Results are reported from a search for the anomalous production of highly boosted Z bosons with large transverse momentum and decaying to the dimuon final state. Such Z bosons may be produced in the ...decays of new heavy particles. The search uses pp collision data at sqrt(s) = 7 TeV, corresponding to an integrated luminosity of 5.0 inverse femtobarns recorded with the CMS detector. The shape of the observed transverse-momentum distribution of Z bosons is consistent with standard-model expectations. Constraints are obtained on models predicting the production of excited quarks decaying via electroweak processes. For excited-quark decays involving only standard-model gauge bosons and coupling strengths, masses of excited quarks below 1.94 TeV are excluded at the 95% confidence level, assuming a compositeness scale equal to the excited-quark mass. For excited-quark production via novel contact interactions, masses below 2.22 TeV are excluded, even if the excited quarks do not couple to gluons.
The W-boson helicity fractions in top-quark decays are measured with ttbar events in the lepton+jets final state, using proton-proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 ...with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 5.0 inverse femtobarns. The measured fractions of longitudinal, left-, and right-handed helicity are F0=0.682 +/- 0.030 (stat.) +/- 0.033 (syst.), FL=0.310 +/- 0.022 (stat.) +/- 0.022 (syst.), and FR= 0.008 +/- 0.012 (stat.) +/- 0.014 (syst.), consistent with the standard model predictions. The measured fractions are used to probe the existence of anomalous Wtb couplings. Exclusion limits on the real components of the anomalous couplings gL, gR are also derived.
A search for supersymmetry in final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The data sample corresponds to an ...integrated luminosity of 4.98 inverse femtobarns collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, alphaT, is used as the main discriminator between events with genuine and misreconstructed missing transverse energy. The search is performed in a signal region that is binned in the scalar sum of the transverse energy of jets and the number of jets identified as originating from a bottom quark. No excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of the constrained minimal supersymmetric extension of the standard model, and also in simplified models, with a special emphasis on compressed spectra and third-generation scenarios.
A measurement is presented of the t t-bar cross section (sigmattbar) in proton-proton collisions at a centre-of-mass energy of 7 TeV, in the all-jet final state that contains at least six jets, two ...of which are tagged as likely originating from b quarks. The data correspond to an integrated luminosity of 3.54 inverse femtobarns, collected with the CMS detector at the LHC. The cross section is determined through an unbinned maximum likelihood fit of contributions from background and t t-bar signal to the reconstructed mass spectrum of t t-bar candidates in the data, in which events are subjected to a kinematic fit assuming a t t-bar to W+ b W- b-bar to 6 jets hypothesis. The measurement yields sigmattbar = 139 +/- 10 (stat.) +/- 26 (syst.) +/- 3 (lum.) pb, a result consistent with those obtained in other t t-bar decay channels, as well as with predictions of the standard model.
A measurement of the Z gamma to nu nu-bar gamma cross section in pp collisions at sqrt(s) = 7 TeV is presented, using data corresponding to an integrated luminosity of 5.0 inverse femtobarns ...collected with the CMS detector. This measurement is based on the observation of events with an imbalance of transverse energy in excess of 130 GeV and a single photon in the absolute pseudorapidity range abs(eta) < 1.4 with transverse energy above 145 GeV. The Z gamma to nu nu-bar gamma production cross section is measured to be 21.1 +/- 4.2 (stat.) +/- 4.3 (syst.) +/- 0.5 (lum.) fb, which agrees with the standard model prediction of 21.9 +/- 1.1 fb. The results are combined with the CMS measurement of Z gamma production in the l+ l- gamma final state (where l is an electron or a muon) to yield the most stringent limits to date on triple gauge boson couplings: abs(h3,Z) < 2.7E-3, abs(h4,Z) < 1.3E-5 for Z Z gamma and abs(h3,gamma) < 2.9E-3, abs(h4,gamma) < 1.5E-5 for Z gamma gamma couplings.
Characteristics of multi-particle production in proton-proton collisions at sqrt(s) = 7 TeV are studied as a function of the charged-particle multiplicity, Nch. The produced particles are separated ...into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity abs(eta) < 2.4 and transverse momentum pt > 0.25 GeV. Jets are reconstructed from charged-particles only and required to have pt > 5 GeV. The distributions of jet pt, average pt of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of Nch and compared to the predictions of the PYTHIA and HERWIG event generators. Predictions without multi-parton interactions fail completely to describe the Nch-dependence observed in the data. For increasing Nch, PYTHIA systematically predicts higher jet rates and harder pt spectra than seen in the data, whereas HERWIG shows the opposite trends. At the highest multiplicity, the data--model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients.
The t t-bar charge asymmetry is measured in events containing a charged lepton (electron or muon) and at least four jets, one of which is identified as originating from b-quark hadronization. The ...analyzed dataset corresponds to an integrated luminosity of 5.0 inverse femtobarns collected with the CMS detector at the LHC. An inclusive and three differential measurements of the t t-bar charge asymmetry as a function of rapidity, transverse momentum, and invariant mass of the t t-bar system are presented. The measured inclusive t t-bar charge asymmetry is A(C) = 0.004 +/- 0.010 (stat.) +/- 0.011 (syst.). This result and the three differential measurements are consistent with zero asymmetry as well as with the predictions of the standard model.
A simultaneous measurement of the top-quark, W-boson, and neutrino masses is reported for t t-bar events selected in the dilepton final state from a data sample corresponding to an integrated ...luminosity of 5.0 inverse femtobarns collected by the CMS experiment in pp collisions at sqrt(s)=7 TeV. The analysis is based on endpoint determinations in kinematic distributions. When the neutrino and W-boson masses are constrained to their world-average values, a top-quark mass value of Mt=173.9 +/- 0.9 (stat.) +1.6/-2.0 (syst.) GeV is obtained. When such constraints are not used, the three particle masses are obtained in a simultaneous fit. In this unconstrained mode the study serves as a test of mass determination methods that may be used in beyond standard model physics scenarios where several masses in a decay chain may be unknown and undetected particles lead to underconstrained kinematics.
A search for a standard-model-like Higgs boson in the H to WW and H to ZZ decay channels is reported, for Higgs boson masses in the range 145 < mH < 1000 GeV. The search is based upon proton-proton ...collision data samples corresponding to an integrated luminosity of up to 5.1 inverse femtobarns at sqrt(s) = 7 TeV and up to 5.3 inverse femtobarns at sqrt(s) = 8 TeV, recorded by the CMS experiment at the LHC. The combined upper limits at 95% confidence level on products of the cross section and branching fractions exclude a standard-model-like Higgs boson in the range 145 < mH < 710 GeV, thus extending the mass region excluded by CMS from 127-600 GeV up to 710 GeV.
The top-quark pair production cross section in 7 TeV centre-of-mass proton proton collisions is measured using data collected by the CMS detector at the LHC. The measurement uses events with one jet ...identified as a hadronically-decaying tau lepton and at least four additional energetic jets, at least one of which is identified as coming from a b quark. The analysed data sample corresponds to an integrated luminosity of 3.9 inverse femtobarns recorded by a dedicated multijet plus hadronically-decaying tau trigger. A neural network has been developed to separate the top-quark pairs from the W+jets and multijet backgrounds. The measured value of sigma(ttbar) = 152 +/- 2 (stat.) +/- 32 (syst.) +/- 3 (lum.) pb is consistent with the standard model predictions.
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