arXiv subjects

M. A. Malyshev

Publications and source records attributed to M. A. Malyshev.

35 records · Page 2Linked to original sources

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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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.

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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.

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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.

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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.

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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.

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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.

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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.

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arXiv2016

Associated production of electroweak bosons and heavy mesons at LHCb and prospects to observe double parton interactions

The production of weak gauge bosons in association with heavy flavored mesons at the LHCb conditions is considered, and a detailed study of the different contributing processes is presented including single (SPS) and double (DPS) parton scattering mechanisms. We find that the usual DPS factorization formula needs to be corrected for the limited partonic phase space, and that including the relevant corrections reduces discrepancies in the associated $ZD$ production. We conclude finally that double parton scattering dominates the production of same-sign $W^\pm D^\pm$ states, as well as the production of $W^-$ bosons associated with $B$-mesons. The latter processes can thus be regarded as new useful DPS indicators.

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arXiv2015

Associated $W^{\pm}D^{(*)}$ production at the LHC and prospects to observe double parton interactions

Associated production of charged gauge bosons and charged charmed mesons at the LHC is considered in the framework of $k_T$-factorization approach. Theoretical predictions are compared with ATLAS data, and reasonably good agreement is found. Predictions on the same-sign $W^{\pm}D^{\pm}$ configurations are presented including single parton scattering and double parton scattering contributions. The latter are shown to dominate over the former, thus giving evidence that the proposed process can serve as another indicator of double parton interactions.

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arXiv2013

An extended study of the prompt photon photoproduction at HERA with $k_T$-factorization

We reconsider the prompt photon photoproduction at HERA in the framework of the $k_T$-factorization QCD approach. The proposed method is based on the ${\cal O}(α^2α_s)$ amplitudes for $γq\toγgq$ and $γg^*\toγq\bar q$ partonic subprocesses. Additionally, we take into account the ${\cal O}(α^2α_s^2)$ box contributions $γg\toγg$ to the production cross sections. The unintegrated (or transverse momentum dependent) parton densities in the proton are determined using Kimber-Martin-Ryskin (KMR) prescription. Our consideration covers both inclusive and jet associated prompt photon photoproduction rates. We find that our numerical predictions agree well with the recent data taken by H1 and ZEUS collaborations at HERA. We demonstrate that the box contributions are sizeable and amount up to $\sim15%$ of the calculated total cross section.

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arXiv2013

Associated photon and heavy quark production at high energy within k_T-factorization

In the framework of the k_T-factorization approach, the production of prompt photons in association with a heavy (charm or beauty) quarks at high energies is studied. The consideration is based on the O(αα_s^2) off-shell amplitudes of gluon-gluon fusion and quark-(anti)quark interaction subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin prescription. Our numerical predictions are compared with the D0 and CDF experimental data. Also we extend our results to LHC energies.

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arXiv2012

Prompt photon and associated heavy quark production at hadron colliders with kt-factorization

In the framework of the kt-factorization approach, the production of prompt photons in association with a heavy (charm or beauty) quarks at high energies is studied. The consideration is based on the O(αα_s^2) off-shell amplitudes of gluon-gluon fusion and quark-(anti)quark interaction subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The analysis covers the total and differential cross sections and extends to specific angular correlations between the produced prompt photons and muons originating from the semileptonic decays of associated heavy quarks. Theoretical uncertainties of our evaluations are studied and comparison with the results of standard NLO pQCD calculations is performed. Our numerical predictions are compared with the recent experimental data taken by the D0 and CDF collaborations at the Tevatron. Finally, we extend our results to LHC energies.

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arXiv2011

Drell-Yan lepton pair production at high energies in the kt-factorization approach

In the framework of the kt-factorization approach, the production of unpolarized Drell-Yan lepton pair at high energies is studied. The consideration is based on the O(alpha) and $O(alpha alpha_s) off-shell partonic matrix elements with virtual photon and Z boson exchange. The calculations include leptonic decays of Z bosons with full spin correlations as well as gamma - Z interference. The unintegrated parton densities in a proton are determined by the Kimber-Martin-Ryskin prescription. Our numerical predictions are compared with the data taken by the D0, CDF and CMS collaborations at the Tevatron and LHC energies. Special attention is put on the specific angular distributions measured very recently by the CDF collaboration for the first time.

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arXiv2011

Testing for kt-factorization with inclusive prompt photon production at LHC

We study the possibility to analyse the data on inclusive prompt photon production at first LHC runs in the framework of the kt-factorization QCD approach. Our consideration is based on the amplitude for the production of a single photon associated with a quark pair in the fusion of two off-shell gluons. The quark component is taken into account separately using the quark-gluon Compton scatterring and quark-antiquark annihilation QCD subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin (KMR) prescription as well as the CCFM evolution equation.

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