A search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 fb −1 . No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeV at 95% confidence level for a W 0 -boson with the same couplings as that of the standard model W-boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza-Klein W ð2Þ KK states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W-boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W 0 -boson and the standard model W-boson and for a compositeness model.
Single top quark events produced in the t channel are used to set limits on anomalous Wtb couplings and to search for top quark flavour-changing neutral current (FCNC) interactions. The data taken with the CMS detector at the LHC in proton-proton collisions at √ s = 7 and 8 TeV correspond to integrated luminosities of 5.0 and 19.7 fb −1 , respectively. The analysis is performed using events with one muon and two or three jets. A Bayesian neural network technique is used to discriminate between the signal and backgrounds, which are observed to be consistent with the standard model prediction. The 95% confidence level (CL) exclusion limits on anomalous right-handed vector, and left-and righthanded tensor Wtb couplings are measured to be |f R V | < 0.16, |f L T | < 0.057, and −0.049 < f R T < 0.048, respectively. For the FCNC couplings κ tug and κ tcg , the 95% CL upper limits on coupling strengths are |κ tug |/Λ < 4.1 × 10 −3 TeV −1 and |κ tcg |/Λ < 1.where Λ is the scale for new physics, and correspond to upper limits on the branching fractions of 2.0 × 10 −5 and 4.1 × 10 −4 for the decays t → ug and t → cg, respectively. The CMS collaboration 26 IntroductionSingle top quark (t) production provides ways to investigate aspects of top quark physics that cannot be studied with tt events [1]. The theory of electroweak interactions predicts three mechanisms for producing single top quarks in hadron-hadron collisions. At leading order (LO), these are classified according to the virtuality of the W boson propagation in t-channel, s-channel, or associated tW production [2]. Single top quark production in all channels is directly related to the squared modulus of the Cabibbo-Kobayashi-Maskawa matrix element V tb . As a consequence, it provides a direct measurement of this quantity and thereby a check of the standard model (SM Collaborations. There are two complementary strategies to search for FCNC in single top quark production. A search can be performed in the s channel for resonance production through the fusion of a gluon (g) with an up (u) or charm (c) quark, as was the case in analyses by the CDF and ATLAS Collaborations. However, as pointed out by the D0 Collaboration, the s-channel production rate is proportional to the square of the FCNC coupling parameter and is therefore expected to be small [22]. On the other hand, the t-channel cross section and its corresponding kinematic properties have been measured accurately at the LHC [24][25][26], with an important feature being that the t-channel signature contains a light-quark jet produced in association with the single top quark. This light-quark jet can be used to search for deviations from the SM prediction caused by FCNC in the top quark sector. This strategy was applied by the D0 Collaboration [22], as well as in our analysis. Models that have contributions from FCNC in the production of single top quarks can have sizable deviations relative to SM predictions. Processes with FCNC vertices in the decay of the top quark are negligible. In contrast, the ...
