Mesons In Proton-proton Collisions Research Articles

Recombination mechanism for D0-meson production and [formula omitted] production asymmetry in the LHCb p+20Ne fixed-target experiment

We discuss production of neutral D mesons in proton-proton collisions at the LHC (fixed target mode) in the framework of the BJM recombination model. We present rapidity and transverse momentum distributions of D mesons and compare the recombination contribution to the dominant gluon-gluon fusion mechanism. Both the direct production, as dictated by the matrix element, and fragmentation of the associated c or c¯ are included. The latter mechanism generates D mesons with smaller rapidities than those produced directly. We calculate the D0+D‾0 meson distributions relevant for fixed target p+4He collisions at s = 86.6 GeV as well as for p+20Ne collisions at s = 69 GeV. The recombination component is consistent with the LHCb data and in addition results in production asymmetry. The asymmetries in D0−D0‾ production as a function of rapidity and transverse momentum are shown and the cancellation of terms for direct production and associated c/c¯ fragmentation is discussed.

Central exclusive diffractive production of axial-vector $f_{1}$ mesons in proton-proton collisions

Exclusive production of axial-vector f_{1}(1285)f1(1285) meson in proton-proton collisions via pomeron-pomeron fusion within the tensor-pomeron approach is discussed. Two ways to construct the pomeron-pomeron-f_{1}f1 coupling are presented. We adjust the parameters of our model to the WA102 experimental data and compare with predictions of the Sakai-Sugimoto model. Predictions for LHC experiments are given.

Central exclusive production of axial-vector f1 mesons in proton-proton collisions within the tensor-pomeron approach

We discuss the central exclusive production of f_{1}f1 mesons in proton-proton collisions. The diffractive pomeron-pomeron fusion process within the tensor-pomeron approach is considered. Two ways to construct the pomeron-pomeron-f_{1}f1 coupling are discussed. The theoretical calculation of coupling constants is a challenging problem of nonperturbative QCD. We adjust the parameters of the model to the WA102 experimental data. The total cross section and differential distributions are presented. Predictions for LHC experiments are given. Detailed analysis of the distributions in \phi_{pp}ϕpp the azimuthal angle between the transverse momenta of the outgoing protons can help to check different models and to study real pattern of the absorption effects.

Measurement of prompt open-charm production cross sections in proton-proton collisions at sqrt{s} = 13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13 TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb−1. The differential production cross sections of the D∗±, D±, and D0 left({overline{mathrm{D}}}^0right) mesons are presented in ranges of transverse momentum and pseudorapidity 4 < pT< 100 GeV and |η| < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.

Measurement of J/\u03c8 production cross-sections in pp collisions at sqrt{s} = 5 TeV

The production cross-sections of J/ψ mesons in proton-proton collisions at a centre-of-mass energy of sqrt{s} = 5 TeV are measured using a data sample corresponding to an integrated luminosity of 9.13 ± 0.18 pb−1, collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum, pT, and rapidity, y, and separately for J/ψ mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised J/ψ mesons, the production cross-sections integrated over the kinematic range 0 < pT< 20 GeV/c and 2.0 < y < 4.5 areσpromptJ/ψ=8.154±0.010±0.283μb,σnonpromptJ/ψ=0.820±0.003±0.034μb,\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ {\\displaystyle \\begin{array}{c}{\\sigma}_{\\mathrm{prompt}}\\ J/\\psi =8.154\\pm 0.010\\pm 0.283\\ \\upmu \\mathrm{b},\\\\ {}{\\sigma}_{\\mathrm{nonprompt}}\\ J/\\psi =0.820\\pm 0.003\\pm 0.034\\ \\upmu \\mathrm{b},\\end{array}} $$\\end{document}where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at sqrt{s} = 8 TeV and 13 TeV, and are used to update the measurement of the nuclear modification factor in proton-lead collisions for J/ψ mesons at a centre-of-mass energy per nucleon pair of sqrt{s_{mathrm{NN}}} = 5 TeV. The results are compared with theoretical predictions.

Two-gluon production of ϕ and η′ mesons in proton-proton collisions at high energies

We discuss gluon-gluon mechanisms for production of mesons with hidden strangeness, such as $\eta'$ and $\phi$ meson, in proton-proton collisions at large energies. The $g^* g^* \to \eta'$ and $g^* g^* \to \phi g$ mechanisms are considered only and the corresponding cross sections are calculated in the $k_t$-factorization approach. The $F_{\gamma^* \gamma^* \to \eta'}$ and $F_{g^* g^* \to \eta'}$ form factors are calculated from quark-antiquark $\eta'$ light-cone wave function including quark/antiquark transverse momenta. The result for two-photon transition form factor demonstrates that higher twists may survive even to large photon virtualities. The result is compared with the result of a recent leading-twist NLO analysis which uses phenomenological distribution amplitudes fitted to exclusive production of $\eta'$ in $e^+ e^- \to e^+ e^- \eta'$ reaction. We calculate transverse momentum distributions of both $\eta'$ and $\phi$ mesons in proton-proton collisions for RHIC and LHC energies. The results are compared to experimental data whenever available. The results of the Lund string model are shown for comparison for $\eta'$ production at LHC energies. It seems that the two-gluon fusion is not the dominant mechanism for both $\phi$ and $\eta'$ production, although the situation for $\eta'$, especially at larger energies, is less clear due to lack of experimental data.

