Meson Production In Proton-proton Collisions Research Articles

Observation of triple J/ψ meson production in proton-proton collisions

Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be 272−104+141(stat)±17(syst)fb\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$27{2}_{-104}^{+141}\\,{{{\\rm{(stat)}}}}\\,\\pm 17\\,{{{\\rm{(syst)}}}}\\,{{{\\rm{fb}}}}\\,$$\\end{document}, and compared it to theoretical expectations for triple-J/ψ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double- and triple-parton scattering are the dominant contributions for the measured process.

Observation of triple J/ψ meson production in proton-proton collisions at √ s = 13 TeV

The first observation of the three J/ψ meson production in proton-proton collisions at a center-of-mass energy of 13 TeV in final states with three µ +µ − pairs is reported. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 133 fb−1 . The pp → J/ψ J/ψ J/ψ X process is observed with a significance in excess of five standard deviations. The fiducial cross section for this process is found to be σ(pp → J/ψ J/ψ J/ψ X) = 272+141 −104(stat)±17(syst) fb. The result is compared to theoretical expectations for the production of three J/ψ mesons in single (SPS), double- (DPS), and triple- (TPS) parton scattering processes. Under the most economical assumption of factorization of multiple hard scattering probabilities in terms of SPS cross sections, the measured final state is found to be dominated by DPS and TPS contributions. A value of the associated DPS effective cross section parameter of σeff,DPS = 2.7 +1.4 −1.0 (exp)+1.5 −1.0 (theo) mb, related to the transverse distribution of partons in the proton, is derived.

Measurement of {psi {(2S)}} production cross-sections in proton-proton collisions at sqrt{s} =7 and 13text { TeV}

The cross-sections of psi {(2S)} meson production in proton-proton collisions at sqrt{s} =13text { TeV} are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of 275text { pb} ^{-1} . The production cross-sections for prompt psi {(2S)} mesons and those for psi {(2S)} mesons from b-hadron decays ({psi {(2S)}} text{-from- }{b} ) are determined as functions of the transverse momentum, p_{mathrm {T}}, and the rapidity, y, of the psi {(2S)} meson in the kinematic range 2<p_{mathrm {T}} <20text { GeV/}c and 2.0<y<4.5. The production cross-sections integrated over this kinematic region are σ(promptψ(2S),13TeV)=1.430±0.005(stat)±0.099(syst)μb,σ(ψ(2S)-from-b,13TeV)=0.426±0.002(stat)±0.030(syst)μb.\\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}$$\\begin{aligned} \\begin{aligned}&\\sigma (\\text{ prompt } {\\psi {(2S)}},13\\text { TeV})\\\\&\\quad =1.430\\pm 0.005\\text { (stat)} \\pm 0.099\\text { (syst)} \\,\\upmu \\text {b} ,\\\\&\\sigma ({\\psi {(2S)}} \\text{-from- }{b},13\\text { TeV})\\\\&\\quad =0.426\\pm 0.002\\text { (stat)} \\pm 0.030\\text { (syst)} \\,\\upmu \\text {b} . \\end{aligned} \\end{aligned}$$\\end{document}A new measurement of psi {(2S)} production cross-sections in pp collisions at sqrt{s}=7text { TeV} is also performed using data collected in 2011, corresponding to an integrated luminosity of 614text { pb} ^{-1} . The integrated production cross-sections in the kinematic range 3.5<p_{mathrm {T}} <14text { GeV/}c and 2.0<y<4.5 are σ(promptψ(2S),7TeV)=0.471±0.001(stat)±0.025(syst)μb,σ(ψ(2S)-from-b,7TeV)=0.126±0.001(stat)±0.008(syst)μb.\\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}$$\\begin{aligned} \\begin{aligned}&\\sigma (\\text{ prompt } {\\psi {(2S)}},7\\text { TeV})\\\\&\\quad =0.471\\pm 0.001\\text { (stat)} \\pm 0.025\\text { (syst)} \\,\\upmu \\text {b} ,\\\\&\\sigma ({\\psi {(2S)}} \\text{-from- }{b},7\\text { TeV})\\\\&\\quad =0.126\\pm 0.001\\text { (stat)} \\pm 0.008\\text { (syst)} \\,\\upmu \\text {b} . \\end{aligned} \\end{aligned}$$\\end{document}All results show reasonable agreement with theoretical calculations.

Pi ^{0} and eta meson production in proton-proton collisions at sqrt{s}=8 TeV

An invariant differential cross section measurement of inclusive pi ^{0} and eta meson production at mid-rapidity in pp collisions at sqrt{s}=8 TeV was carried out by the ALICE experiment at the LHC. The spectra of pi ^{0} and eta mesons were measured in transverse momentum ranges of 0.3<p_{ text{ T }} <35 text{ GeV/c } and 0.5<p_{ text{ T }} <35 text{ GeV/c }, respectively. Next-to-leading order perturbative QCD calculations using fragmentation functions DSS14 for the pi ^{0} and AESSS for the eta overestimate the cross sections of both neutral mesons, although such calculations agree with the measured eta /pi ^0 ratio within uncertainties. The results were also compared with PYTHIA 8.2 predictions for which the Monash 2013 tune yields the best agreement with the measured neutral meson spectra. The measurements confirm a universal behavior of the eta /pi ^0 ratio seen for NA27, PHENIX and ALICE data for pp collisions from sqrt{s}=27.5 GeV to sqrt{s}=8 TeV within experimental uncertainties. A relation between the pi ^{0} and eta production cross sections for pp collisions at sqrt{s}=8 TeV is given by m_{ text{ T }} scaling for p_{ text{ T }} >3.5 text{ GeV/c }. However, a deviation from this empirical scaling rule is observed for transverse momenta below p_{ text{ T }} <3.5 text{ GeV/c } in the eta /pi ^0 ratio with a significance of 6.2sigma .

