lipatov resummation is shown to enhance the cross sections by up to a factor of 2 and so to improve the description of the data.

Figure 1

Typical Feynman diagrams for $R^{+}{R}^{-}\to c\overline{c}(m)c\overline{c}(n)$ of types (a) non-$t$ channel gluon exchange and $t$ channel gluon exchange at (b) LO, (c) NLO, and (d) NNLO in ${\alpha }_s$.

Figure 2

The (a) $p_T^{\psi \psi }$, (b) $m_{\psi \psi }$, and (c) $|Y|$ distributions of double prompt $J/\psi$ production measured by the CMS Collaboration [10] are compared to our LO NRQCD predictions in the PRA without (dashed lines) and with BFKL resummation (solid lines) including their scale uncertainties (yellow and blue bands). Adding the total ${\mathrm{NLO}}^{*}$ NLT contributions on top of the central LO NRQCD predictions in the PRA with BFKL resummation yields the red solid lines. Frame (a) also contains the evaluations with the UPDF sets of Refs. [28, 32] (B-MSTW, dotted lines) and Ref. [33] (JS-HJ, dot-dashed lines).

Figure 3

As in Fig. 2, but for the $p_{2T}$ (left column), $p_T^{\psi \psi }$ (middle column), and $m_{\psi \psi }$ (right column) distributions measured by the ATLAS Collaboration [11] in regions I (upper row) and II (lower row).

Figure 4

Schematic representation of Eq. (2).