Semiexclusive production of vector mesons in proton-proton collisions with electromagnetic dissociation

We calculate distributions of different vector mesons in purely exclusive ($p p \to p p V$) and semi-exclusive ($p p \to p X V$) processes with electromagnetic dissociation of a proton. The cross section for the electromagnetic dissociation is expressed through electromagnetic structure functions of the proton. We include the transverse momentum distribution of initial photons in the associated flux. Contributions of the exclusive and semi-exclusive processes are compared for different vector mesons ($V = \phi, J/\psi, \Upsilon$). We discuss how the relative contribution of the semi-exclusive processes depends on the mass of the vector meson as well as on different kinematical variables of the vector meson ($y$, $p_t$). The ratio of semi-exclusive to exclusive contributions are shown and compared for different mesons in different variables.

Semiexclusive production of vector mesons in proton-proton collisions with electromagnetic dissociation of protons

We discuss the semiexclusive production of vector mesons in protonproton collisions with electromagnetic dissociation of one of the protons. Several differential distribution in missing mass (MX), or single-particle variables related exclusively to the produced vector meson are calculated for pp center-of-mass energies 7 and 13 TeV. The cross sections and some differential distributions are compared to their counterparts for purely exclusive reaction $pp \to pV{\rm{ }}p$. For electromagnetic dissociation the important property is that the $p\gamma^{\bigstar} \to Xp$ transitions are given by the electromagnetic structure function of proton. In our calculations we use different parametrizations of the structure function and discuss how it is constrained by the data on virtual photoabsorption on a proton.

Measurement of \u03d2 production in pp collisions at sqrt{s}=13 TeV

The production cross-sections of ϒ(1S), ϒ(2S) and ϒ(3S) mesons in proton-proton collisions at sqrt{s}=13 TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb−1 recorded by the LHCb experiment in 2015. The ϒ mesons are reconstructed in the decay mode ϒ → μ+μ−. The differential production cross-sections times the dimuon branching fractions are measured as a function of the ϒ transverse momentum, pT, and rapidity, y, over the range 0 < pT< 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at sqrt{s}=8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.

Prompt inclusive production of J/ψ , ψ′ and χc mesons at the LHC in forward directions within the NRQCD kt -factorization approach: Search for the onset of gluon saturation

We discuss prompt production of $J/\ensuremath{\psi}$ mesons in proton-proton collisions at the LHC within the NRQCD ${k}_{t}$-factorization approach using Kimber-Martin-Ryskin (KMR) unintegrated gluon distributions (UGDF). We include both direct color-singlet production ($gg\ensuremath{\rightarrow}J/\ensuremath{\psi}g$) as well as a feed down from ${\ensuremath{\chi}}_{c}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\gamma}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}J/\ensuremath{\psi}X$ decays. The production of the decaying mesons (${\ensuremath{\chi}}_{c}$ or ${\ensuremath{\psi}}^{\ensuremath{'}}$) is also calculated within the NRQCD ${k}_{t}$-factorization approach. The corresponding matrix elements for $gg\ensuremath{\rightarrow}J/\ensuremath{\psi}\text{ }\text{ }\mathrm{g}$, $gg\ensuremath{\rightarrow}{\ensuremath{\psi}}^{\ensuremath{'}}g$ and $gg\ensuremath{\rightarrow}{\ensuremath{\chi}}_{c}$ include parameters of the nonrelativistic space wave functions of the quarkonia at $r=0$, which are taken from potential models in the literature. We get the ratio of the corresponding cross section ratio for ${\ensuremath{\chi}}_{c}(2)$-to-${\ensuremath{\chi}}_{c}(1)$ at midrapidities much closer to experimental data than obtained in a recent analysis. Differential distributions in rapidity and transverse momentum of $J/\ensuremath{\psi}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}$ are calculated and compared with experimental data of the ALICE and LHCb Collaborations. We discuss a possible onset of gluon saturation effects in the production of $J/\ensuremath{\psi}$ and ${\ensuremath{\chi}}_{c}$ mesons at forward/backward rapidities. We show that it is necessary to modify the standard KMR UGDF to describe ALICE and LHCb data. A mixed UGDF scenario was proposed. Then, we can describe the experimental data for $J/\ensuremath{\psi}$ production within model uncertainties with a color-singlet component only. Therefore, our theoretical results leave only relatively small room for the color-octet contributions. We discuss relations to other models in the literature. The results for the so-called hybrid model are compared to the results of the original ${k}_{t}$-factorization approach.