Quarkonium and heavy flavour meson production at 13 TeV at ATLAS

First results of the ATLAS experiment at LHC on quarkonium and heavy flavour meson production in proton-proton collisions at 13 TeV are presented. A brief summary of the results obtained at 7-8 TeV is also reported. Comparison of the data cross sections with various theoretical predictions is discussed.

Close to thresholdη′ meson production in proton-proton collisions at cosy-11

Intensive quest for the eta and eta' bound states is currently ongoing at both theoretical and experimental levels e.g. at COSY, ELSA, GSI, JINR, JPARC, LPI, and MAMI. These studies were already supported by data provided by the COSY-11 collaboration including determination of the total width of the eta' meson. In addition, the first rough estimation of the eta'-N interaction from the excitation function of the cross section for the pp-->pp eta' reaction was also performed. Recent precise measurement in this field from the COSY-11 experiment allows to summarize results on the eta' meson production cross section in proton-proton collisions at COSY-11.

Infrared renormalons and single meson production in proton-proton collisions

In this article, we investigate the contribution of the higher-twist Feynman diagrams to the large-${p}_{T}$ inclusive pion production cross section in proton-proton collisions and present the general formulas for the higher-twist differential cross sections in the case of the running coupling and frozen coupling approaches. The structure of infrared renormalon singularities of the higher-twist subprocess cross section and the resummed expression (the Borel sum) for it are found. We compared the resummed higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section. We obtain, that ratio $R=({\ensuremath{\Sigma}}_{{\ensuremath{\pi}}^{+}}^{\mathrm{HT}}{)}^{\mathrm{res}}/({\ensuremath{\Sigma}}_{{\ensuremath{\pi}}^{+}}^{\mathrm{HT}}{)}^{0}$, for all values of the transverse momentum ${p}_{T}$ of the pion identically equivalent to ratio $r=({\ensuremath{\Delta}}_{\ensuremath{\pi}}^{\mathrm{HT}}{)}^{\mathrm{res}}/({\ensuremath{\Delta}}_{\ensuremath{\pi}}^{\mathrm{HT}}{)}^{0}$. It is shown that the resummed result depends on the choice of the meson wave functions used in calculation. Phenomenological effects of the obtained results are discussed.

Tensor meson production in proton-proton collisions from the color glass condensate

We compute the inclusive cross section of ${f}_{2}$ tensor-meson production in proton-proton collisions at high energy. We use an effective theory inspired from the tensor-meson dominance hypothesis that couples gluons to ${f}_{2}$ mesons. We compute the differential cross section in the ${k}_{\ensuremath{\perp}}$ factorization and in the color glass condensate formalism in the low density regime. We show that the two formalisms are equivalent for this specific observable. Finally, we study the phenomenology of ${f}_{2}$ mesons by comparing theoretical predictions of different parametrizations of the unintegrated gluon distribution function. We find that ${f}_{2}$-meson production is another observable that can be used to put constraints on these distributions.

η′meson production in proton-proton collisions

The pp -> pp eta' reaction is investigated within a relativistic meson-exchange model of hadronic interactions. We explore the role of nucleonic and mesonic, as well as the N* resonance currents, in producing eta' mesons. In order to learn more about the production mechanisms, new measurements in the energy region far from the threshold are required.

Elastic Scattering and Single Meson Production in Proton-Proton Collisions at 2.85 Bev

The Brookhaven National Laboratory twenty-inch liquid hydrogen bubble chamber was exposed to a monoenergetic beam of 2.85-Bev protons, elastically scattered from a carbon target in the internal beam of the Cosmotron. All two-prong events, excluding strange particle events, have been studied by the Yale High-Energy Group. The remaining interactions have been studied by the Brookhaven Bubble Chamber Group. Elastic scattering was found to be mostly pure diffraction scattering at center-of-mass angles up to about thirty-five degrees. Some phase shift and/or tapering of the proton edge was required to fit the data at larger angles. No polarization effects in the proton-carbon scattering were observed using hydrogen as an analyzer of polarized protons. Nucleonic isobar formation in the $T=\frac{3}{2}$, $J=\frac{3}{2}$ state was found to account for a large part of single pion production. High-orbital angular-momentum states were found to be greatly favored in single pion production. The isobar model of Lindenbaum and Sternheimer gave good agreement with the observed nucleon and pion energy spectra. No polarization or alignment effects were observed for the isobar assumed in this model.

LVI. The production of mesons in proton-proton collisions

Summary A method of estimating the cross-sections for meson production in proton-proton collisions near the threshold is outlined, together with detailed calculations for spin zero meson fields under certain simplifying assumptions concerning the nuclear forces. It is found that, for the final continuous neutron-proton system, a low energy for the neutron-proton relative motion is favoured; this, together with a large contribution from transitions to a final bound deuteron, leads to a meson spectrum well peaked at the highest allowed energies in agreement with recent experiments. While the total cross-section is dependent more on the shape and size of the inter-nucleon potential than on the meson type, the spectrum at a given angle and, more particularly, the angular distribution are critically dependent on the parity of the produced meson. Comparison with experiment favours scalar mesons.