Search for Pair-produced Vector-like B Quarks in Proton-proton Collisions at $\sqrt{s}$

Search for Pair-produced Vector-like B Quarks in Proton-proton Collisions at $\sqrt{s}$
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Total Pages: 46
Release: 2015
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A search for the production of a heavy B quark, having electric charge -1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb-1 . The B quark is assumed to be pair-produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quark-antiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the fi- nal states studied. Our statistical combination of these results was performed and upper limits were set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Additionally, lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.

Search for a Heavy Bottom-like Quark in Pp Collisions at Sqrt(s)

Search for a Heavy Bottom-like Quark in Pp Collisions at Sqrt(s)
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Release: 2011
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A search for pair-produced bottom-like quarks in pp collisions at sqrt(s) = 7 TeV is conducted with the CMS experiment at the LHC. The decay b' to tW is considered in this search. The b' b'-bar to tW-̂ t-bar W+̂ process can be identified by the distinctive signature of trileptons and same-sign dileptons. With a data sample corresponding to an integrated luminosity of 34 inverse picobarns, no excess above the standard model background predictions is observed and a b' quark with a mass between 255 and 361 GeV/c2̂ is excluded at the 95% confidence level.

Search for Single Production of Vector-like Quarks Decaying Into a B Quark and a W Boson in Proton-proton Collisions at $\sqrt{s}

Search for Single Production of Vector-like Quarks Decaying Into a B Quark and a W Boson in Proton-proton Collisions at $\sqrt{s}
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Release: 2017
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A search is presented for a heavy vector-like quark, decaying into a b quark and a W boson, which is produced singly in association with a light flavor quark and a b quark. The analysis is performed using a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s} = $ 13 TeV collected at the LHC in 2015. The data set used in the analysis corresponds to an integrated luminosity of 2.3 inverse-femtobarns. The search is carried out using events containing one electron or muon, at least one b-tagged jet with large transverse momentum, at least one jet in the forward region of the detector, and missing transverse momentum. No excess over the standard model prediction is observed. Upper limits are placed on the production cross section of heavy exotic quarks: a T quark with a charge of 2/3, and a Y quark with a charge of -4/3. For Y quarks with coupling of 0.5 and B(Y to bW) = 100%, the observed (expected) lower mass limits are 1.40 (1.0) TeV. This is the most stringent limit to date on the single production of the Y vector-like quark.

Search for a Vectorlike Quark with Charge 2/3 in T+Z Events from Pp Collisions at Sqrt[s]

Search for a Vectorlike Quark with Charge 2/3 in T+Z Events from Pp Collisions at Sqrt[s]
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Release: 2011
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A search for pair-produced heavy vector-like charge-2/3 quarks, T, in pp collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavor-changing-neutral-current decay of a T quark to a top quark and a Z boson are selected by requiring two leptons from the Z-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of 1.14 inverse femtobarns, the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay T to tZ, a T quark with a mass less than 475 GeV/c2̂ is excluded at the 95% confidence level.

Search for Vector-like Charge 2/3 T Quarks in Proton-proton Collisions at $\sqrt{s}$

Search for Vector-like Charge 2/3 T Quarks in Proton-proton Collisions at $\sqrt{s}$
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Total Pages: 48
Release: 2015
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Our search for fermionic top quark partners T of charge 2/3 is presented. The search is carried out in proton-proton collisions corresponding to an integrated luminosity of 19.7 fb-1 collected at a center-of-mass energy of √s = 8 TeV with the CMS detector at the LHC. The T quarks are assumed to be produced strongly in pairs and can decay into tH, tZ, and bW. The search is performed in five exclusive channels: a singlelepton channel, a multilepton channel, two all-hadronic channels optimized either for the bW or the tH decay, and one channel in which the Higgs boson decays into two photons. The results are found to be compatible with the standard model expectations in all the investigated final states. Finally, a statistical combination of these results is performed and lower limits on the T quark mass are set. Depending on the branching fractions, lower mass limits between 720 and 920 GeV at 95% confidence level are found. These are among the strongest limits on vector-like T quarks obtained to date.

Search for Vector-like T Quarks Using Events with Oppositely-charged Lepton Pairs and Jets in Proton-proton Collisions at Centre-of-mass Energy of 13 TeV with CMS Detector

Search for Vector-like T Quarks Using Events with Oppositely-charged Lepton Pairs and Jets in Proton-proton Collisions at Centre-of-mass Energy of 13 TeV with CMS Detector
Author: Dalath Rachitha Asanga Mendis
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Release: 2019
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A search is performed for heavy vector-like top quark partner (T) with electric charge +2/3 by using proton-proton collision events from Large Hadron Collider (LHC) at a centre- of-mass energy of 13 TeV. The data corresponds to an integrated luminosity of 35.9fb−1 collected by the Compact Muon Solenoid (CMS) experiment during 2016. The production of this new hypothetical particle is assumed to be in pairs and strong interaction is responsible for such production mechanism. T quarks can decay to various combinations of third generation quarks and standard model bosons: T → bW, tZ, or tH, and hence the final states consist of pair of opposite-sign leptons consistent with coming from a Z boson and jets. No significant excess has been observed and hence 95% CL upper limits are obtained on TT production cross section by assuming different branching ratios. T quark mass values below 1280 GeV are excluded in case of 100% branching fraction for T → tZ.

Search for Pair-produced Resonances Decaying to Top Quarks and Jets in Proton-proton Collisions at 8 TeV with the CMS Detector at the LHC

Search for Pair-produced Resonances Decaying to Top Quarks and Jets in Proton-proton Collisions at 8 TeV with the CMS Detector at the LHC
Author: Gala Nicolas Kaufman
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Total Pages: 394
Release: 2014
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We present a search for pair production of new physics resonances decaying into a top quark and a light parton in final states with two leptons, interpreting the results in the context of an R-parity violating supersymmetric model. We use 19.5 fb[-]1 of data collected by the CMS experiment at the LHC from proton-proton collisions at s = 8 TeV in 2012. The experimental signature consists of two leptons (e or [MICRO SIGN]), two jets identified as originating from the decay of a b quark, and two jets identified as coming from light flavor quarks or gluons. We reconstruct and analyze potential resonant decays. The dominant standard model background is top quark pair production with additional jets from initialor final-state radiation. We perform an extended unbinned maximum likelihood fit to the transverse momenta of the two leading light jets and the reconstructed resonance mass. The observation is consistent with the standard model expectation, and we set upper limits on the signal cross section for R-parity violating bottom squarks with masses between 250 and 600 GeV. We exclude R-parity violating bottom squark pair production at the 95% confidence level between 250 GeV and 326 GeV.