Intrinsic charm in the nucleon and charm production at large rapidities in collinear, hybrid and k T -factorization appr
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Springer
Received: July Revised: September Accepted: September Published: October
13, 15, 21, 21,
2020 2020 2020 2020
Rafal Maciula and Antoni Szczurek1 Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, PL-31-342 Krak´ ow, Poland
E-mail: [email protected], [email protected] Abstract: We discuss the role of intrinsic charm (IC) in the nucleon for forward production of c-quark (or 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¯ 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 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. Keywords: QCD Phenomenology ArXiv ePrint: 2006.16021 1
Also at University of Rzesz´ ow, PL-35-959 Rzesz´ ow, Poland.
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP10(2020)135
JHEP10(2020)135
Intrinsic charm in the nucleon and charm production at large rapidities in collinear, hybrid and kT -factorization approaches
Contents 1 Introduction
1
2 Models of intrinsic charm in a nucleon
2 4 4 7 9 9 10
4 Results 4.1 The collinear approach 4.2 The hybrid model 4.3 The kT -factorization approach 4.4 Predictions for future experiments
11 11 14 16 18
5 Conclusions
20
1
Introduction
The text-book proton consists of uud valence quarks. This picture is by far too simplified. In fact there is strong evidence for internal strangeness and somewhat smaller for internal charm content of the nonperturbative proton. Different pictures of nonperturbative c¯ c content were proposed in the past. A first example is relatively old BHPS model [1] which assumes uudc¯ c 5-parton Fock configurations (see also refs. [2, 3]). Another picture ¯ 0 Λc or proposed in the literature is a meson cloud model (MCM) [4–8], where the p → D DΣc fluctuations of the proton are considered. While in the first model c(x) = c¯(x) in the MCM c(x) 6= c¯(x). The m
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