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G. I. Lykasov

Publications and source records attributed to G. I. Lykasov.

At least 19 recordsLinked to original sources
arXiv2026

Isospin-symmetry in $pp$ and $AA$ collisions

The hypothesis of a violation of isospin-symmetry in pp and AA collisions is discussed. We show that the ratio of charged-to-neutral kaon cross sections, $R_K~=~\frac{σ_{K^+}+σ_{K^-}}{2σ_{K^0_S}}$, calculated within the similarity approach, including the gluon transverse momentum dependence (TMD) at low QCD scales, and using the Lund model in the form of the MC generator PYTHIA, is above 1 at energies $\sqrt{s}$ up to 20 GeV, even in the case of isospin-symmetry conservation. It decreases to 1, when the energy rises to a few TeV (ALICE data). The reason for this is related to the dynamics of kaon production. This energy behavior of $R_K$ does practically not depend on the sort of beam or target.

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arXiv2026

Nuclear transverse momentum dependent gluon density at low $x$ and inclusive soft hadron production in proton-lead collisions at LHC

We report the results of calculations of inclusive soft hadron production in proton-lead collisions at the LHC in the framework of modified quark-gluon string model (QGSM) extended to $pA$ interactions. Our consideration involves the nuclear modification of previously proposed transverse momentum dependent (TMD, or unintegrated) gluon density in a proton, which provides a self-consistent simultaneous description of numerous HERA and LHC data on $pp$, $ep$ and $γp$ processes. Such nuclear modification is based on well established property of geometrical scaling from nucleons to nuclei. Focusing on the region of small $x$ and low scales, we obtain predictions for transverse momentum spectra of pions and kaons at $p_T \leq 1$~GeV. Our results are compared with recent data reported by the CMS, ATLAS and ALICE Collaborations at $\sqrt s = 5.02$~TeV. We find that the developed approach provides a better description of low-$p_T$ data than the predictions made by other groups.

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arXiv2025

On the gluon shadowing effect in light and heavy nuclei at small $x$

We propose new Transverse Momentum Dependent (TMD) gluon densities in nuclei. Our method is based on a combination of the color dipole scattering formalism, within which we interpret the nuclear deep inelastic structure functions $F_2^{A}(x, Q^2)$ and well established property of geometrical scaling from nucleons to nuclei. As an input, we employ the TMD gluon density in a proton which provides a self-consistent simultaneous description of the numerous HERA and LHC data on $pp$, $ep$ and $γp$ processes. After fitting the relevant phenomenological parameters to the experimental data on the ratios $F_2^{A}(x, Q^2)/F_2^{A^\prime}(x, Q^2)$ for several nuclear targets $A$ and $A^\prime$, we derive the corresponding nuclear gluon distributions. Then, we make predictions for gluon shadowing effects at small Bjorken $x$ in their dependence of the mass number $A$. A comparison with other approaches is given.

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arXiv2025

Intrinsic charm and $D^+D^-$ asymmetry produced in proton-proton collisions

We investigate the contribution of the charm-anticharrm ($c{\bar c}$) asymmetry of the proton eigenstate obtained from QCD lattice gauge to the asymmetry of $D^+D^-$ and $D^0{\bar D}^0$ mesons produced in $pp$ collisions at large Feynman variables $x$. It is shown that an important tool for the establishing the intrinsic charm (IC) content of the proton is the charm hadron-antihadron asymmetry formed in $pp$ collisions. Predictions for the asymmetry as function of $x$ for different IC probabilities are presented. We show that the interference of the intrinsic $|uud c{\bar c}>$ Fock state with the standard contribution from the PQCD evolution leads to a large $D^+D^-$ asymmetry at large Feynman $x$.

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arXiv2024

Refined TMD gluon density in a proton from the HERA and LHC data

We update the phenomenological parameters of the Transverse Momentum Dependent (TMD, or unintegrated) gluon density in a proton proposed in our previous studies. This analysis is based on the analytical expression for starting gluon distribution which provides a self-consistent simultaneous description of HERA data on proton structure function $F_2(x,Q^2)$, reduced cross section for the electron-proton deep inelastic scattering at low $Q^2$ and soft hadron production in $pp$ collisions at the LHC conditions. We extend it to the whole kinematical region using the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. Exploiting our previous results on a number of semihard QCD processes, we performed a combined fit to an extended set of LHC and HERA data, comprising a total of $509$ points from $16$ data sets. We illustrate our fit by applying the derived TMD gluon density in a proton to inclusive prompt photon photoproduction at HERA.

