Abstract
We study double prompt J/ψ 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/ψ meson and the J/ψ pair. Already at leading order in α_{s}, these predictions as well as those for the total cross section and its distributions in the invariant mass m_{ψψ} and the rapidity separation |Y| of the J/ψ pair nicely agree with recent ATLAS and CMS Collaboration measurements, except for the large-m_{ψψ} and large-|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.
Highlights
Despite concerted experimental and theoretical endeavors ever since the discovery of the J=ψ meson more than four decades ago, its production mechanism has remained mysterious; for a recent review, see Ref. [1]
We study double prompt J=ψ hadroproduction within the nonrelativistic-QCD factorization formalism adopting the parton Reggeization approach to treat initial-state radiation in a gauge invariant and infraredsafe way
The factorization approach [2] to nonrelativistic QCD (NRQCD) [3] endowed with velocity scaling rules [4] for the longdistance matrix elements (LDMEs), which is by far the most acceptable candidate theory for heavy-quarkonium production and decay and has been elaborated at next-toleading order (NLO), has been challenged by the longstanding J=ψ polarization puzzle [5] and by the inadequate description of ηc hadroproduction data with J=ψ LDMEs converted via heavy-quark spin symmetry [6]
Summary
Despite concerted experimental and theoretical endeavors ever since the discovery of the J=ψ meson more than four decades ago, its production mechanism has remained mysterious; for a recent review, see Ref. [1]. These single-parton scattering (SPS) predictions only amount to a few percent of the CMS data in the regions of large invariant mass mψψ or rapidity separation jYj 1⁄4 jy1 − y2j of the J=ψ pair, the color-octet contributions, in particular those involving t channel gluon exchanges, enhance the QCD-corrected [15] color-singlet contribution of gg → 2ccð3S1⁄211Þ there by more than 1 order of magnitude.
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