93 research outputs found
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Measurement of the [Formula: see text] production cross section using events in the [Formula: see text] final state in pp collisions at [Formula: see text].
The cross section of top quark-antiquark pair production in proton-proton collisions at [Formula: see text] is measured by the CMS experiment at the LHC, using data corresponding to an integrated luminosity of 2.2[Formula: see text]. The measurement is performed by analyzing events in which the final state includes one electron, one muon, and two or more jets, at least one of which is identified as originating from hadronization of a b quark. The measured cross section is [Formula: see text], in agreement with the expectation from the standard model
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Measurement of the W+W- cross section in pp collisions at √s= 8 TeVand limits on anomalous gauge couplings
A measurement of the W boson pair production cross section in proton-proton collisions at √s = 8 TeV is presented. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 19.4fb-1. The W +W - candidates are selected from events with two charged leptons, electrons or muons, and large missing transverse energy. The measured W +W - cross section is 60.1 ± 0.9 (stat) ± 3.2 (exp) ± 3.1 (theo) ± 1.6 (lumi) pb = 60.1±4.8 pb, consistent with the standard model prediction. The W +W - cross sections are also measured in two different fiducial phase space regions. The normalized differential cross section is measured as a function of kinematic variables of the final-state charged leptons and compared with several perturbative QCD predictions. Limits on anomalous gauge couplings associated with dimension-six operators are also given in the framework of an effective field theory. The corresponding 95 % confidence level intervals are -5.7<cWWW/Λ2<5.9TeV-2, -11.4<cW/Λ2<5.4TeV-2, -29.2<cB/Λ2<23.9TeV-2, in the HISZ basis
Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton–proton collisions at √s = 8 TeV
A search for narrow resonances decaying to an electron and a muon is presented. The eμ mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7 fb-1 collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected eμ pairs, upper limits are set at 95 % confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of τ sneutrino in R-parity violating supersymmetry is considered. The τ sneutrino is excluded for masses below 1.28 TeV for couplings λ132= λ231= λ311′= 0.01 , and below 2.30 TeV for λ132= λ231= 0.07 and λ311′= 0.11. These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the Z boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton’s constant, the search for non-resonant contributions to the eμ mass spectrum excludes QBH production below a threshold mass Mth of 1.99 TeV. In models that invoke extra dimensions, the bounds range from 2.36 TeV for one extra dimension to 3.63 TeV for six extra dimensions. This is the first search for QBHs decaying into the eμ final state.We acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFWand FWF (Austria); FNRS and FWO (Belgium); CNPq,
CAPES, FAPERJ, and FAPESP (Brazil);MES (Bulgaria);CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); MoER, ERC IUT and ERDF (Estonia);
Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland);
INFN (Italy);MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico);MBIE(NewZealand); PAEC(Pakistan);MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS and RFBR (Russia);MESTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF
(USA). Individuals have received support from the Marie-Curie programme and the European Research Council and EPLANET (European Union); the Leventis Foundation; the A. P. Sloan Foundation; the
Alexander von Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie doorWetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Council of Science and Industrial Research, India; the HOMING PLUS programme
of the Foundation for Polish Science, cofinanced from European Union, RegionalDevelopment Fund; the Mobility Plus programme of the Ministry of Science and Higher Education (Poland); the OPUS
programme of the National Science Center (Poland); MIUR project 20108T4XTM (Italy); the Thalis and Aristeia programmes cofinanced by EU-ESF and the Greek NSRF; the National Priorities Research Program
by QatarNationalResearch Fund; theRachadapisek Sompot Fund for Postdoctoral Fellowship, Chulalongkorn University (Thailand); the Chulalongkorn Academic into Its 2nd Century Project Advancement
Project (Thailand); and the Welch Foundation, contract C-1845
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Measurement of the t t ¯ production cross section using events in the e μ final state in pp collisions at √s=13 TeV
© 2017, CERN for the benefit of the CMS collaboration.The cross section of top quark–antiquark pair production in proton–proton collisions at s=13TeV is measured by the CMS experiment at the LHC, using data corresponding to an integrated luminosity of 2.2fb-1. The measurement is performed by analyzing events in which the final state includes one electron, one muon, and two or more jets, at least one of which is identified as originating from hadronization of a b quark. The measured cross section is 815±9(stat)±38(syst)±19(lumi) pb, in agreement with the expectation from the standard model
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Forward–backward asymmetry of Drell–Yan lepton pairs in pp collisions at √s = 8 TeV
