Search

We calculate the cross sections of associated $J/\psi + \psi^\prime$ and $J/\psi + J/\psi$ 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 $J/\psi + J/\psi$ production and first experimental data on $J/\psi + \psi^\prime$ 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 $\sigma_{\rm eff}$ parameter. The relative production rate $\sigma(J/\psi + \psi^\prime)/\sigma(J/\psi + J/\psi)$ is found to be sensitive to the DPS terms as well as to feeddown contributions.

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., Comment: 9 pages, 2 figures, 1 table

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., Comment: 9 pages, 2 figures

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., Comment: 13 pages, 3 figures, 1 table

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 $\chi_c$ 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 $\chi_{c1}$ and $\chi_{c2}$ states. The extracted values of long-distance matrix elements are employed to analyse the $\chi_c$ 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., Comment: 23 pages, 11 figures, 1 table

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 $J/\psi$ 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) $J/\psi$ production. At the same time, in the region of high enough transverse momenta the nuclear modification factor for associated $J/\psi+W$ production converges to that of unassociated $J/\psi$., Comment: 4 pages, 1 figure; Sec.II has been rewritten in a more clear manner; results are unchanged; matches journal version

The low-x behavior of the linearly polarized gluon density h_{g}(x,k_t^2, Q^2) in nuclei is studied in the rescaling model at small transverse momentum k_t., Comment: 7 pages, 1 figure

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., Comment: 6 pages, 4 figures

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., Comment: 12 pages, 6 figures

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., Comment: 16 pages, 8 figures

We give predictions for the ratio RQ(x,Q2)=FLQ(x,Q2)/F2Q(x,Q2) at small values of Bjorken variable x in the first three orders of perturbation theory. We show an approximate x-independence of RQ(x,Q2) at low x and non-large Q2 values (Q2 < 8--10 m2Q), irrespectively on the gluon density in a proton used in the calculations. This observation could be useful in subsequent phenomenological studies of the heavy flavor production at future lepton-hadron and hadron-hadron colliders., Comment: 10 pages, 3 figures

The behavior of the gluon density in nuclei is investigated in the framework of the rescaling model., Comment: 6 pages, 1 figure

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 $\sigma_{\rm red}^{c}(x,Q^2)$ and $\sigma_{\rm red}^{b}(x,Q^2)$. 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 $\chi^2/d.o.f. = 2.2$, 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., Comment: 26 pages, 11 figures

A new type of parametrization for parton distribution functions in a proton, based on their $Q^2$-evolution at large and small $x$ values, is constructed. In our analysis, the valence and nonsinglet parts obey the Gross-Llewellyn-Smith and Gottfried sum rules, respectively. For the singlet quark and gluon densities momentum conservation is taken into account. Then, using the Kimber-Martin-Ryskin prescription, we extend the consideration to Transverse Momentum Dependent (TMD, or unintegrated) gluon and quark distributions in a proton, which currently plays an important role in a number of phenomenological applications. The analytical expressions for the latter, valid for both low and large $x$, are derived for the first time., Comment: 28 pages, 8 figures

We consider the process of double $J/\psi$ production in $pp$ collisions at the LHC in the framework of $k_T$-factorization approach. We focus on the gluon fragmentation mechanism which is related to multiple gluon emission in the initial state. The initial state emission is treated according to Catani-Ciafaloni-Fiorani-Marchesini evolution equation, and applies to both single and double parton scattering cases. We show the importance of fragmentation contributions to $J/\psi$ pair production and perform a comparison between theoretical predictions and the latest ATLAS data collected at $\sqrt{s} = 8$ TeV. We find that the effects of multiple gluon emission are essential for both single- and multiparton interaction processes. Finally, we highlight the problem of correct choice of the factorization scale with respect to numerical stability of the calculations and the consistency with non-collinear evolution equations.

