410 research outputs found

    Design of the TEPX luminometer for the CMS experiment at the HL-LHC

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    Se describe el diseño y el rendimiento esperado para la medición precisa de la luminosidad del detector Tracker Endcap Pixel (TEPX) para el experimento CMS en el próximo High-Luminosity LHC (HL-LHC). El detector TEPX está compuesto por 4 discos dobles de doble cara en cada extremo de CMS que cubren el rango de | z | de 175 a 265 cm, cada disco está formado por 5 anillos compuestos por sensores de silicio, con un total de 800 millones de píxeles distribuidos en los 8 discos. El disco 4, anillo 1 (TEPXD4R1) se dedicará a la luminosidad y las mediciones de fondo inducidas por el haz, utilizando el mismo método que el resto de TEPX, es decir, el conteo de grupos de píxeles. Para el HL-LHC, el objetivo es lograr una incertidumbre final del 1 % para las mediciones de luminosidad offline. Se presenta el rendimiento esperado de los luminómetros TEPX y TEPXD4R1 en términos de precisión estadística para la calibración de barrido de van der Meer y para las condiciones físicas, así como el rendimiento de linealidad de cada disco

    Search for narrow trijet resonances in proton-proton collisions at s\sqrt{s} = 13 TeV

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    International audienceThe first search for narrow resonances decaying to three well-separated hadronic jets is presented. The search uses proton-proton collision data corresponding to an integrated luminosity of 138 fb1^{-1} at s\sqrt{s} = 13 TeV, collected at the CERN LHC. No significant deviations from the background predictions are observed between 1.75-9.00 TeV. The results provide the first mass limits on a right-handed boson ZR_{\mathrm{R}} decaying to three gluons, an excited quark decaying via a vector boson to three quarks, as well as updated limits on a Kaluza-Klein gluon decaying via a radion to three gluons

    Observation of WWγ\gamma production and search for Hγ\gamma production in proton-proton collisions at s\sqrt{s} = 13 TeV

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    International audienceThe observation of WWγ\gamma production in proton-proton collisions at a center-of-mass energy of 13 TeV with an integrated luminosity of 138 fb1^{-1} is presented. The observed (expected) significance is 5.6 (4.7) standard deviations. Events are selected by requiring exactly two leptons (one electron and one muon) of opposite charge, moderate missing transverse momentum, and a photon. The measured fiducial cross section for WWγ\gamma is 6.0 ±\pm 0.8 (stat) ±\pm 0.7 (syst) ±\pm 0.6 (modeling) fb, in agreement with the next-to-leading order quantum chromodynamics prediction. The analysis is extended with a search for the associated production of the Higgs boson and a photon, which is generated by a coupling of the Higgs boson to light quarks. The result is used to constrain the Higgs boson couplings to light quarks

    Search for direct production of GeV-scale resonances decaying to a pair of muons in proton-proton collisions at s\sqrt{s} = 13 TeV

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    International audienceA search for direct production of low-mass dimuon resonances is performed using s\sqrt{s} = 13 TeV proton-proton collision data collected by the CMS experiment during the 2017-2018 operation of the CERN LHC with an integrated luminosity of 96.6 fb1^{-1}. The search exploits a dedicated high-rate trigger stream that records events with two muons with transverse momenta as low as 3 GeV but does not include the full event information. The search is performed by looking for narrow peaks in the dimuon mass spectrum in the ranges of 1.1-2.6 GeV and 4.2-7.9 GeV. No significant excess of events above the expectation from the standard model background is observed. Model-independent limits on production rates of dimuon resonances within the experimental fiducial acceptance are set. Competitive or world's best limits are set at 90% confidence level for a minimal dark photon model and for a scenario with two Higgs doublets and an extra complex scalar singlet (2HDM+S). Values of the squared kinetic mixing coefficient ε2\varepsilon^2 in the dark photon model above 106^{-6} are excluded over most of the mass range of the search. In the 2HDM+S, values of the mixing angle sin(θH)\sin(\theta_\text{H}) above 0.08 are excluded over most of the mass range of the search with a fixed ratio of the Higgs doublets vacuum expectation tanβ\tan\beta = 0.5

    Elliptic anisotropy measurement of the f0_0(980) hadron in proton-lead collisions and evidence for its quark-antiquark composition