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arXiv2024

Production of charged kaons in $Ar Sc$ collisions

Inclusive spectra of the kaons produced in $Ar Sc$ collisions as functions of their transverse momentum $p_T$ at mid-rapidity have been calculated within the approach based on the assumption of the similarity of inclusive spectra of the hadrons produced in nucleus-nucleus collisions at their small transverse momenta in the mid-rapidity region taking into account the quark-gluon dynamics in nucleon-nucleon interactions. This article gives a satisfactory description of NA61/SHINE data on $p_T$-spectra of the $K^\pm$ mesons produced in $ArSc$ collisions at the mid-rapdity ($y\simeq$ 0).

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arXiv2023

Self-consistent description of HERA data at low $Q^2$ and soft hadron production at LHC

Using the analytical expression for transverse momentum dependent (TMD) gluon density in a proton, a self-consistent simultaneous description of low $Q^2$ data on proton structure function $F_2(x,Q^2)$, reduced cross section for the electron-proton deep inelastic scattering at HERA and soft hadron production in $pp$ collisions at the LHC is achieved in the framework of color dipole approach and modified quark-gluon string model.

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arXiv2022

Towards the global fit of the TMD gluon density in the proton from the LHC data

We propose a new analytical expression for the Transverse Momentum Dependent (TMD, or unintegrated) gluon density in the proton. Essential phenomenological parameters are extracted from the LHC data on inclusive hadron production in $pp$ collisions at low transverse momenta, $p_T \sim 1$~GeV. The latter are described in the framework of modified soft quark-gluon string model, where gluonic state and non-zero transverse momentum of partons inside the proton are taken into account. To determine the parameters important at moderate and large $x$ we used measurements of inclusive $b$-jet and Higgs boson production at the LHC as well as latest HERA data on proton structure functions $F_2^c(x, Q^2)$ and $F_2^b(x, Q^2)$ and reduced cross sections $σ_{\rm red}^{c}(x,Q^2)$ and $σ_{\rm red}^{b}(x,Q^2)$. The Catani-Ciafaloni-Fiorani-Marchesini evolution equation is applied to extend the initial gluon distribution into the whole kinematical region. We have achieved simultaneous description of all considered processes with $χ^2/d.o.f. = 2.2$, thus moving forward to the global fit of TMD gluon density from collider data. The obtained TMD gluon distribution in a proton is available for public usage and implemented into the TMDlib package and Monte-Carlo event generator PEGASUS.

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arXiv2022

Probing the proton structure with associated vector boson and heavy flavor jet production at the LHC

We consider the production of $Z$ bosons associated with heavy (charm and beauty) jets at the LHC energies using two scenarios based on the transverse momentum dependent (TMD) parton densities in a proton. The first of them employs the Catani-Ciafaloni-Fiorani-Marchesini gluon evolution and is implemented in the Monte-Carlo event generator PEGASUS. Here, the heavy quarks are always produced in the hard partonic scattering. The second scheme is based on the parton branching approach, currently implemented into the Monte-Carlo event generator CASCADE. In this scenario, the $Z$ + jets sample is generated and then events containing the heavy flavor jet in a final state are selected. We compare the predictions obtained within these two TMD-based approaches to each other, investigate their sensitivity to the TMD gluon densities in a proton and estimate the effects coming from parton showers and double parton scattering mechanism. Additionally, we compare our predictions with the results of traditional (collinear) pQCD calculations performed at NLO accuracy. It is shown that the TMD-based results agree with the LHC experimental data collected at $\sqrt s = 8$ and $13$ TeV. We discuss the sensitivity of observables to the quark distributions in a proton and present predictions to search for the intrinsic charm signal in forthcoming analyses of the LHC experimental data.

