We investigate the possibility to constrain the intrinsic charm probability
w
c
c
¯
=
P
c
c
¯
/
p
using first ATLAS data on the associated production of prompt photons and charm-quark jets in
pp
...collisions at
s
=
8
TeV. The upper limit
w
c
c
¯
<
1.93
% is obtained at the 68 % confidence level. This constraint is primarily determined from the theoretical scale and systematical experimental uncertainties. Suggestions for reducing these uncertainties are discussed. The implications of intrinsic heavy quarks in the proton for future studies at the LHC are also discussed.
Transverse momentum dependent (TMD) parton distributions in a proton are important in high-energy physics from both theoretical and phenomenological points of view. Using the latest RHIC and LHC data ...on the inclusive soft hadron production in pp and AA collisions at small transverse momenta, we determine the parameters of the initial TMD gluon density derived in the framework of a quark-gluon string model at the low scale μ0∼1–2 GeV and refine its large-x behavior using the LHC data on the tt¯ production at s=13 TeV. Then, we apply the Catani-Ciafaloni-Fiorani-Marchesini evolution equation to extend the obtained TMD gluon density to the whole kinematical region. In addition, the complementary TMD valence and sea quark distributions are generated. The latter are evaluated in the approximation where the gluon-to-quark splitting occurs at the last evolution step using the TMD gluon-to-quark splitting function. Several phenomenological applications of the proposed TMD quark and gluon densities to the LHC processes are discussed.
Novel heavy-quark physics phenomena Brodsky, S.J.; Lykasov, G.I.; Lipatov, A.V. ...
Progress in particle and nuclear physics,
September 2020, 2020-09-00, 2020-09-01, Letnik:
114, Številka:
C
Journal Article
Recenzirano
Odprti dostop
We review the current understanding of heavy quark parton distributions in nucleons and their impact on deep inelastic scattering, collider physics, and other processes at high energies. The ...determination of the heavy-quark parton distribution functions is particularly significant for the analysis of hard processes at LHC energies, including the forward rapidity high xF domain. The contribution of “intrinsic” heavy quarks, which are multiply connected to the valence quarks of nucleons, is reviewed within non-perturbative physics which provides new information on the fundamental structure of hadrons in QCD. A new prediction for the non-perturbative intrinsic charm–anticharm asymmetry of the proton eigenstate has recently been obtained from a QCD lattice gauge theory calculation of the proton’s GEp(Q2) form factor (Sufian et al., 2020). This form factor only arises from non-valence quarks and anti-quarks if they have different contributions in the proton’s eigenstate. This result, together with the exclusive and inclusive connection and analytic constraints on the form of hadronic structure functions from Light-Front Holographic QCD (LFHQCD) predicts a significant non-perturbative c(x,Q)−c̄(x,Q) asymmetry in the proton structure function at high x, consistent with the dynamics predicted by intrinsic charm models. Recent ATLAS data on the associated production of prompt photons and charm-quark jets in pp collisions at s=8TeV has provided new constraints on non-perturbative intrinsic charm and tests of the LGTH predictions. We also focus on other experimental observables which have high sensitivity to the intrinsic heavy contributions to PDFs.
We consider an observable very sensitive to the nonzero intrinsic charm (IC) contribution to the proton density. It is the ratio between the differential cross sections of the photon or Z-boson and ...c-jet production in the pp collision, γ(Z)+c, and the γ(Z) and the b-jet production. It is shown that this ratio can be approximately flat or increasing at large γ(Z) transverse momenta pT, and their pseudorapidities 1.5<η<2.4 if the IC contribution is taken into account. On the contrary, in the absence of the IC, this ratio decreases as pT grows. We also present the ratios of the cross sections integrated over pT as a function of the IC probability w. It is shown that these ratios are mostly independent on the theoretical uncertainties, and such predictions could therefore be much more promising for the search for the intrinsic charm signal at the LHC compared to the predictions for pT spectra, which significantly depend on these uncertainties.
The cross section of associated production of a Z boson with heavy flavor jets in pp collisions is calculated using the Sherpa Monte Carlo generator and the analytical combined QCD approach based on ...kT factorization at small x and conventional collinear QCD at large x. A satisfactory description of the ATLAS and CMS data on the pT spectra of Z bosons and c jets in the whole rapidity, y, region is shown. Searching for the intrinsic charm (IC) contribution in these processes, which could be visible at large y>1.5, we study observables very sensitive to nonzero IC contributions and less affected by theoretical QCD scale uncertainties. One of such observables is the so-called double ratio, the ratio of the differential cross section of Z+c production in the central region of |y|<1.5 and in the forward region 1.5<|y|<2.5, divided by the same ratio for Z+b production. These observables could be more promising for the search of IC at LHC as compared to the observables considered earlier.
A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and ...uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.
The calculation of inclusive spectra of pions produced in
pp
and
AA
collisions as functions of the rapidity
y
is presented within the self-similarity approach. It is shown that at not too large ...rapidities
y
one can obtain an analytical form of the self-similarity function
Π
(
y
,
p
t
)
dependent on
y
and on the hadron transverse momentum
p
t
. A satisfactory description of the data on rapidity spectra at
|
y
|
≤
0.3 is presented within the approach applied. The energy dependence of these spectra is also shown to be universal.
.
The self-consistent approach based on the similarity of inclusive spectra of hadrons produced in
pp
and
AA
collisions is reviewed. We suggest its modification due to the quark-gluon dynamics to ...describe the inclusive spectra of hadrons produced in
pp
collision as a function of the transverse momentum
p
t
at mid-rapidity. The extension of this approach to analyze the pion
p
t
-spectra produced in
AA
collision at high and middle energies and mid-rapidity is given. The satisfactory description of experimental data on these spectra in
pp
and
AA
collisions within the offered approach is shown.
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