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A. V. Lipatov

Publications and source records attributed to A. V. Lipatov.

At least 19 recordsLinked to original sources
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.

hep-ph↗
arXiv2026

Testing the nuclear TMD gluon densities with heavy flavor production in proton-lead collisions at LHC

We employ a simple model for nuclear modification of ordinary parton densities in a proton to evaluate the Transverse Momentum Dependent gluon and quark distributions in nuclei (nTMDs) within the popular Kimber-Martin-Ryskin/Watt-Martin-Ryskin approach. The model is based on a global analysis of available deep inelastic scattering data for different nuclear targets within the rescaling model, incorporating Fermi motion effects. The derived nTMDs are tested with latest CMS data on inclusive $b$-jet and $B^+$ meson production in proton-lead collisions collected at $\sqrt s = 5.02$ and $8.16$~TeV using the High Energy Factorization framework. We predict the corresponding nuclear medium modification factors to be about of $0.8 - 1.2$ in the probed kinematical region, which is consistent with other estimations. Specially we highlight a possibility to investigate the nuclear modification of parton densities by applying different cuts on the final states in such processes.

hep-ph↗
arXiv2025

A simple model for PDFs and nPDFs

We present the main results of our recent papers, where we derived an analytical solution of the QCD evolution equations for parton distribution functions. The valence and non-singlet quark components satisfy the Gross-Llewellyn-Smith and Gottfried sum rules, respectively, while momentum conservation is maintained for the singlet quark and gluon densities. Several phenomenological parameters were extracted from a combined fit to precision data on the proton structure function $F_2(x,Q^2)$ collected by the BCDMS, H1, and ZEUS Collaborations, comprising a total of 933 points from 5 datasets. We proposed a model for nuclear medium modifications of parton densities. The approach is based on a global analysis of available deep inelastic scattering data for different nuclear targets within the rescaling model, incorporating Fermi motion effects. By fitting the rescaling parameters to experimental data on the ratio $F_2^A(x,Q^2)/F_2^{D}(x,Q^2)$ for several nuclear targets $A$, we obtained predictions for nuclear parton distribution functions.

hep-ph↗
arXiv2025

Transverse momentum dependent gluon density in a proton at low $x$ in the Laplace transform method

We investigate the gluon distribution in a proton at very low $x$, both integrated and transverse momentum dependent, using the Laplace transform technique. By accounting for leading and main next-to-leading contributions, we derive compact analytical expressions for the gluon densities valid in the asymptotic limit $x \to 0$. Our results closely match those from other analytical and numerical approaches, with the main advantage being the simplicity of the expressions, which capture the essential features of more complex calculations.

hep-ph↗
arXiv2025

A simple model for nuclear modification of parton distribution functions

A model for nuclear medium modification of parton densities is presented. The approach is based on the global analysis of available deep inelastic scattering data for different nuclear targets within the rescaling model combined with taking into account the effects of Fermi motion. The scale dependence is implemented into the DGLAP-evolved quark and gluon densities in a proton derived analytically at the leading order of QCD coupling. By fitting the rescaling parameters to experimental data on the ratio $F_2^A(x,Q^2)/F_2^{A^\prime}(x,Q^2)$ for several nuclear targets $A$ and $A^\prime$, we obtain redictions for nuclear parton distributions, even for unmeasured nuclei. The effects of nuclear modifications are investigated with respect to the mass number $A$. Our results highlight distinct shadowing and antishadowing behaviors for gluons and quarks.

hep-ph↗
arXiv2025

Tree-level NLO corrections to inclusive $ψ'$ production in High Energy Factorization

We consider inclusive $ψ(2S)$ production in proton-proton collisions at collider energies in the framework of non-relativistic QCD and high-energy factorization beyond the low-order approximation. We utilise a matching scheme proposed earlier to merge the leading order and tree-level next-to-leading order production amplitudes and now extend it to low transverse momenta and/or forward rapidities. With the improved scheme, we examine the possibility to simultaneously describe all unpolarized LHC data in the full kinematic range accessible to experimental measurements and try different Transverse Momentum Dependent (TMD) gluon distributions in the proton. A global fit to the data is carried out to extract the color octet long-distance matrix elements for $ψ(2S)$ mesons. We show that taking the NLO corrections into account leads to better description of the data.

hep-ph↗
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.

hep-ph↗
arXiv2025

Updating TMD parton densities in a proton within the Kimber-Martin-Ryskin approach

We present analytical expressions for the Transverse Momentum Dependent (TMD, or unintegrated) gluon and quark densities in a proton derived at leading order of QCD running coupling and valid at both small and large x. The calculations are performed using the Kimber-Martin-Ryskin/Watt-Martin-Ryskin prescription (in both differential and integral formulations) with different treatment of kinematical constraint, which reflects the angular and strong ordering conditions for parton emissions. As an input, analytical solution of QCD evolution equations for conventional (collinear) parton distributions is applied, where the valence and non-singlet quark parts obey the Gross-Llewellyn-Smith and Gottfried sum rules and momentum conservation for the singlet quark and gluon densities is taken into account. Several phenomenological parameters are extracted from combined fit to precision data on the proton structure function $F_2(x,Q^2)$ collected by the BCDMS, H1 and ZEUS Collaborations, comprising a total of 933 points from 5 data sets. Comparison with the numerical results obtained by other groups is presented and phenomenological application to the inclusive b-jet production at the LHC is given.