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., Comment: 15 pages, 5 figures

We reconsider the associated $Z$ boson and charm or beauty jet production at the LHC with paying special attention to the formation dynamics of heavy jets. Two different approaches are studied: first one, where heavy quarks are produced in the hard scattering subprocesses, implemented in the Monte-Carlo generator PEGASUS, and another scenario, where the hard scattering is calculated at NLO with MadGraph5_aMC@NLO and TMD parton shower is included (implemented in the Monte-Carlo generator CASCADE3). We compare the predictions obtained in both schemes with latest experimental data for associated $Z + b$ production cross sections and the relative production rate $\sigma(Z + c)/\sigma(Z + b)$ collected by the ATLAS and CMS Collaborations at $\sqrt s = 13$~TeV. We introduce two kinematic observables (denoted as $z_b$ and $p_T^{\rm rel}$) which can be used to discriminate the heavy jet production mechanisms. Using these variables we trace the shape of the simulated $b$-jet events and recommend that these observables be taken into consideration in the forthcoming experimental analyses., Comment: 11 pages, 4 figures

We consider the production of electroweak $Z$ or $W^\pm$ bosons associated with $J/\psi$ mesons at the LHC conditions. Our attention is focused on new partonic subprocesses which yet have never been considered in the literature, namely, the charmed or strange quark excitation subprocesses followed by the charmed quark fragmentation $c\to J/\psi+c$. Additionally we take into account the effects of multiple quark and gluon radiation in the initial and final states. We find that the contributions from the new mechanisms are important and significantly reduce the gap between the theoretical and experimental results on the $J/\psi + Z$ and $J/\psi + W^\pm$ production cross sections., Comment: 11 pages, 4 figures

To study the heavy quark production processes, we use the transverse momentum dependent (TMD, or unintegrated) gluon distribution function in a proton obtained recently using the Kimber-Martin-Ryskin prescription from the Bessel-inspired behavior of parton densities at small Bjorken $x$ values. We obtained a good agreement of our results with the latest HERA experimental data for reduced cross sections $\sigma^{c\overline{c}}_{\rm red}(x,Q^2)$ and $\sigma^{b\overline{b}}_{\rm red}(x,Q^2)$, and also for deep inelastic structure functions $F_2^c(x,Q^2)$ and $F_2^b(x,Q^2)$ in a wide range of $x$ and $Q^2$ values. Comparisons with the predictions based on the Ciafaloni-Catani-Fiorani-Marchesini evolution equation and with the results of conventional pQCD calculations performed at first three orders of perturbative expansion are presented., Comment: 28 pages, 5 figures

The $\Upsilon(1S)$ meson production and polarization at high energies is studied in the framework of the $k_T$-factorization approach. Our consideration is based on the non-relativistic QCD formalism for a bound states formation and off-shell production amplitudes for hard partonic subprocesses. The direct production mechanism, feed-down contributions from radiative $\chi_b(mP)$ decays and contributions from $\Upsilon(3S)$ and $\Upsilon(2S)$ decays are taken into account. The transverse momentum dependent (TMD) gluon densities in a proton were derived from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation and the Kimber-Martin-Ryskin prescription. Treating the non-perturbative color octet transitions in terms of multipole radiation theory, we extract the corresponding non-perturbative matrix elements for $\Upsilon(1S)$ and $\chi_b(1P)$ mesons from a combined fit to transverse momenta distributions measured at various LHC experiments. Then we apply the extracted values to investigate the polarization parameters $\lambda_\theta$, $\lambda_\phi$ and $\lambda_{\theta\phi}$, which determine the $\Upsilon(1S)$ spin density matrix. Our predictions have a reasonably good agreement with the currently available Tevatron and LHC data within the theoretical and experimental uncertainties., Comment: 28 pages, 14 figures

We consider the associated production of Higgs boson and hadronic jet(s) in $pp$ collisions at the LHC for the first time using the $k_T$-factorization approach. Our analysis is based on the off-shell gluon-gluon fusion subprocess, where non-zero transverse momenta of initial gluons are taken into account and covers $H \to \gamma \gamma$, $H \to ZZ^* \to 4l$ (with $l = e,\mu$) and $H \to W^+ W^- \to e^\pm \mu^\mp \nu \bar \nu$ decay channels. The transverse momentum dependent (TMD) gluon densities in a proton are taken from Catani-Ciafaloni-Fiorani-Marchesini evolution equation. To simulate the kinematics of the produced jets the TMD parton shower implemented into the Monte-Carlo event generator \textsc{cascade} is applied. The comparison of our results with the latest experimental data taken by the CMS and ATLAS Collaborations at $\sqrt s = 8$ and $13$ TeV and conventional higher-order perturbative QCD calculations is presented. We highlight observables, which are sensitive to the TMD gluon densities in a proton., Comment: 14 pages, 6 figures