© 2016, CERN for the benefit of the CMS collaboration.A measurement of the forward–backward asymmetry AFB of oppositely charged lepton pairs (μμ and ee) produced via Z / γ∗ boson exchange in pp collisions at √s = 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.7 fb-1 collected with the CMS detector at the LHC. The measurement of AFB is performed for dilepton masses between 40 GeV and 2TeV and for dilepton rapidity up to 5. The AFB measurements as a function of dilepton mass and rapidity are compared with the standard model predictions
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Search for direct pair production of scalar top quarks in the single- and dilepton channels in proton-proton collisions at √s= 8 TeV
Results: are reported from a search for the top squark t ˜ 1, the lighter of the two supersymmetric partners of the top quark. The data sample corresponds to 19.7 fb−1 of proton-proton collisions at s=8 TeV collected with the CMS detector at the LHC. The search targets t˜1→bχ˜1± and t˜1→t(∗)χ˜10 decay modes, where χ˜1± and χ˜10 are the lightest chargino and neutralino, respectively. The reconstructed final state consists of jets, b jets, missing transverse energy, and either one or two leptons. Leading backgrounds are determined from data. No significant excess in data is observed above the expectation from standard model processes. The results exclude a region of the two-dimensional plane of possible t ˜ 1 and χ˜10 masses. The highest excluded t ˜ 1 and χ˜10 masses are about 700 GeV and 250 GeV, respectively.[Figure not available: see fulltext.
Nietzsches gelijk: Waarom wijsheid achteraf onbillijk is
A search is performed for a massive new vector-like quark T, with charge 2/3, that is pair produced together with its antiparticle in proton-proton collisions. The data were collected by the CMS experiment at the Large Hadron Collider in 2012 at sqrt(s) = 8 TeV and correspond to an integrated luminosity of 19.5 inverse femtobarns. The T quark is assumed to decay into three different final states, bW, tZ, and tH. The search is carried out using events with at least one isolated lepton. No deviations from standard model expectations are observed, and lower limits are set on the T quark mass at 95% confidence level. The lower limit lies between 687 and 782 GeV for all possible values of the branching fractions into the three different final states assuming strong production. These limits are the most stringent constraints to date on the existence of such a quark
Measurement of the Zγ production cross section in pp collisions at 8 TeV and search for anomalous triple gauge boson couplings
Open Access, Copyright CERN, for the benefit of the CMS Collaboration. Article funded by SCOAP3.Abstract: The cross section for the production of Zγ in proton-proton collisions at 8 TeV is measured based on data collected by the CMS experiment at the LHC corresponding to an integrated luminosity of 19.5 fb−1. Events with an oppositely-charged pair of muons or electrons together with an isolated photon are selected. The differential cross section as a function of the photon transverse momentum is measured inclusively and exclusively, where the exclusive selection applies a veto on central jets. The observed cross sections are compatible with the expectations of next-to-next-to-leading-order quantum chromodynamics. Limits on anomalous triple gauge couplings of ZZγ and Zγγ are set that improve on previous experimental results obtained with the charged lepton decay modes of the Z boson
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Combined search for electroweak production of charginos and neutralinos in proton-proton collisions at √s=13 TeV
A statistical combination of several searches for the electroweak production of charginos and neutralinos is presented. All searches use proton-proton collision data at s=13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb−1. In addition to the combination of previous searches, a targeted analysis requiring three or more charged leptons (electrons or muons) is presented, focusing on the challenging scenario in which the difference in mass between the two least massive neutralinos is approximately equal to the mass of the Z boson. The results are interpreted in simplified models of chargino-neutralino or neutralino pair production. For chargino-neutralino production, in the case when the lightest neutralino is massless, the combination yields an observed (expected) limit at the 95% confidence level on the chargino mass of up to 650 (570) GeV, improving upon the individual analysis limits by up to 40 GeV. If the mass difference between the two least massive neutralinos is approximately equal to the mass of the Z boson in the chargino-neutralino model, the targeted search requiring three or more leptons obtains observed and expected exclusion limits of around 225 GeV on the second neutralino mass and 125 GeV on the lightest neutralino mass, improving the observed limit by about 60 GeV in both masses compared to the previous CMS result. In the neutralino pair production model, the combined observed (expected) exclusion limit on the neutralino mass extends up to 650–750 (550–750) GeV, depending on the branching fraction assumed. This extends the observed exclusion achieved in the individual analyses by up to 200 GeV. The combined result additionally excludes some intermediate gaps in the mass coverage of the individual analyses.[Figure not available: see fulltext.
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