BB¯ angular correlations at the LHC in the parton Reggeization approach merged with higher-order matrix elements

We calculate the angular distribution spectra between beauty ($B$) and anti-beauty ($\bar B$) mesons in proton-proton collisions in the leading order approximation of the parton Reggeization approach consistently merged with the next-to-leading order corrections from the emission of additional hard gluon. To describe b-quark hadronization we use the universal scale-depended parton-to-meson fragmentation functions extracted from the world $e^+e^-$ annihilation data. We have obtained good agreement between our predictions and data from the CMS Collaboration at the energy $\sqrt{S}=7$ TeV for $B \bar B$ angular correlations within uncertainties and without free parameters. Predictions for analogous correlation observables at $\sqrt{S}=13$ TeV are provided.

Angular correlations in pair production at the LHC in the parton Reggeization approach

We calculate angular correlation spectra between beauty ( B ) and anti-beauty B mesons in proton-proton collisions in the leading order approximation of the parton Reggeization approach consistently merged with the next-to-leading order corrections from the emission of additional hard gluon (NLO * approximation). To describe b-quark hadronization we use the universal scale-depended parton-to-meson fragmentation functions extracted from the combined e + e - annihilation data. The Kimber-Martin-Ryskin model for the unintegrated parton distribution functions in a proton is implied. We have obtained good agreement between our predictions and data from the CMS Collaboration at the energy S=7 TeV for B B angular correlations within uncertainties and without free parameters.

Large-pTproduction ofDmesons at the LHCb in the parton Reggeization approach

The production of D mesons in proton-proton collisions at the LHCb detector is studied. We consider the single production of D^0, D^+, D^star, and D_s^+ mesons and correlation spectra in the production of DbarD and DD pairs at the sqrt{S}=7 TeV and sqrt{S}=13 TeV. In case of the single D-meson production we calculate differential cross sections over transverse momentum p_T while in the pair DbarD,DD-meson production the cross sections are calculated over the azimuthal angle difference, rapidity difference, invariant mass of the pair M and over the p_T of the one meson from a pair. The cross sections are obtained at the leading order of the parton Reggeization approach using Kimber-Martin-Ryskin unintegrated parton distribution functions in a proton. To describe the D-meson production we use universal scale-dependent c-quark and gluon fragmentation functions fitted to e^+e^- annihilation data from CERN LEP1. Our predictions find a good agreement with the LHCb Collaboration data within uncertainties and without free parameters.

Photoproduction ofJ/ψand ϒ in exclusive and proton dissociative diffractive events

The amplitude for $\gamma p \to V p$, where $V$ is a $J/\psi$ or $\Upsilon$ ground state or excited vector meson, is calculated in a pQCD $k_{T}$-factorization approach. We use this amplitude to predict the cross section for exclusive photoproduction of $J/\psi, \psi', \Upsilon$ mesons in proton-proton collisions. Calculations are performed for a variety of unintegrated gluon distributions, and we compare our results to LHCb data. Here we especially focus on the possibilty of constraining saturation effects. Compared to earlier calculations we include both Dirac and Pauli electromagnetic form factors. We discuss the role of the $Q\bar Q$ light-cone wave functions for differential distributions for ratios such as $\sigma(\psi')/\sigma(J/\psi)$. Absorption effects are always taken into account. We also discuss the related diffractive production in proton dissociative events. Here we concentrate on electromagnetic dissociation , which is calculable without additional free parameters. Besides being of interest in their own right, dissociative events constitute an important experimental background to exclusive production.

Inclusive production of J/ψandψ′ mesons at the LHC

We discuss the prompt production of $J/\psi$ mesons in proton-proton collisions at the LHC within a NRQCD $k_{t}$-factorization approach using Kimber-Martin-Ryskin (KMR) unintegrated gluon distributions (UGDF). We include both direct color-singlet production ($gg \to J/\psi$g) as well as a feed-down from $\chi_{c} \to J/\psi \gamma$ and $\psi' \to J/\psi X$. The production of the decaying mesons ($\chi_{c}$ or $\psi'$)is also calculated within NRQCD $k_{t}$-factorization. The corresponding matrix elements for $gg \to J/\psi$, $gg \to \psi'$ and $gg \to \chi_{c}$ include parameters of the nonrelativistic spatial wave functions of quarkonia at $r=0$, which are taken from potential models from the literature. We get the ratio of the corresponding of the cross sections for $\chi_{c}(2)$-to-$\chi_{c}(1)$ much closer to experimental data than obtained in recent analyses. Differential distributions in rapidity of $J/\psi$ and $\psi'$ are calculated and compared to experimental data of the ALICE and LHCb collaborations. We discuss possible onset of gluon saturation effects at forward/backward rapidities. One can describe the experimental data for $J/\psi$ production within model uncertainties with color-singlet component only. Therefore our theoretical results leave only a relatively small room for the color-octet contributions.