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    International audienceDespite the f0_0(980) hadron having been discovered half a century ago, the question about its quark content has not been settled: it might be an ordinary quark-antiquark (qqˉ\mathrm{q\bar{q}}) meson, a tetraquark (qqˉqqˉ\mathrm{q\bar{q}q\bar{q}}) exotic state, a kaon-antikaon (KKˉ\mathrm{K\bar{K}}) molecule, or a quark-antiquark-gluon (qqˉg\mathrm{q\bar{q}g}) hybrid. This paper reports strong evidence that the f0_0(980) state is an ordinary qqˉ\mathrm{q\bar{q}} meson, inferred from the scaling of elliptic anisotropies (v2v_2) with the number of constituent quarks (nqn_\mathrm{q}), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f0_0(980) state is reconstructed via its dominant decay channel f0_0(980) \toπ+π\pi^+\pi^-, in proton-lead collisions recorded by the CMS experiment at the LHC, and its v2v_2 is measured as a function of transverse momentum (pTp_\mathrm{T}). It is found that the nqn_q = 2 (qqˉ\mathrm{q\bar{q}} state) hypothesis is favored over nqn_q = 4 (qqˉqqˉ\mathrm{q\bar{q}q\bar{q}} or KKˉ\mathrm{K\bar{K}} states) by 7.7, 6.3, or 3.1 standard deviations in the pTp_\mathrm{T}<\lt 10, 8, or 6 GeV/cc ranges, respectively, and over nqn_\mathrm{q} = 3 (qqˉg\mathrm{q\bar{q}g} hybrid state) by 3.5 standard deviations in the pTp_\mathrm{T}<\lt 8 GeV/cc range. This result represents the first determination of the quark content of the f0_0(980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates

    Extracting the speed of sound in the strongly interacting matter created in ultrarelativistic lead-lead collisions at the LHC

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    International audienceUltrarelativistic nuclear collisions create a strongly interacting state of hot and dense quark-gluon matter that exhibits a remarkable collective flow behavior with minimal viscous dissipation. To gain deeper insights into its intrinsic nature and fundamental degrees of freedom, we extracted the speed of sound in this medium created using lead-lead (PbPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data were recorded by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 0.607 nb1^{-1}. The measurement is performed by studying the multiplicity dependence of the average transverse momentum of charged particles emitted in head-on PbPb collisions. Our findings reveal that the speed of sound in this matter is nearly half the speed of light, with a squared value of 0.241 ±\pm 0.002 (stat) ±\pm 0.016 (syst) in natural units. The effective medium temperature, estimated using the mean transverse momentum, is 219 ±\pm 8 (syst) MeV. The measured squared speed of sound at this temperature aligns precisely with predictions from lattice quantum chromodynamic (QCD) calculations. This result provides a stringent constraint on the equation of state of the created medium and direct evidence for a deconfined QCD phase being attained in relativistic nuclear collisions

    Measurement of multijet azimuthal correlations and determination of the strong coupling in proton-proton collisions at s\sqrt{s} = 13 TeV

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    International audienceA measurement is presented of a ratio observable that provides a measure of the azimuthal correlations among jets with large transverse momentum pTp_\mathrm{T}. This observable is measured in multijet events over the range of pTp_\mathrm{T} = 360-3170 GeV based on data collected by the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 134 fb1^{-1}. The results are compared with predictions from Monte Carlo parton-shower event generator simulations, as well as with fixed-order perturbative quantum chromodynamics (pQCD) predictions at next-to-leading-order (NLO) accuracy obtained with different parton distribution functions (PDFs) and corrected for nonperturbative and electroweak effects. Data and theory agree within uncertainties. From the comparison of the measured observable with the pQCD prediction obtained with the NNPDF3.1 NLO PDFs, the strong coupling at the Z boson mass scale is αS(mZ)\alpha_\mathrm{S}(m_\mathrm{Z}) = 0.1177 ±\pm 0.0013 (exp) 0.0073+0.0116_{-0.0073}^{+0.0116} (theo) = 0.11770.0074+0.0117_{-0.0074}^{+0.0117}, where the total uncertainty is dominated by the scale dependence of the fixed-order predictions. A test of the running of αS(mZ)\alpha_\mathrm{S}(m_\mathrm{Z}) in the TeV region shows no deviation from the expected NLO pQCD behaviour

    Performance of CMS muon reconstruction from proton-proton to heavy ion collisions

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    International audienceThe performance of muon tracking, identification, triggering, momentum resolution, and momentum scale has been studied with the CMS detector at the LHC using data collected at sNN\sqrt{s_\mathrm{NN}} = 5.02 TeV in proton-proton (pp) and lead-lead (PbPb) collisions in 2017 and 2018, respectively, and at sNN\sqrt{s_\mathrm{NN}} = 8.16 TeV in proton-lead (pPb) collisions in 2016. Muon efficiencies, momentum resolutions, and momentum scales are compared by focusing on how the muon reconstruction performance varies from relatively small occupancy pp collisions to the larger occupancies of pPb collisions and, finally, to the highest track multiplicity PbPb collisions. We find the efficiencies of muon tracking, identification, and triggering to be above 90% throughout most of the track multiplicity range. The momentum resolution and scale are unaffected by the detector occupancy. The excellent muon reconstruction of the CMS detector enables precision studies across all available collision systems
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