Searcharxiv⌕ Search

arXiv subjects

A. V. Lipatov

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

At least 55 records · Page 3Linked to original sources
arXiv2019

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.

hep-ph↗
arXiv2019

TMD parton shower effects in associated $γ$ + jet production at LHC

We investigate associated prompt photon and hadronic jet production at the LHC energies using the $k_T$-factorization approach. Our consideration is based on the $\mathcal O(αα_s^2)$ off-shell gluon-gluon fusion subprocess $g^*g^*\to γq\bar q$ and several subleading quark-initiated contributions from $\mathcal O(αα_s)$ and $\mathcal O(αα_s^2)$ subprocesses, taken into account in the conventional (collinear) QCD factorization. The transverse momentum dependent (or unintegrated) gluon densities in a proton are derived from Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. We achieve reasonably good agreement with the experimental data taken by CMS and ATLAS Collaborations and demonstrate the importance of initial state parton showers for jet determination in the $k_T$-factorization approach.

hep-ph↗
arXiv2019

Are there any challenges in the charmonia production and polarization at the LHC?

We analyze the inclusive prompt production of $ψ^\prime$, $χ_c$, $J/ψ$ and $η_c$ mesons at the LHC using the $k_T$-factorization approach. Our consideration is based on the off-shell production amplitudes for hard partonic subprocesses, nonrelativistic QCD formalism for the formation of bound states and transverse momentum dependent (or unintegrated) gluon densities in a proton derived from Catani-Ciafaloni-Fiorani-Marchesini equation. The nonperturbative color octet transitions are treated in terms of the multipole radiation theory. We extract the corresponding long-distance matrix elements from a combined fit to transverse momentum distributions measured at various LHC experiments. We make predictions for the polarization parameters $λ_θ$, $λ_ϕ$, $λ_{θϕ}$ and the frame-independent parameter $λ^*$ and compare them to the available $ψ^\prime$ and $J/ψ$ data. Finally, we present a universal set of parameters that provides a reasonable simultaneous description for the whole body of the LHC data (on the $p_T$ distributions, relative production rates and polarization observables) for the whole charmonium family.

hep-ph↗
arXiv2019

Prompt $η_c$ meson production at the LHC in the NRQCD with $k_T$-factorization

In the framework of the $k_T$-factorization, the prompt production of $η_c$ mesons at the LHC conditions is studied. Our consideration is based on the off-shell amplitudes for hard partonic subprocesses and on the nonrelativistic QCD (NRQCD) formalism for the formation of bound states. We try two latest parametrizations for noncollinear, or transverse momentum dependent (TMD) gluon densities derived from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) equation. We use the values of the nonperturbative matrix elements obtained from a combined fit of the $η_c$ and $J/ψ$ differential cross sections. Finally, we show an universal set of parameters that provides a reasonable simultaneous description for all of the available data on the prompt $J/ψ$ and $η_c$ production at the LHC.

hep-ph↗
arXiv2018

Associated non-prompt $J/ψ+ μ$ and $J/ψ+ J/ψ$ production at LHC as a test for TMD gluon density

We consider the associated production of $J/ψ$ mesons and muons originating from the $b$-flavored hadron decays and non-prompt double $J/ψ$ production at the LHC using the $k_T$-factorization approach. To describe the inclusive $b$-hadron decays into the different charmonium states we apply fragmentation approach and adopt fragmentation functions based on the non-relativistic QCD factorization. The transverse momentum dependent (TMD) gluon densities in a proton are determined using the Catani-Ciafaloni-Fiorani-Marchesini equation and Kimber-Martin-Ryskin prescription. We investigate the effects coming from parton showers, estimate the double parton scattering contribution and compare our predictions with the first experimental data taken by the ATLAS and LHCb Collaborations at $\sqrt s = 8$~TeV. These data can serve as an additional test for TMD gluon density function in a proton.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
arXiv2017

Associated production of $Z$ bosons and $b$-jets at the LHC in the combined $k_T$ + collinear QCD factorization approach

We consider the production of $Z$ bosons associated with beauty quarks at the LHC using a combined $k_T$ + collinear QCD factorization approach, that interpolates between small $x$ and large $x$ physics. Our consideration is based on the off-shell gluon-gluon fusion subprocess $g^* g^* \to Z Q\bar Q$ at the leading order ${\cal O}(αα_s^2)$ (where the $Z$ boson further decays into a lepton pair), calculated in the $k_T$-factorization approach, and several subleading ${\cal O}(αα_s^2 )$ and ${\cal O}(αα_s^3 )$ subprocesses involving quark-antiquark and quark-gluon interactions, taken into account in conventional (collinear) QCD factorization. The contributions from double parton scattering are discussed as well. The transverse momentum dependent (or unintegrated) gluon densities in a proton are derived from Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. We achieve reasonably good agreement with the latest data taken by CMS and ATLAS Collaborations. The comparison of our results with next-to-leading-order pQCD predictions, obtained in the collinear QCD factorization, is presented. We discuss the uncertainties of our calculations and demonstrate the importance of subleading quark involving contributions in describing the LHC data in the whole kinematic region.

hep-ph↗
arXiv2017

Charmonia production from $b$-hadron decays at LHC with $k_T$-factorization: $J/ψ$, $ψ(2S)$ and $J/ψ+ Z$

