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N. P. Zotov

Publications and source records attributed to N. P. Zotov.

At least 19 recordsLinked to original sources
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

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.

hep-ph↗
arXiv2016

Significance of non-perturbative input to TMD gluon density for hard processes at LHC

We study the role of the non-perturbative input to the transverse momentum dependent (TMD) gluon density in hard processes at the LHC. We derive the input TMD gluon distribution at low scale mu0^2 ~ 1 GeV^2 from the fit of the inclusive hadron spectra measured at low transverse momenta in pp collisions at the LHC and demonstrate that the best description of these spectra for larger hadron transverse momenta can be achieved by matching the derived TMD gluon distribution with the exact solution of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation obtained at low x and small gluon transverse momenta outside the saturation region. Then, we extend the input TMD gluon density to higher mu^2 numerically using the Catani-Ciafoloni-Fiorani-Marchesini (CCFM) gluon evolution equation. A special attention is put to the phenomenological applications of obtained TMD gluon density to some LHC processes, which are sensitive to the gluon content of a proton.

hep-ph↗
arXiv2015

Prompt charmonia production and polarization at LHC in the NRQCD with kt-factorization. Part II: $χ_c$ mesons

In the framework of kt-factorization approach,the production of prompt $χ_c$ mesons in pp collisions at the LHC energies is studied. Our consideration is based on the off-shell amplitudes for hard partonic subprocesses $g^*g^*\toχ_{cJ}$ and non-relativistic QCD formalism for bound states. The transverse momentum dependent (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. Taking into account both color singlet and color octet contributions, we deduce the corresponding non-perturbative long-distance matrix elements from the fits to the latest ATLAS data on $χ_{c1}$ and $χ_{c2}$ transverse momentum distributions at $\sqrt s = 7$ TeV. We find that these distributions at small and moderate pt are formed mainly by the color singlet components. We successfully described the data on the differential cross sections and relative production rates $σ(χ_{c2})/σ(χ_{c1})$ presented by the ATLAS, CMS and LHCb Collaborations. We find that the fit points to unequal wave functions of $χ_{c1}$ and $χ_{c2}$ states.

hep-ph↗
arXiv2015

Prompt charmonia production and polarization at LHC in the NRQCD with kt-factorization. Part I: psi(2S) meson

In the framework of kt-factorization approach, the production and polarization of prompt psi(2S) mesons in pp collisions 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. The transverse momentum dependent (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 psi(2S) transverse momentum distributions and then applied to describe the ATLAS and LHCb data on psi(2S) production and polarization at 7 TeV. We perform the estimation of polarization parameters $λ_θ$, $λ_ϕ$ and $λ_{θϕ}$ which determine psi(2S) spin density matrix and demonstrate that taking into account the off-shellness of initial gluons in the color-octet contributions leads to unpolarized psi(2S) production at high transverse momenta, that is in qualitative agreement with the LHC data.

hep-ph↗
arXiv2015

On the possibility to detect the Higgs decay $H\to b\bar b$ in the associated $Z + b\bar b$ production at the LHC

We investigate the possibility to detect the scalar Higgs boson decay $H\to b\bar b$ in the associated $Z$ and $b\bar b$ production at the LHC using the $k_T$-factorization QCD approach. Our consideration is based on the off-shell (i.e. depending on the transverse momenta of initial quarks and gluons) production amplitudes of $q^* \bar q^* \to Z H \to Z q^\prime \bar q^\prime$, $q^* \bar q^* \to Z q^\prime \bar q^\prime$ and $g^* g^* \to Z q^\prime \bar q^\prime$ partonic subprocesses supplemented with the Catani-Ciafoloni-Fiorani-Marchesini (CCFM) dynamics of parton densities in a proton. We argue that the $H \to b\bar b$ signal could be observed at large transverse momenta near Higgs boson peak despite the overwhelming QCD background, and point out an important role of angular correlations between the produced $Z$ boson and $b$-quarks.

hep-ph↗
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.

hep-ph↗
arXiv2014

TMD PDFs in Drell-Yan lepton pair production at LHC

We consider the transverse momentum dependent (TMD) quark densities of the proton which are very important ingredients for unpolarized Drell-Yan (DY) lepton pair production. We calculate the TMD sea quark density as a convolution of the Catani-Ciafaloni-Fiorani-Marchesini (CCFM)-evolved gluon distribution and the TMD gluon-to-quark splitting function. Based on the ${\cal O}(α^2)$ production amplitude $q^* + \bar q^* \to Z/γ^* \to l^+ + l^-$, calculated by taking into account the effective $q^*\bar q^* Z/γ^*$ - vertex, we analyze the distributions on the dilepton invariant mass, transverse momentum and rapidity and specific angular correlations between the produced leptons as measured by the CMS, ATLAS and LHCb collaborations. We briefly duscuss also the process of assiciated lepton pair and jet production in $pp$ collisions at the LHC.