A search for a charged Higgs boson is performed with a data sample corresponding to an integrated luminosity of 19.7 ± 0.5 fb −1 collected with the CMS detector in proton-proton collisions at √ s = 8,TeV. The charged Higgs boson is searched for in top quark decays for m H ± < m t − m b , and in the direct production pp → t(b)H ± for m H ± > m t − m b . The H ± → τ ± ν τ and H ± → tb decay modes in the final states τ h +jets, µτ h , +jets, and ' ( =e, µ) are considered in the search. No signal is observed and 95% confidence level upper limits are set on the charged Higgs boson production. A modelindependent upper limit on the product branching fraction B(t → H ± b) B(H ± → τ ± ν τ ) = 1.2-0.15% is obtained in the mass range m H ± = 80-160 GeV, while the upper limit on the cross section times branching fraction σ(pp → t(b)H ± ) B(H ± → τ ± ν τ ) = 0.38-0.025 pb is set in the mass range m H + = 180-600 GeV. Here, σ(pp → t(b)H ± ) stands for the cross section sum σ(pp → t(b)H + ) + σ(pp → t(b)H − ). Assuming B(H ± → tb) = 1, an upper limit on σ(pp → t(b)H ± ) of 2.0-0.13 pb is set for m H ± = 180-600 GeV. The combination of all considered decay modes and final states is used to set exclusion limits in the m H ± -tan β parameter space in different MSSM benchmark scenarios.Keywords: Hadron-Hadron Scattering, Higgs physics, Supersymmetry 9 Systematic uncertainties 20 9.1 Uncertainties common to the analyses 22 9.2 The τ h +jets final state for H + → τ + ν τ 23 9.3 The µτ h final state for H + → τ + ν τ and H + → tb 24 9.4 Dilepton (ee/eµ/µµ) final states for H + → τ + ν τ and H + → tb 26 9.5 Single-lepton (e/µ+jets) final states for H + → tb 27-i - JHEP11(2015)01810 Results 28 10.1 Model-independent limits on charged Higgs boson production (H + → τ + ν τ ) 29 10.2 Limits on charged Higgs boson production with branching fraction assumed 29 10.3 Combined limits on tan β in MSSM benchmark scenarios 31 Summary 34The CMS collaboration 44 IntroductionIn 2012, a neutral boson with a mass of approximately 125 GeV was discovered by the CMS and ATLAS experiments [1][2][3] at the CERN LHC. The properties of the new boson are consistent with those predicted for the standard model (SM) Higgs boson [4][5][6][7][8][9]. Models with an extended Higgs sector are constrained by the measured mass, CP quantum numbers, and production rates of the new boson. The discovery of another scalar boson, neutral or charged, would represent unambiguous evidence for the presence of physics beyond the SM. Charged Higgs bosons are predicted in models including at least two Higgs doublets. The simplest of such models are the two-Higgs-doublet models (2HDM) [10]. Two Higgs doublets result in five physical Higgs bosons: light and heavy CP-even Higgs bosons h and H, a CP-odd Higgs boson A, plus two charged Higgs bosons H ± . Throughout this paper, charge conjugate states are implied, the cross section σ(pp → t(b)H + ) denotes the sum σ(pp → t(b)H + ) + σ(pp → t(b)H − ), and the branching fractions B(H + → X) stand for B(H ± → X). The minimal super...
A search for exclusive or semi-exclusive γγ production, pp → p ( * ) + γγ + p ( * ) (where p * stands for a diffractively-dissociated proton), and the observation of exclusive and semi-exclusive e + e − production, pp → p ( * ) + e + e − + p ( * ) , in proton-proton collisions at √ s = 7 TeV, are presented. The analysis is based on a data sample corresponding to an integrated luminosity of 36 pb −1 recorded by the CMS experiment at the LHC at low instantaneous luminosities. Candidate γγ or e + e − events are selected by requiring the presence of two photons or a positron and an electron, each with transverse energy E T > 5.5 GeV and pseudorapidity |η| < 2.5, and no other particles in the region |η| < 5.2. No exclusive or semi-exclusive diphoton candidates are found in the data. An upper limit on the cross section for the reaction pp → p ( * ) + γγ + p ( * ) , within the above kinematic selections, is set at 1.18 pb at 95% confidence level. Seventeen exclusive or semi-exclusive dielectron candidates are observed, with an estimated background of 0.85 ± 0.28 (stat.) events, in agreement with the QED-based prediction of 16.3 ± 1.3 (syst.) events.
An analysis of dijet events in PbPb and pp collisions is performed to explore the properties of energy loss by partons traveling in a quark-gluon plasma. Data are collected at a nucleon-nucleon center-of-mass energy of 2.76 TeV at the LHC. The distribution of transverse momentum (p T ) surrounding dijet systems is measured by selecting charged particles in different ranges of p T and at different angular cones of pseudorapidity and azimuth. The measurement is performed as a function of centrality of the PbPb collisions, the p T asymmetry of the jets in the dijet pair, and the distance parameter R used in the anti-k T jet clustering algorithm. In events with unbalanced dijets, PbPb collisions show an enhanced multiplicity in the hemisphere of the subleading jet, with the p T imbalance compensated by an excess of low-p T particles at large angles from the jet axes.
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