132 research outputs found

    Performance of an endcap prototype of the Atlas accordion electromagnetic calorimeter

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    The design and construction of a lead-liquid argon endcap calorimeter prototype using an accordion geometry and conceived as a sector of the inner wheel of the endcap calorimeter of the future ATLAS experiment at the LHC is described. The performance obtained using electron beam data is presented. The main results are an energy resolution with a sampling term below 11%/E(GeV)11\%/\sqrt{E(\rm GeV)} and a small local constant term, a good linearity of the response with the incident energy and a global constant term of 0.8\% over an extended area in the rapidity range of 2.2η2.92.2\eta 2.9. These properties make the design suitable for the ATLAS electromagnetic endcap calorimeter

    Search for anomalous Wtb couplings and flavour-changing neutral currents in t-channel single top quark production in pp collisions at root s=7 and 8 TeV

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    Search for massive resonances decaying in to WW,WZ or ZZ bosons in proton-proton collisions at root s=13 TeV

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    Measurement of the mass of the top quark in decays with a J/ψ meson in pp collisions at 8 TeV

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    A first measurement of the top quark mass in the decay channel t → (W → ℓν) (b → J/ψ + X → μ+μ− + X) is presented. The analysis uses events selected from the proton-proton collisions recorded by the CMS detector at the LHC at a center-of-mass energy of 8 TeV. The data correspond to an integrated luminosity of 19.7 fb−1, with 666 tt ¯ tt¯ and single top quark candidate events containing a reconstructed J/ψ candidate decaying into an oppositely-charged muon pair. The mass of the (J/ψ + ℓ) system, where ℓ is an electron or a muon from W boson decay, is used to extract a top quark mass of 173.5 ± 3.0 (stat) ± 0.9 (syst) GeV

    Search for electroweak production of a vector-like quark decaying to a top quark and a Higgs boson using boosted topologies in fully hadronic final states

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    A search is performed for electroweak production of a vector-like top quark partner T of charge 2/3 in association with a standard model top or bottom quark, using 2.3 fb−1 of proton-proton collision data at √s =13 TeV collected by the CMS experiment at the CERN LHC. The search targets T quarks decaying to a top quark and a Higgs boson in fully hadronic final states. For a T quark with mass above 1 TeV the daughter top quark and Higgs boson are highly Lorentz-boosted and can each appear as a single hadronic jet. Jet substructure and b tagging techniques are used to identify the top quark and Higgs boson jets, and to suppress the standard model backgrounds. An excess of events is searched for in the T quark candidate mass distribution in the data, which is found to be consistent with the expected backgrounds. Upper limits at 95% confidence level are set on the product of the single T quark production cross sections and the branching fraction B(T→tH), and these vary between 0.31 and 0.93 pb for T quark masses in the range 1000-1800 GeV. This is the first search for single electroweak production of a vector-like T quark in fully hadronic final states

    Measurement of prompt and nonprompt J/psi production in pp and pPb collisions at root s(NN)=5.02 TeV

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    Measurements of differential production cross sections for a Z boson in association with jets in pp collisions at root s=8 TeV

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    Measurement of the semileptonic tt¯ + γ production cross section in pp collisions at √s = 8 TeV

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    A measurement of the cross section for top quark-antiquark ( tt¯) pairs produced in association with a photon in proton-proton collisions at √s =8 TeV is presented. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb1. The signal is defined as the production of a tt¯ pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the tt¯ pair, and the cross section is measured relative to the inclusive tt¯ pair production cross section. The fiducial cross section for associated tt¯ pair and photon production is found to be 127 ±27 (stat+syst) fb per semileptonic final state. The measured value is in agreement with the theoretical prediction

    Search for associated production of a Z boson with a single top quark and for tZ flavour-changing interactions in pp collisions at √s=8 TeV

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    A search for the production of a single top quark in association with a Z boson is presented, both to identify the expected standard model process and to search for flavour-changing neutral current interactions. The data sample corresponds to an integrated luminosity of 19.7 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s√=8 TeV. Final states with three leptons (electrons or muons) and at least one jet are investigated. An events yield compatible with tZq standard model production is observed, and the corresponding cross section is measured to be σ(pp → tZq → ℓνbℓ+ℓ−q) = 10− 7+ 8 fb with a significance of 2.4 standard deviations. No presence of flavour-changing neutral current production of tZq is observed. Exclusion limits at 95% confidence level on the branching fractions of a top quark decaying to a Z boson and an up or a charm quark are found to be ℬ(t → Zu) < 0.022% and ℬ(t → Zc) < 0.049%
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