We consider the production of $J/ψ$ and $ψ(2S)$ mesons originating from the decays of $b$-flavored hadrons at the LHC using the $k_T$-factorization approach. Our analysis covers both inclusive charmonia production and production of $J/ψ$ mesons in association with $Z$ bosons. We apply the transverse momentum dependent (or unintegrated) gluon density in a proton derived from Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation and adopt fragmentation functions based on the non-relativistic QCD factorization to describe the inclusive $b$-hadron decays into the different charmonium states. Our predictions agree well with latest experimental data taken by the CMS, ATLAS and LHCb Collaborations at $\sqrt s = 7$, $8$ and $13$~TeV. The contributions from double parton scattering to the associated non-prompt $J/ψ+ Z$ production are estimated and found to be small.

hep-ph↗
arXiv2017

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.

hep-ph↗
arXiv2017

Phenomenology of kt-factorization for inclusive Higgs boson production at LHC

We investigate the inclusive Higgs boson production in proton-proton collisions at high energies in the framework of kt-factorization QCD approach. The attention is focused on the dominant off-shell gluon-gluon fusion subprocess, where the transverse momentum of incoming gluons are taken into account. The transverse momentum dependent (or unintegrated) gluon densities of the proton are determined using the CCFM evolution equation as well as the Kimber-Martin-Ryskin prescription. We study the theoretical uncertainties of our calculations and perform the comparison with the results of traditional pQCD evaluations. Our predictions agree well with the first experimental data taken by the ATLAS collaboration at the LHC. We argue that further studies of the Higgs boson production are capable of constraining the unintegrated gluon densities of the proton.

hep-ph↗
arXiv2016

On possible small-x effects in the Kaluza-Klein graviton and radion production at high energies

We study the single graviton production at the CERN LHC using the $k_T$-factorization approach of QCD. We consider the Arkani-Hamed-Dimopoulos-Dvali scenario and Randall-Sundrum model with one warped extra-dimension and derive the production amplitudes for spin-$2$ (Kaluza-Klein excitation of the graviton) and spin-$0$ (radion) states, including subsequent graviton decay into the dilepton or diphoton pairs. We use the transverse momentum dependent (unintegrated) parton densities in a proton obtained from Ciafaloni-Catani-Fiorani-Marchesini (CCFM) evolution equation, which resums the leading logarithmic small-$x$ corrections to the production cross sections. We demonstrate that the small-$x$ effects can manifest themselves in the different angular distributions of graviton decay products and give some examples of how these distributions can look like at the LHC energies.

hep-ph↗
arXiv2016

Prompt charmonia production and polarization at LHC in the NRQCD with $k_T$-factorization. Part III: $J/ψ$ meson

In the framework of $k_T$-factorization approach, the production and polarization of prompt $J/ψ$ mesons at the LHC energies is studied. Our consideration is based on the non-relativistic QCD formalism for bound states and off-shell amplitudes for hard partonic subprocesses. Both the direct production mechanism and feed-down contributions from $χ_c$ and $ψ(2S)$ decays are taken into account. The transverse momentum dependent (or unintegrated) gluon densities in a proton were derived from Ciafaloni-Catani-Fiorani-Marchesini evolution equation or, alternatively, were chosen in accordance with Kimber-Martin-Ryskin prescription. The non-perturbative color-octet matrix elements were first deduced from the fits to the latest CMS data on $J/ψ$ transverse momentum distributions and then applied to describe the ATLAS and LHCb data on $J/ψ$ production and polarization at $\sqrt s = 7$, $8$ and $13$ TeV. We perform an estimation of polarization parameters $λ_θ$, $λ_ϕ$ and $λ_{θϕ}$ which determine $J/ψ$ spin density matrix and demonstrate that treating the soft gluon emission as a series of explicit color-electric dipole transitions within NRQCD leads to unpolarized $J/ψ$ production at high transverse momenta, that is in qualitative agreement with the LHC data.

hep-ph↗
arXiv2016

Probing proton intrinsic charm in photon or Z boson production accompanied by heavy jets at LHC

We consider an observable very sensitive to the non-zero 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 $p_T$ and their pseudo-rapidities $1.5 < η< 2.4$ if the IC contribution is taken into account. On the contrary, in the absence of the IC this ratio decreases as $p_T$ grows. We also present the ratios of the cross sections integrated over $p_T$ 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 $p_T$-spectra, which significantly depend on these uncertainties.

hep-ph↗
arXiv2016

Testing the parton evolution with the use of two-body final states

We consider the production of $b\bar b$ quarks and Drell-Yan lepton pairs at LHC conditions focusing attention on the total transverse momentum of the produced pair and on the azimuthal angle between the momenta of the outgoing particles. Plotting the corresponding distributions in bins of the final state invariant mass, one can reconstruct the full map of the transverse momentum dependent parton densities in a proton. We give examples of how can these distributions can look like at the LHC energies.

hep-ph↗
arXiv2016

Reconsideration of the inclusive prompt photon production at LHC with kt-factorization

We reconsider the inclusive production of isolated prompt photons in $pp$ collisions at the LHC energies in the framework of $k_T$-factorization approach. Our analysis is based on the ${\cal O}(αα_s)$ off-shell (depending on the transverse momenta of initial quarks and gluons) production amplitudes of $q^* g^* \to γq$ and $q^* \bar q^* \to γg$ partonic subprocesses and transverse momentum dependent (or unintegrated) quark and gluon densities in a proton, which are chosen in accordance with the Kimber-Martin-Ryskin prescription. We show that the sub-leading high-order ${\cal O}(αα_s^2)$ contributions, not covered by the non-collinear evolution of parton densities, are important to describe latest LHC data.

hep-ph↗