A search for a narrow, high-mass resonance decaying into Z and Higgs (H) bosons is presented. The final state studied consists of a merged jet pair and a τ pair resulting from the decays of Z and H ...bosons, respectively. The analysis is based on a data sample of proton–proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS experiment in 2012, and corresponding to an integrated luminosity of 19.7 fb−1. In the resonance mass range of interest, which extends from 0.8 to 2.5 TeV, the Z and H bosons are produced with large momenta, which implies that the final products of the two quarks or the two τ leptons must be detected within a small angular interval. From a combination of all possible decay modes of the τ leptons, production cross sections in a range between 0.9 and 27.8 fb are excluded at 95% confidence level, depending on the resonance mass.
The design and performance of the ZEUS micro vertex detector Polini, A.; Brock, I.; Goers, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
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Journal Article
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In order to extend the tracking acceptance, to improve the primary and secondary vertex reconstruction and thus enhancing the tagging capabilities for short lived particles, the ZEUS experiment at ...the HERA Collider at DESY installed a silicon strip vertex detector. The barrel part of the detector is a 63
cm long cylinder with silicon sensors arranged around an elliptical beampipe. The forward part consists of four circular shaped disks. In total just over 200k channels are read out using
2.9
m
2
of silicon. In this report a detailed overview of the design and construction of the detector is given and the performance of the completed system is reviewed.
The operation of the CMS computing system requires a complex monitoring system to cover all its aspects: central services, databases, the distributed computing infrastructure, production and analysis ...workflows, the global overview of the CMS computing activities and the related historical information. Several tools are available to provide this information, developed both inside and outside of the collaboration and often used in common with other experiments. Despite the fact that the current monitoring allowed CMS to successfully perform its computing operations, an evolution of the system is clearly required, to adapt to the recent changes in the data and workload management tools and models and to address some shortcomings that make its usage less than optimal. Therefore, a recent and ongoing coordinated effort was started in CMS, aiming at improving the entire monitoring system by identifying its weaknesses and the new requirements from the stakeholders, rationalise and streamline existing components and drive future software development. This contribution gives a complete overview of the CMS monitoring system and a description of all the recent activities that have been started with the goal of providing a more integrated, modern and functional global monitoring system for computing operations.
A search is reported for a light pseudoscalar Higgs boson decaying to a pair of τ leptons, produced in association with a bb‾ pair, in the context of two-Higgs-doublet models. The results are based ...on pp collision data at a centre-of-mass energy of 8 TeV collected by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7 fb−1. Pseudoscalar boson masses between 25 and 80 GeV are probed. No evidence for a pseudoscalar boson is found and upper limits are set on the product of cross section and branching fraction to τ pairs between 7 and 39 pb at the 95% confidence level. This excludes pseudoscalar A bosons with masses between 25 and 80 GeV, with SM-like Higgs boson negative couplings to down-type fermions, produced in association with bb‾ pairs, in Type II, two-Higgs-doublet models.
Results are presented from a search for supersymmetric particles in scenarios with small mass splittings. The data sample corresponds to 19.7 fb−1 of proton–proton collisions recorded by the CMS ...experiment at s=8 TeV. The search targets top squark (t˜) pair production in scenarios with mass differences Δm=m(t˜)−m(χ˜10) below the W-boson mass and with top-squark decays in the four-body mode (t˜→bℓνχ˜10), where the neutralino (χ˜10) is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pT) jet associated with initial-state radiation, one or two low-pT leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the t˜ and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for Δm=25 GeV at 95% CL. The dilepton data are also interpreted under the assumption of chargino–neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common χ˜1+/χ˜20 mass and the LSP mass of 20 GeV and a τ-enriched decay scenario, masses in the range m(χ˜1+)<307 GeV are excluded at 95% CL.
Differential cross sections as a function of transverse momentum pT are presented for the production of ϒ(nS) (n = 1, 2, 3) states decaying into a pair of muons. Data corresponding to an integrated ...luminosity of 4.9fb−1 in pp collisions at s=7TeV were collected with the CMS detector at the LHC. The analysis selects events with dimuon rapidity |y|<1.2 and dimuon transverse momentum in the range 10<pT<100GeV. The measurements show a transition from an exponential to a power-law behavior at pT≈20GeV for the three ϒ states. Above that transition, the ϒ(3S) spectrum is significantly harder than that of the ϒ(1S). The ratios of the ϒ(3S) and ϒ(2S) differential cross sections to the ϒ(1S) cross section show a rise as pT increases at low pT, then become flatter at higher pT.
A search is presented for a standard model-like Higgs boson decaying to the μ+μ− or e+e− final states based on proton–proton collisions recorded by the CMS experiment at the CERN LHC. The data ...correspond to integrated luminosities of 5.0 fb−1 at a centre-of-mass energy of 7 TeV and 19.7 fb−1 at 8 TeV for the μ+μ− search, and of 19.7 fb−1 at 8 TeV for the e+e− search. Upper limits on the production cross section times branching fraction at the 95% confidence level are reported for Higgs boson masses in the range from 120 to 150 GeV. For a Higgs boson with a mass of 125 GeV decaying to μ+μ−, the observed (expected) upper limit on the production rate is found to be 7.4 (6.5−1.9+2.8) times the standard model value. This corresponds to an upper limit on the branching fraction of 0.0016. Similarly, for e+e−, an upper limit of 0.0019 is placed on the branching fraction, which is ≈3.7×105 times the standard model value. These results, together with recent evidence of the 125 GeV boson coupling to τ-leptons with a larger branching fraction consistent with the standard model, confirm that the leptonic couplings of the new boson are not flavour-universal.
The consistency of the spin correlation strength in top quark pair production with the standard model (SM) prediction is tested in the muon+jets final state. The events are selected from pp ...collisions, collected by the CMS detector, at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The data are compared with the expectation for the spin correlation predicted by the SM and with the expectation of no correlation. Using a template fit method, the fraction of events that show SM spin correlations is measured to be 0.72±0.08(stat)−0.13+0.15(syst), representing the most precise measurement of this quantity in the muon+jets final state to date.
The tt¯ charge asymmetry is measured in proton–proton collisions at a centre-of-mass energy of 8 TeV. The data, collected with the CMS experiment at the LHC, correspond to an integrated luminosity of ...19.7 fb−1. Selected events contain an electron or a muon and four or more jets, where at least one jet is identified as originating from b-quark hadronization. The inclusive charge asymmetry is found to be 0.0010±0.0068 (stat)±0.0037 (syst). In addition, differential charge asymmetries as a function of rapidity, transverse momentum, and invariant mass of the tt¯ system are studied. For the first time at the LHC, the measurements are also performed in a reduced fiducial phase space of top quark pair production, with an integrated result of −0.0035±0.0072 (stat)±0.0031 (syst). All measurements are consistent within two standard deviations with zero asymmetry as well as with the predictions of the standard model.
A search is performed in proton–proton collisions at s=8TeV for exotic particles decaying via WZ to fully leptonic final states with electrons, muons, and neutrinos. The data set corresponds to an ...integrated luminosity of 19.5 fb−1. No significant excess is observed above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of a W′ boson as predicted by an extended gauge model, and on the W′WZ coupling. The expected and observed mass limits for a W′ boson, as predicted by this model, are 1.55 and 1.47 TeV, respectively. Stringent limits are also set in the context of low-scale technicolor models under a range of assumptions for the model parameters.
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