We consider the prompt double $J/\psi$ production in $pp$ collisions at the LHC in the framework of $k_T$-factorization QCD approach. Using the fragmentation mechanism, we evaluate the color octet contributions to the production cross sections taking into account the combinatorial effects of multiple gluon radiation in the initial state driven by the Ciafaloni-Catani-Fiorani-Marchesini evolution equation. We demonstrate the importance of these contributions in a certain kinematical region covered by the CMS and ATLAS measurements. On the other hand, the experimental data taken by the LHCb Collaboration at forward rapidities and moderate transverse momenta can be described well by ${\cal O}(\alpha_s^4)$ color singlet terms and contributions from the double parton scattering mechanism. The extracted value of the effective cross section $\sigma_{\rm eff} = 17.5 \pm 4.1$~mb is compatible with many other estimations based on different final states., Comment: 18 pages, 10 figures

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., Comment: 80 pages, 32 figures. review article

We analyze the first LHC data on $\chi_{c1}$ and $\chi_{c2}$ polarization obtained very recently by the CMS Collaboration at $\sqrt s = 8$~TeV. We describe the perturbative production of $c\bar c$ pair with $k_T$-factorization approach and use nonrelativistic QCD formalism for the formation of bound states. We demonstrate that the polar anisotropy of $\chi_{c1}$ and $\chi_{c2}$ mesons is strongly sensitive to the color octet contributions. We extract the long-distance matrix elements for $\chi_{c1}$ and $\chi_{c2}$ mesons from the first CMS polarization measurement %on the polarization parameters $\lambda_{\theta}^{\chi_{c1}}$ and $\lambda_{\theta}^{\chi_{c2}}$ obtained at $\sqrt s = 8$~TeV together with available LHC data on the $\chi_{c1}$ and $\chi_{c2}$ transverse momentum distributions (and their ratios) collected at $\sqrt s = 7$~TeV. Our fit points to unequal color singlet wave functions of $\chi_{c1}$ and $\chi_{c2}$ states., Comment: 12 pages, 5 figures, 1 table

PEGASUS is a parton-level Monte-Carlo event generator designed to calculate cross sections for a wide range of hard QCD processes at high energy $pp$ and $p\bar p$ collisions, which incorporates the dynamics of transverse momentum dependent (TMD) parton distributions in a proton. Being supplemented with off-shell production amplitudes for a number of partonic subprocesses and provided with necessary TMD gluon density functions, it produces weighted or unweighted event records which can be saved as a plain data file or a file in a commonly used Les Houches Event format. A distinctive feature of PEGASUS is an intuitive and extremely user friendly interface, allowing one to easily implement various kinematical cuts into the calculations. Results can be also presented "on the fly" with built-in tool \textsc{pegasus plotter}. A short theoretical basis is presented and detailed program description is given., Comment: 24 pages, 8 figures

We use the Bessel-inspired behavior of parton densities at small Bjorken $x$ values, obtained in the case of the flat initial conditions for DGLAP evolution equations in the double scaling QCD approximation (DAS), to evaluate the transverse momentum dependent (TMD, or unintegrated) quark and gluon distribution functions in a proton. The calculations are performed analytically using the Kimber-Martin-Ryskin (KMR) prescription with different implementation of kinematical constraint, reflecting the angular and strong ordering conditions. The relations between the differential and integral formulation of the KMR approach is discussed. Several phenomenological applications of the proposed TMD parton densities to the LHC processes are given., Comment: 24 pages, 9 figures

We consider the associated production of electroweak gauge bosons and charm or beauty quark jets at the LHC using the $k_T$-factorization framework. We apply the transverse momentum dependent (TMD) parton distributions in a proton obtained from the Parton Branching (PB) method as well as from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. For the PB approach, our prescription merges the standard leading order ${\cal O}(\alpha \alpha_s)$ $k_T$-factorization calculations with several tree-level next-to-leading order ${\cal O}(\alpha \alpha_s^2)$ off-shell production amplitudes. For the CCFM scenario, our consideration is based on the ${\cal O}(\alpha \alpha_s^2)$ off-shell gluon-gluon fusion subprocess $g^* g^* \to Z/W + Q\bar Q$ and some subleading ${\cal O}(\alpha \alpha_s^2)$ subprocesses involving quark interactions, taken into account in conventional (collinear) QCD factorization. We find that the $W + c$ and $Z + b$ cross sections, calculated within the PB and CCFM-based schemes with the proper choice of leading and next-to-leading subprocesses, are in good agreement with each other, thus establishing a correspondence between these two scenarios. A comparison with the latest LHC experimental data is given and the necessity for the proper off-shell treatment of the production amplitudes in determination of the parameters of the TMD parton density is demonstrated., Comment: 15 pages, 8 figures

