1,782 research outputs found

    Search for New Physics with a Monojet and Missing Transverse Energy in pp Collisions at √s= 7 TeV

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    A study of events with missing transverse energy and an energetic jet is performed using pp collision data at a center-of-mass energy of 7 TeV. The data were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb-1. An excess of these events over standard model contributions is a signature of new physics such as large extra dimensions and unparticles. The number of observed events is in good agreement with the prediction of the standard model, and significant extension of the current limits on parameters of new physics benchmark models is achieved

    Search for New Physics with a Monojet and Missing Transverse Energy in pp Collisions at √s= 7 TeV

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    A study of events with missing transverse energy and an energetic jet is performed using pp collision data at a center-of-mass energy of 7 TeV. The data were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb-1. An excess of these events over standard model contributions is a signature of new physics such as large extra dimensions and unparticles. The number of observed events is in good agreement with the prediction of the standard model, and significant extension of the current limits on parameters of new physics benchmark models is achieved

    Measurement of the t-Channel Single Top Quark Production Cross Section in pp̅ Collisions at √s= 7 TeV

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    Electroweak production of the top quark is measured for the first time in pp collisions at √s= 7 TeV, using a data set collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb-1. With an event selection optimized for t-channel production, two complementary analyses are performed. The first one exploits the special angular properties of the signal, together with background estimates from the data. The second approach uses a multivariate analysis technique to probe the compatibility with signal topology expected from electroweak top-quark production. The combined measurement of the cross section is 83.6±29.8 (stat + syst) ± 3.3 (lumi) pb, consistent with the standard model expectation

    Measurement of the B0s Production Cross Section with B0s → J/ Decays in pp Collisions at √s = 7 TeV

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    The B0s differential production cross section is measured as functions of the transverse momentum and rapidity in pp collisions at √s= 7 TeV, using the B0s → J/UO decay, and compared with predictions based on perturbative QCD calculations at next-to-leading order. The data sample, collected by the CMS experiment at the LHC, corresponds to an integrated luminosity of 40 pb-1. The B0s is reconstructed from the decays J/U → µ+µ- and O→ K+K- The integrated B0s cross section times B0s→ J/UO branching fraction in the range 8BT\u3c 50 GeV/c and │yB \u3c 2.4 is measured to be 6.9 ± 0.6 ± 0.6 nb, where the first uncertainty is statistical and the second is systematic

    Search for Three-Jet Resonances in pp Collisions at √s= 7 TeV

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    A search for three-jet hadronic resonance production in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb-1. Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed using a signature-based approach. The number of expected standard model background events is found to be in good agreement with the observed events. Limits on the cross section times branching ratio are set in a model of gluino pair production with an R-parity-violating decay to three quarks, and the data rule out such particles within the mass range of 200 to 280 GeV/c2

    Measurement of the Λb cross section and the Λb to Λb ratio with J/ψΛ decays in pp collisions at √s = 7 TeV

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    The Λb differential production cross section and the cross section ratio σ(Λ̅b )/σ(Λb) are measured as functions of transverse momentum pΛbT and rapidity |yΛb | in pp collisions at √ s = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Λb decays reconstructed in the exclusive final state J/ψΛ, with the subsequent decays J/ψ →μ+μ− and Λ→pπ, using a data sample corresponding to an integrated luminosity of 1.9 fb−1. The product σ(Λb) × B(Λb →J/ψΛ) versus pΛbT falls faster than that of b mesons. The measured value of σ(Λb) × B(Λb →J/ψΛ) for pΛbT \u3e 10 GeV and |yΛb | \u3c 2.0 is 1.16±0.06±0.12 nb, and the integrated σ(Λ̅b)/σ(Λb) ratio is 1.02±0.07±0.09, where the uncertainties are statistical and systematic, respectively

    Azimuthal anisotropy of charged particles with transverse momentum up to 100 GeV/\u3ci\u3ec\u3c/i\u3e in PbPb collisions at √sNN = 5.02TeV

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    The Fourier coefficients v2 and v3 characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at √sNN = 5.02TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, 1 \u3c pT \u3c 100 GeV/c. The analysis focuses on the pT \u3e 10 GeV/c range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The v2 coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to pT ∼ 60–80 GeV/c, in all examined centrality classes. The v3 coefficient, only measured with the scalar product method, tends to zero for pT [?] 20 GeV/c. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations

    Search for the pair production of third-generation squarks with two-body decays to a bottom or charm quark and a neutralino in proton–proton collisions at √s=13 TeV

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    Results are presented from a search for the pair production of third-generation squarks in proton–proton collision events with two-body decays to bottom or charm quarks and a neutralino, which produces a significant imbalance in the transverse momentum. The search is performed using a sample of proton–proton collision data at √s=13 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb−1. No statistically significant excess of events is observed beyond the expected contribution from standard model processes. Exclusion limits are set in the context of simplified models of bottom or top squark pair production. Models with bottom squark masses up to 1220 GeV are excluded at 95% confidence level for light neutralinos, and models with top squark masses of 510 GeV are excluded assuming that the mass splitting between the top squark and the neutralino is small

    Search for Higgs boson pair production in events with two bottom quarks and two tau leptons in proton–proton collisions at √s=13 TeV

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    A search for the production of Higgs boson pairs in proton–proton collisions at a centre-of-mass energy of 13 TeV is presented, using a data sample corresponding to an integrated luminosity of 35.9fb−1 collected with the CMS detector at the LHC. Events with one Higgs boson decaying into two bottom quarks and the other decaying into two τ leptons are explored to investigate both resonant and nonresonant production mechanisms. The data are found to be consistent, within uncertainties, with the standard model background predictions. For resonant production, upper limits at the 95% confidence level are set on the production cross section for Higgs boson pairs as a function of the hypothesized resonance mass and are interpreted in the context of the minimal supersymmetric standard model. For nonresonant production, upper limits on the production cross section constrain the parameter space for anomalous Higgs boson couplings. The observed (expected) upper limit at 95% confidence level corresponds to about 30(25) times the prediction of the standard model

    CMS: Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at p [?] = 0.9 and 2.36TeV

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    Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at [?] = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0:46 ± 0:01 (stat.) ± 0.01 (syst.) GeV/c at 0.9 TeV and 0:50 ± 0:01 (stat.) ± 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2:4 and +2:4. At these energies, the measured pseudorapidity densities in the central region, dNch/dn||n|\u3c0.5, are 3.48±0.02 (stat.) ± 0.13 (syst.) and 4.47±0.04 (stat.) ± 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in pp and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date
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