Prompt $$\eta _c$$ meson production at the LHC in the NRQCD with $$k_T$$-factorization

Abstract

In the framework of the kT -factorization approach, the prompt production of ηc mesons at the LHC conditions is studied. Our consideration is based on the off-shell amplitudes for hard partonic subprocesses and on the nonrelativistic QCD (NRQCD) formalism for the formation of bound states. We try two latest parametrizations for noncollinear, or transverse momentum dependent (TMD) gluon densities derived from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) equation. We use the values of the nonperturbative matrix elements obtained from a combined fit of the ηc and J/ψ differential cross sections. Finally, we show an universal set of parameters that provides a reasonable simultaneous description for all of the available data on the prompt J/ψ and ηc production at the LHC.

Prompt hadroproduction of ηc(1S, 2S) in the kT-factorization approach

“…We insist that our choice is consistent with the Feynman rules derived for reggeized off-shell gluons [10,11]. We have checked, that with the expression used in [25], our results in the LHCb kinematics would decrease by ≈ 20 − 30%.…”

“…See the recent ref. [25] for an estimate which finds a few percent contribution from the feed down. We also do not include a possible color-octet contribution.…”

“…Finally, let us comment that some versions of k T -factorization, e.g. [25], use a different formula for calculation of the inclusive cross section from UGD and off-shell matrix element, replacing the "flux-factor" F = 2x 1 x 2 s in eq. (2.1) by a different expression with the same on-shell limit.…”

“…Previously, the prompt η c (1S) production was discussed in various factorization approaches: collinear factorization [18][19][20][21][22], the TMD-factorization with transverse momentum dependent distributions of on-shell gluons, and on-shell matrix elements [23,24], and the k T -factorization in ref. [25]. So far, the η c (2S) production process was discussed only in the collinear factorization approach in ref.…”

ϒ(3S) and χb(3P) production and polarization in the NRQCD with kT–factorization

“…A possible solution to the "polarization puzzle" has been proposed recently in the framework of a model that interprets the soft final state gluon radiation as a series of color-electric dipole transitions [10]. It was already used for the prompt charmonia production [11]. In this approach, a soft gluon with a small energy E ∼ Λ QCD is emitted after the hard interaction is over, bringing away the unwanted color and changing other quantum numbers of the produced CO system.…”