The $\Upsilon(3S)$ 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 $\chi_b(3P)$ decays, we extract the corresponding non-perturbative matrix elements for $\Upsilon(3S)$ and $\chi_b(3P)$ mesons from a combined fit to $\Upsilon(3S)$ 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 $\Upsilon(3S)$ production and to investigate the polarization parameters $\lambda_\theta$, $\lambda_\phi$ and $\lambda_{\theta\phi}$, %and $\tilde\lambda$, which determine the $\Upsilon(3S)$ spin density matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties., Comment: 28 pages, 10 figures. arXiv admin note: text overlap with arXiv:1906.07182

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 $\mathcal O(\alpha\alpha_s^2)$ off-shell gluon-gluon fusion subprocess $g^*g^*\to \gamma q\bar q$ and several subleading quark-initiated contributions from $\mathcal O(\alpha\alpha_s)$ and $\mathcal O(\alpha\alpha_s^2)$ 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., Comment: 12 pages, 4 figures. arXiv admin note: text overlap with arXiv:1708.07079

We analyze the inclusive prompt production of $\psi^\prime$, $\chi_c$, $J/\psi$ and $\eta_c$ 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 $\lambda_\theta$, $\lambda_\phi$, $\lambda_{\theta \phi}$ and the frame-independent parameter $\lambda^*$ and compare them to the available $\psi^\prime$ and $J/\psi$ 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., Comment: 24 pages, 12 figures. arXiv admin note: text overlap with arXiv:1611.10141

In the framework of the $k_T$-factorization, the prompt production of $\eta_c$ 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 $\eta_c$ and $J/\psi$ 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 $J/\psi$ and $\eta_c$ production at the LHC., Comment: 5 pages, 2 figures, 3 tables

We consider the associated production of $J/\psi$ mesons and muons originating from the $b$-flavored hadron decays and non-prompt double $J/\psi$ 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., Comment: 14 pages, 12 figures

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 $\mu_0 \sim 1 - 2$ 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., Comment: 19 pages, 10 figures

In the framework of perturbative QCD and nonrelativistic bound state formalism, we calculate the production of $B_c$ and $B_c^*$ mesons at the conditions of the CDF and LHCb experiments. We derive first estimations for the $B_c$ wave function from a comparison with the available data., Comment: 3 pages, 1 figure

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., Comment: 18 pages, 7 figures

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., Comment: 6 pages, 4 figures

We consider the production of $J/\psi$ and $\psi(2S)$ 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 $J/\psi$ 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 $J/\psi + Z$ production are estimated and found to be small., Comment: 12 pages, 5 figures

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 ${\cal O}(\alpha\alpha_s^2)$ (where the $Z$ boson further decays into a lepton pair), calculated in the $k_T$-factorization approach, and several subleading ${\cal O}(\alpha \alpha_s^2 )$ and ${\cal O}(\alpha \alpha_s^3 )$ 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., Comment: 13 pages, 5 figures

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 $H \to \gamma \gamma$, $H \to ZZ^* \to 4l$ (where $l = e,\mu$) and $H \to W^+ W^- \to e^\pm \mu^\mp \nu \bar \nu$ 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., Comment: 22 pages, 8 figures

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., Comment: 16 pages, 7 figures

In the framework of $k_T$-factorization approach, the production and polarization of prompt $J/\psi$ 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 $\chi_c$ and $\psi(2S)$ 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 $J/\psi$ transverse momentum distributions and then applied to describe the ATLAS and LHCb data on $J/\psi$ production and polarization at $\sqrt s = 7$, $8$ and $13$ TeV. We perform an estimation of polarization parameters $\lambda_\theta$, $\lambda_\phi$ and $\lambda_{\theta \phi}$ which determine $J/\psi$ 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 $J/\psi$ production at high transverse momenta, that is in qualitative agreement with the LHC data., Comment: 23 pages, 14 figures. arXiv admin note: substantial text overlap with arXiv:1508.05480

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., Comment: 8 pages, 7 figures

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, $\gamma(Z) + c$, and the $\gamma(Z)$ and the $b$-jet production. It is shown that this ratio can be approximately flat or increasing at large $\gamma(Z)$ transverse momenta $p_T$ and their pseudo-rapidities $1.5 < \eta < 2.4$ 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., Comment: 17 pages, 9 figures