Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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   We discuss the impact of the new LHCb fixed-target $p\!+\!^{4}\!He$ data for
$D^0/{\bar D}^0$ production on the intrinsic $c \bar c$ component in the
nucleon wave function. Within the scenario presented here neither the
traditional gluon-gluon fusion or quark-antiquark annihilation mechanisms
calculated in the $k_T$-factorization approach nor their counterparts from the
collinear next-to-leading order collinear framework are sufficient to describe
the transverse momentum and rapidity distributions of $D^0/{\bar D}^0$ mesons.
First the $c{\bar c}$-pair production within the standard frameworks is
considered. Here a crucial role of the $c \to D$ hadronization effects at low
energies and low transverse momenta is found and discussed, which was not
analyzed in previous studies. A contribution related to intrinsic $c \bar c$
component in the nucleon wave function is included in addition. Two models of
the symmetric ($c(x) = \bar c(x)$) intrinsic charm (IC) component are
considered. The intrinsic charm $g^* c \to g c$ (or $g^* {\bar c} \to g {\bar
c}$) contribution needs to be regularized in order to obtain a suppression of
the minijet $p_{T}$ spectrum present in the phenomenological minijet model,
commonly used in Monte Carlo generators. We show that in our model the
regularization parameter can be obtained from the fit to the LHCb fixed-target
data under consideration here. We discuss uncertainties of our calculations
(scale, charm quark mass, fragmentation function) as well as set limits on the
IC probability. According to our model the intrinsic charm probability $P_{IC}
= 1.65\%$ allows to significantly improve description of the LHCb data but the
number is rather uncertain.

2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin