Intrinsic charm in the nucleon and charm production at large rapidities in collinear, hybrid and kT-factorization approaches

Abstract

We discuss the role of intrinsic charm (IC) in the nucleon for forward production of c-quark (or $$ \overline{c} $$ c ¯ -antiquark) in proton-proton collisions for low and high energies. The calculations are performed in collinear-factorization approach with on-shell partons, kT-factorization approach with off-shell partons as well as in a hybrid approach using collinear charm distributions and unintegrated (transverse momentum dependent) gluon distributions. For the collinear-factorization approach we use matrix elements for both massless and massive charm quarks/antiquarks. The distributions in rapidity and transverse momentum of charm quark/antiquark are shown for a few different models of IC. Forward charm production is dominated by gc-fusion processes. The IC contribution dominates over the standard pQCD (extrinsic) gg-fusion mechanism of $$ c\overline{c} $$ c c ¯ -pair production at large rapidities or Feynman-xF. We perform similar calculations within leading-order and next-to-leading order kT-factorization approach. The kT-factorization approach leads to much larger cross sections than the LO collinear approach. At high energies and large rapidities of c-quark or $$ \overline{c} $$ c ¯ -antiquark one tests gluon distributions at extremely small x. The IC contribution has important consequences for high-energy neutrino production in the Ice-Cube experiment and can be, to some extent, tested at the LHC by the SHIP and FASER experiments by studies of the ντ neutrino production.

The Forward Physics Facility: Sites, Experiments, and Physics Potential

“…These constraints on the proton and nuclear structure will be fully complementary to those arising from other experiments operating at the same time, in particular from the EIC [268,275]. Existing calculations of the prompt neutrino flux at the FPF are also very uncertain [40,154,377]. Another approach to improve the calculations of the prompt neutrino flux will be the exploitation of the recently computed NNLO QCD corrections to heavy quark production [378,379], which will reduce the currently limiting theoretical uncertainty arising from missing higher-order uncertainties in both current FPF neutrino flux and prompt atmospheric neutrino flux predictions.…”

Intrinsic charm in the nucleon and forward production of charm: a new constrain from IceCube Neutrino Observatory

“…As discussed in Ref. [9], the cross section for charm production at large forward rapidities, which is the region of interest for estimating the prompt ν µ flux [3], can be expressed as…”

Impact of the LHCb $p\!+\!\!^{4}\!H\!e$ fixed-target $D^0/\bar{D^0}$ data on the intrinisic $c \bar c$ component in the nucleon

“…2) is obtained within the hybrid theoretical model discussed by us in detail in Ref. [6]. The LHCb 1 In the numerical calculations in Ref.…”

“…in Refs. [5,6]. Also here c(x) = c(x), but typical longitudinal momentum fractions of c-quark or c-antiquark are much smaller than in the Brodsky-Hoyer-Peterson-Sakai (BHPS) model.…”

“…In the present approach we are interested rather in production of c-quark and/or cantiquark and associated D mesons in the forward direction. Then gluon interaction in the target ( 4 He) (small-x) with c or c (large-x) in the incoming proton is the underlying partonic mechanism [6]. The 4 He is rather light nucleus and the associated nuclear effects are of the order of a few percent only and can be safely neglected.…”