Measurement of forward J/ψ production cross-sections in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

The production of $J/\psi$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is studied with the \lhcb detector. Cross-section measurements are performed as a function of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/\psi$ meson in the region $p_\mathrm{T}<14\mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/\psi$ mesons and $J/\psi$ mesons from $b$-hadron decays. The production cross-sections integrated over the kinematic coverage are $15.03\pm 0.03\pm 0.94$ $\mu$b for prompt $J/\psi$ and $2.25\pm 0.01\pm 0.14$ $\mu$b for $J/\psi$ from $b$-hadron decays, assuming zero polarization of the $J/\psi$ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for $J/\psi$ mesons from $b$-hadron decays is used to extrapolate to a total $b\bar{b}$ cross-section. The ratios of the cross-sections with respect to $\sqrt{s}=8$ TeV are also determined.

Measurement of Bc+ Production in Proton-Proton Collisions at √[s]=8 TeV.

Production of Bc+ mesons in proton-proton collisions at a center-of-mass energy of 8 TeV is studied with data corresponding to an integrated luminosity of 2.0 fb-1 recorded by the LHCb experiment. The ratio of production cross sections times branching fractions between the Bc+→J/ψπ+ and B+→J/ψK+ decays is measured as a function of transverse momentum and rapidity in the regions 0<pT<20 GeV/c and 2.0<y<4.5. The ratio in this kinematic range is measured to be (0.683±0.018±0.009)%, where the first uncertainty is statistical and the second systematic.

Exclusive photoproduction of charmonia in γp → V p and pp → pV p reactions within kt-factorization approach

The amplitude for $\gamma p \to J/\psi p$ ($\gamma p \to \psi' p$) is calculated in a pQCD $k_{T}$-factorization approach. The total cross section for this process is calculated for different unintegrated gluon distributions and compared with the HERA data and the data extracted recently by the LHCb collaboration. The amplitude for $\gamma p \to J/\psi p$ ($\gamma p \to \psi' p$) is used to predict the cross section for exclusive photoproduction of $J/\psi$ ($\psi'$) meson in proton-proton collisions. Compared to earlier calculations we include both Dirac and Pauli electromagnetic form factors. The effect of Pauli form factor is quantified. Absorption effects are taken into account and their role is discussed in detail. Different differential distributions e.g. in $J/\psi$ ($\psi'$) rapidity and transverse momentum are presented and compared with existing experimental data. The UGDF with nonlinear effects built in better describe recent experimental data of the LHCb collaboration but no definite conclusion on onset of saturation can be drawn. We present our results also for the Tevatron. A good agreement with the CDF experimental data points at the midrapidity for both $J/\psi$ and $\psi'$ is achieved.

Central production of η and η′ via double Pomeron exchange in the Sakai-Sugimoto model

We construct a string-inspired model for the central production of $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ mesons in proton-proton collisions via double Pomeron exchange. Using general symmetry considerations, we construct a low-energy differential cross section for double glueball exchange in terms of some undetermined coupling constants and form factors. We extend this model to the Regge regime, replacing the glueball propagators with Pomeron trajectories and modifying the interaction term by a factor derived from the five-string scattering amplitude in flat space. We then fix the couplings which remain undetermined, using the Sakai--Sugimoto framework to model low-energy QCD. Finally, we generate a simulation of the scattering process at $\sqrt{s}=29.1\text{ }\text{ }\mathrm{GeV}$, where double Pomeron exchange should play a role (secondary to double Reggeon exchange). We focus on the dependence of the scattering cross section on ${\ensuremath{\theta}}_{34}$, the angle between the scattered protons in the transverse plane. The results exhibit a definite deviation from the pure ${\mathrm{sin}}^{2}{\ensuremath{\theta}}_{34}$ dependence that arises as a consequence of natural parity violation alone. The amount of deviation is primarily determined by couplings that come from the Chern--Simons action of the anti-de Sitter/QCD supergravity dual, which is directly related to the QCD gravitational anomaly, and thus constitutes a universal part of any five-dimensional string/gravity dual theory of QCD. We argue that this makes the high-energy central production of pseudoscalar mesons an interesting probe of anti-de Sitter/QCD models.

Study of the NN$\eta '$ Production with COSY-11

We describe a new high precision measurement of the production cross-section for the eta' meson in proton-proton collisions for five beam momenta at low access energy region Q conducted at the COSY-11 detection system together with an updated results of all other previous measurements of cross-section for (pp-->pp eta') at COSY-11.