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arXiv2022

Ratio of kaon-to-pion production cross-sections in $Be Be$ collisions as a function of $\sqrt{s}$

The inclusive spectra of pions and kaons produced in $Be Be$ collisions as functions of their transverse momentum $p_t$ at mid-rapidity are calculated within the self-similarity approach. A satisfactory description of NA61/SHINE data on these spectra and the ratio of $K^\pm$ to $π^\pm$ meson production cross sections in $Be Be$ collisions as a function of $\sqrt{s}$ are presented. The similarity of these observables to the ones for $pp$ collisions at mid-rapidity and in the wide range of initial energies is illustrated.

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arXiv2021

Ratio of cross-sections of kaons to pions produced in $pp$ collisions as a function of $\sqrt{s}$

A calculation of the inclusive spectra of pions and kaons produced in $pp$ collisions as functions of their transverse momentum $p_t$ at mid-rapidity is presented within the self-similarity approach. A satisfactory description of the data within a wide range of initial energies is presented. We focus mainly on the ratio of cross-sections of $K^\pm$ to $π^\pm$ mesons produced in $pp$ collisions as a function of $\sqrt{s}$. A fast rise of this ratio, when the initial energy increases starting from the kaon production threshold up to $\sqrt{s}\simeq$ 20-30 Gev, is revealed together with its very slow increase up to LHC energies. The energy dependence of this ratio is due to the conservation laws of four-momenta and quantum numbers of the initial and produced hadrons, and to the Regge behavior of cross-sections at large energies. The more or less satisfactory agreement of these ratios with NA61-SHINE, RHIC and LHC data is demonstrated.

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arXiv2020

Novel Heavy-Quark Physics Phenomena

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 $x_\mathrm{F}$ 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 $G_\mathrm{E}^p(Q^2)$ form factor. 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 $c(x,Q) - \bar{c}(x,Q)$ 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 $\sqrt{s} = 8$ TeV 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.

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arXiv2019

Mid-rapidity dependence of hadron production in $p-p$ and $A-A$ collisions

The calculation of inclusive spectra of pions produced in $pp$ and $AA$ collisions as a function of rapidity $y$ is presented within the self-similarity approach. It is shown that at not large rapidities $y$ one can obtain the analytical form of the self-similarity function $Π(y,p_t)$ dependent of $y$ and hadron transverse momentum $p_t$. A satisfactory description of data on the rapidity spectra at $|y|\leq$ 0.3 is illustrated within a good agreement. The universal energy dependence of these spectra is also shown.

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arXiv2019

Dielectron production in pion-nucleon reactions and form factor of baryon transition within the time-like region

Dielectron production in reactions $π^- p \rightarrow n e^+e^-$ and $π^- p \rightarrow n e^+e^- γ$ at energies less than 1 GeV is studied assuming electron-positron pair production to occur in the virtual time-like photon splitting process. Theoretical predictions of the effective mass distribution of dielectrons and their angular dependence are presented. Extraction of the electromagnetic form factor of baryon transition in the time-like region from future experiments of the HADES Collaboration is discussed.

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arXiv2018

Self-consistent analysis of hadron production in $pp$ and $AA$ collisions at mid-rapidity

The self-consistent approach based on similarity of inclusive spectra of hadrons produced in $pp$ and $AA$ collisions is reviewed. This approach allows us to describe rather well the ratio of proton to anti-proton yields in $AA$ collisions as a function of the initial energy at a wide range from a few GeV to a few TeV. 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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arXiv2018

Constraints on the intrinsic charm content of the proton from recent ATLAS data

Constraints on the intrinsic charm probability $\wccm = P_{{\mathrm{c}\bar \mathrm{c}} / \mathrm{p}}$ in the proton are obtained for the first time from LHC measurements. The ATLAS Collaboration data for the production of prompt photons, accompanied by a charm-quark jet in pp collisions at $\sqrt s = 8 $ TeV, are used. The upper limit \mbox{$\wccm < 1.93$~\%} 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.

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arXiv2018

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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arXiv2018

Hard production of a Z boson plus heavy flavor jets at LHC and the intrinsic charm content of a proton

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 $p_T$ 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 non-zero 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.

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