hep-ph↗
arXiv2014

TMD parton densities in associated real and virtual photon and jet production at LHC

We study the associated production of real (isolated) or virtual photons (with their subsequent leptonic decay) and hadronic jets in proton-proton collisions at the LHC using the $k_T$-factorization approach of QCD. The consideration is based on the off-shell quark-gluon QCD Compton scattering subprocesses. In the case of virtual photon production, the contributions from Z boson exchange as well as gamma*-Z interference with the full spin correlations are included. The transverse momentum dependent (TMD) quark and gluon densities in a proton are determined from the Kimber-Martin-Ryskin prescription or Catani-Ciafoloni-Fiorani-Marchesini (CCFM) equation. In the latter, we restricted to the case where the gluon-to-quark splitting occurs at the last evolution step and calculate the sea quark density as a convolution of the CCFM-evolved gluon distribution and the TMD gluon-to-quark splitting function. Our numerical predictions are compared with the recent experimental data taken by the ATLAS Collaboration. We discuss the theoretical uncertainties of our calculations and argue that further studies are capable of constraining the TMD parton densities in a proton.

hep-ph↗
arXiv2014

Drell-Yan lepton pair production at LHC and TMD quark densities of the proton

We use the TMD quark densities of the proton to investigate unpolarized Drell-Yan lepton pair production in proton-proton collisions at the LHC energies. We investigate the case where the gluon-to-quark splitting occurs at the last evolution step and calculate the TMD sea quark density as a convolution of the CCFM-evolved gluon distribution and the TMD gluon-to-quark splitting function which contains all single logarithmic small-x corrections to the sea quark evolution for any order of perturbation theory. Based on the O(alpha) production amplitude of quark-antiquark annihilation calculated according to the reggeized quark approach, we analyze the distributions on the dilepton invariant mass, transverse momentum and rapidity as well as the specific angular correlations between the produced leptons as measured by the CMS, ATLAS and LHCb collaborations. We argue that these measurements impose stringent constraints on the TMD quark distributions of the proton.

hep-ph↗
arXiv2013

LHC soft physics and TMD gluon density at low x

We study the unintegrated, or transverse momentum dependent (TMD) gluon distribution obtained from the best description of the LHC data on the inclusive spectra of hadrons produced in the mid-rapidity region and low transverse momenta at starting scale Q0^2 = 1 GeV^2. To extend this gluon density at higher Q^2 we apply the Catani-Ciafoloni-Fiorani-Marchesini (CCFM) evolution equation. The influence of the initial (starting) non-perturbative gluon distribution is studied. The application of the obtained gluon density to the analysis of the ep deep inelastic scattering allows us to get the results which describe reasonably well the H1 and ZEUS data on the longitudinal proton structure function FL(x,Q^2). So, the connection between the soft processes at LHC and small x physics at HERA has been confirmed and extended to a wide kinematical region.

hep-ph↗
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.

hep-ph↗
arXiv2013

Interparticle correlations in the production of J/ψpairs in proton-proton collisions

We focus on the problem of disentangling the single (SPS) and double (DPS) parton scattering modes in the production of \J pairs at the LHC conditions. Our analysis is based on comparing the shapes of the differential cross sections and on studying their behavior under imposing kinematical cuts. On the SPS side, we consider the leading-order ${\cal O}(α_s^4)$ contribution with radiative corrections (taken into account in the framework of the \ktf approach) and the subleading ${\cal O}(α_s^6)$ contribution from \pd ~gluon-gluon scattering represented by one gluon exchange and two gluon exchange mechanisms. We come to the conclusion that disentangling the SPS and DPS modes is rather difficult on the basis of azimuthal correlations, while the rapidity difference looks more promising, provided the acceptance of the experimental detectors has enough rapidity range.

hep-ph↗
arXiv2013

Transition between soft physics at LHC and low-x physics at HERA

We find out the connection between the unintegrated gluon distribution at low intrinsic transverse momenta and the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. The parameters of this distribution are found from the best description of the LHC data. Its application to the analysis of ep deep inelastic scattering allows us to obtain the results which reasonable describe the H1 and ZEUS data on the structure functions at low x. The connection between the soft processes at LHC and small-x physics at HERA is found.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
arXiv2012

Unintegrated gluon distribution and soft pp collisions at LHC

We found the parameterization of the unintegrated gluon distribution from the best description of the LHC data on the inclusive spectra of hadrons produced in $pp$ collisions at the mid-rapidity region and small transverse momenta. It is different from the one obtained within perturbative QCD only at low intrinsic transverse momenta $k_t$. The application of this distribution to analysis of the $e-p$ DIS allows us to get the results which do not contradict the H1 and ZEUS data on the structure functions at low $x$. So, the connection between the soft processes at LHC and low-$x$ physics at HERA is found.

hep-ph↗