hep-ph↗
arXiv2024

Forward $J/ψ+ J/ψ$ and $J/ψ+ ψ^\prime$ production with High Energy Factorization

We calculate the cross sections of associated $J/ψ+ ψ^\prime$ and $J/ψ+ J/ψ$ production in $pp$ collisions at $\sqrt s = 13$ TeV in the forward kinematic region. The High Energy Factorization ($k_T$-factorization) framework supplemented with the Catani-Ciafaloni-Fiorani-Marchesini evolution of gluon densities in a proton is applied. We demonstrate that latest data on $J/ψ+ J/ψ$ production and first experimental data on $J/ψ+ ψ^\prime$ events taken very recently by the LHCb Collaboration can be described well by the color singlet terms and contributions from the double parton scattering (DPS) with the standard choice for $σ_{\rm eff}$ parameter. The relative production rate $σ(J/ψ+ ψ^\prime)/σ(J/ψ+ J/ψ)$ is found to be sensitive to the DPS terms as well as to feeddown contributions.

hep-ph↗
arXiv2024

Double parton scattering versus jet quenching

A novel observable, the double nuclear modification factor, is proposed to probe simultaneously the initial and final state effects in nucleus-nucleus collisions. An interesting competition between the combinatorial enhancement in the double parton scattering and the suppression due to parton energy loss can be observed in the production rate of two hard particles. In particular, the production of $J/ψ$ mesons in association with a $W$ boson is not suppressed but is enhanced in the region of moderate transverse momenta, unlike the case of unassociated (inclusive) $J/ψ$ production. At the same time, in the region of high enough transverse momenta the nuclear modification factor for associated $J/ψ+W$ production converges to that of unassociated $J/ψ$.

nucl-th↗
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.

hep-ph↗
arXiv2024

Shadowing and antishadowing in the rescaling model

Nuclear deep inelastic structure functions F_2^A(x,Q^2) as well as parton distribution functions in a nuclei are investigated in the framework of rescaling model. Our analysis is based on analytical expressions for quark and gluon densities in a proton derived at the leading order of QCD coupling. By fitting the rescaling parameters from the experimental data on F_2^A(x,Q^2)/F_2^D(x,Q^2) ratio for several nuclear targets, we derive predictions for corresponding nuclear parton distributions and, thus, for shadowing and antishadowing effects.

hep-ph↗
arXiv2023

TMD gluon density in nuclei versus experimental data on heavy flavor production at LHC

Analytical expressions for the Transverse Momentum Dependent (TMD, or unintegrated) gluon and sea quark densities in nuclei are derived at leading order of QCD running coupling. The calculations are performed in the framework of the rescaling model and Kimber-Martin-Ryskin (KMR) prescription, where the Bessel-inspired behavior of parton densities at small Bjorken $x$ values, obtained in the case of flat initial conditions in the double scaling QCD approximation, is applied. The derived expressions are used to evaluate the inclusive heavy flavor production in proton-lead collisions at the LHC. We find a good agreement of our results with latest experimental data collected by the CMS and ALICE Collaborations at $\sqrt s = 5.02$ GeV.

hep-ph↗
arXiv2023

Towards higher-order calculations of quarkonia production with $k_T$-factorization: $P$-wave charmonia

Inclusive $P$-wave charmonia production in hadronic collisions at high energies is discussed in the framework of non-relativistic QCD and $k_T$-factorization formalism. We present two consistent approches to merge the usual leading order $k_T$-factorization calculations with tree-level next-to-leading order off-shell amplitudes. Using these prescriptions, we extracted long-distance matrix elements for $χ_c$ mesons from a combined fit to available Tevatron and LHC data. In contrast to previous (leading order) calculations, our fits do not contradict equal color singlet wave functions of $χ_{c1}$ and $χ_{c2}$ states. The extracted values of long-distance matrix elements are employed to analyse the $χ_c$ polarization data reported recently by the CMS Collaboration. Our predictions are in a reasonably good agreement with the Tevatron and LHC measurements within the theoretical and experimental uncertainties.

hep-ph↗
arXiv2023

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.

hep-ph↗
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.

hep-ph↗
arXiv2023

TMD parton showers for associated $γ$+jet production in electron-proton collisions at high energies

An earlier developed $k_T$-factorization framework to calculate the associated prompt photon and hadronic jets production cross sections at high energies is extended now to the electron-proton deep inelastic scattering. The proposed method is based on joint usage of the PEGASUS and CASCADE Monte-Carlo event generators, which deal with the transverse momentum dependent (TMD) gluon and quark densities in a proton. First of them, PEGASUS, is applied to produce off-shell photon-gluon fusion events. Then, to properly simulate the kinematics of the produced jets, the TMD parton shower algorithm implemented into the CASCADE is used. We demonstrate basic features of the approach considering latest H1 and ZEUS data on prompt photon plus jet production at low $Q^2$ collected at HERA. We achieve a good description of the measurements and point out that a correct simulation of parton showers is essential for studying non-inclusive processes at high energies within the TMD-based approaches.

hep-ph↗