Linearly polarized gluon density in the rescaling model
The low-x behavior of the linearly polarized gluon density h_{g}(x,k_t^2, Q^2) in nuclei is studied in the rescaling model at small transverse momentum k_t.
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arXiv subjects
N. A. Abdulov
Publications and source records attributed to N. A. Abdulov.
Linearly polarized gluon density at low x
Based on a solution of DGLAP evolution equations at small values of Bjorken variable x, a simple analytic approximation for so-called linearly polarized gluon density \tilde{h}_1^{\perp g}(x,k_t^2, Q^2) is obtained at LO of perturbation theory.
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On x-independence of RQ = FLQ/F2Q ratio at low x
We give predictions for the ratio RQ(x,Q2)=FLQ(x,Q2)/F2Q(x,Q2) at small values of Bjorken variable x in the first three orders of perturbation theory. We show an approximate x-independence of RQ(x,Q2) at low x and non-large Q2 values (Q2 < 8--10 m2Q), irrespectively on the gluon density in a proton used in the calculations. This observation could be useful in subsequent phenomenological studies of the heavy flavor production at future lepton-hadron and hadron-hadron colliders.
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Gluon density in the rescaling model
The behavior of the gluon density in nuclei is investigated in the framework of the rescaling model.
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Parametrizations of collinear and k_T-dependent parton densities in a proton
A new type of parametrization for parton distribution functions in a proton, based on their $Q^2$-evolution at large and small $x$ values, is constructed. In our analysis, the valence and nonsinglet parts obey the Gross-Llewellyn-Smith and Gottfried sum rules, respectively. For the singlet quark and gluon densities momentum conservation is taken into account. Then, using the Kimber-Martin-Ryskin prescription, we extend the consideration to Transverse Momentum Dependent (TMD, or unintegrated) gluon and quark distributions in a proton, which currently plays an important role in a number of phenomenological applications. The analytical expressions for the latter, valid for both low and large $x$, are derived for the first time.
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Bottomonium production and polarization in the NRQCD with $k_T$-factorization. III: $Υ(1S)$ and $χ_b(1P)$ mesons
The $Υ(1S)$ meson production and polarization at high energies is studied in the framework of the $k_T$-factorization approach. Our consideration is based on the non-relativistic QCD formalism for a bound states formation and off-shell production amplitudes for hard partonic subprocesses. The direct production mechanism, feed-down contributions from radiative $χ_b(mP)$ decays and contributions from $Υ(3S)$ and $Υ(2S)$ decays are taken into account. The transverse momentum dependent (TMD) gluon densities in a proton were derived from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation and the Kimber-Martin-Ryskin prescription. Treating the non-perturbative color octet transitions in terms of multipole radiation theory, we extract the corresponding non-perturbative matrix elements for $Υ(1S)$ and $χ_b(1P)$ mesons from a combined fit to transverse momenta distributions measured at various LHC experiments. Then we apply the extracted values to investigate the polarization parameters $λ_θ$, $λ_ϕ$ and $λ_{θϕ}$, which determine the $Υ(1S)$ spin density matrix. Our predictions have a reasonably good agreement with the currently available Tevatron and LHC data within the theoretical and experimental uncertainties.
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TMDlib2 and TMDplotter: a platform for 3D hadron structure studies
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.
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Bottomonia production and polarization in the NRQCD with $k_T$-factorization. II: $Υ(2S)$ and $χ_b(2P)$ mesons
The $Υ(2S)$ production and polarization at high energies is studied in the framework of $k_T$-factorization approach. Our consideration is based on the non-relativistic QCD formalism for bound states formation and off-shell production amplitudes for hard partonic subprocesses. The direct production mechanism, feed-down contributions from radiative $χ_b(3P)$ and $χ_b(2P)$ decays and contributions from $Υ(3S)$ decays are taken into account. The transverse momentum dependent gluon densities in a proton were derived from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation as well as from the Kimber-Martin-Ryskin prescription. Treating the non-perturbative color octet transitions in terms of the mulitpole radiation theory, we extract the corresponding non-perturbative matrix elements for $Υ(2S)$ and $χ_b(2P)$ mesons from a combined fit to $Υ(2S)$ transverse momenta distributions measured by the CMS and ATLAS Collaborations at the LHC energies $\sqrt s = 7$ and $13$ TeV and from the relative production rate $R^{χ_b(2P)}_{Υ(2S)}$ measured by the LHCb Collaboration at $\sqrt s = 7$ and $8$ TeV. Then we apply the extracted values to investigate the polarization parameters $λ_θ$, $λ_ϕ$ and $λ_{θϕ}$, which determine the $Υ(2S)$ spin density matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties.
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Bottomonia production and polarization in the NRQCD with $k_T$-factorization. I: $Υ(3S)$ and $χ_b(3P)$ mesons
The $Υ(3S)$ production and polarization at high energies is studied in the framework of $k_T$-factorization approach. Our consideration is based on the non-relativistic QCD formalism for bound states formation and off-shell production amplitudes for hard partonic subprocesses. The transverse momentum dependent (TMD, or unintegrated) gluon densities in a proton were derived from the Ciafaloni-Catani-Fiorani-Marchesini (CCFM) evolution equation as well as from the Kimber-Martin-Ryskin (KMR) prescription. Treating the non-perturbative color octet transitions in terms of the multipole radiation theory and taking into account feed-down contributions from radiative $χ_b(3P)$ decays, we extract the corresponding non-perturbative matrix elements for $Υ(3S)$ and $χ_b(3P)$ mesons from a combined fit to $Υ(3S)$ transverse momenta distributions measured by the CMS and ATLAS Collaborations at the~LHC energies $\sqrt s = 7$ and $13$~TeV and central rapidities. Then we apply the extracted values to describe the CDF and LHCb data on $Υ(3S)$ production and to investigate the polarization parameters $λ_θ$, $λ_ϕ$ and $λ_{θϕ}$, %and $\tildeλ$, which determine the $Υ(3S)$ spin density matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties.
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Employing RHIC and LHC data to determine TMD gluon density in a proton
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 quark-gluon string model at the low scale $μ_0 \sim 1 - 2$ GeV and refine its large-$x$ behaviour using the LHC data on the $t \bar t$ production at $\sqrt s = 13$ TeV. Then, we apply the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) 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.
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Inclusive Higgs boson production at the LHC in the kt-factorization approach
We investigate the inclusive Higgs boson production in proton-proton collisions at the CERN LHC conditions using the $k_T$-factorization approach. Our analysis is based on the dominant off-shell gluon-gluon fusion subprocess (where the transverse momenta of initial gluons are taken into account) and covers $H \to γγ$, $H \to ZZ^* \to 4l$ (where $l = e,μ$) and $H \to W^+ W^- \to e^\pm μ^\mp ν\bar ν$ decay channels. The transverse momentum dependent (or unintegrated) gluon densities in a proton were derived from Ciafaloni-Catani-Fiorani-Marchesini equation or, alternatively, were chosen in accordance with Kimber-Martin-Ryskin prescription. We estimate the theoretical uncertainties of our calculations and compare our results with next-to-next-to-leading-order plus next-to-next-to-leading-logarithmic ones obtained using collinear QCD factorization. Our predictions agree well with the latest experimental data taken by the CMS and ATLAS Collaborations at $\sqrt s = 8$ and $13$~TeV.
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