Search for supersymmetry in electroweak production with photons and large missing transverse energy in pp collisions at sqrt(s) = 8 TeV

Results are reported from a search for supersymmetry with gauge-mediated supersymmetry breaking in electroweak production. Final states with photons and large missing transverse energy ( View the MathML sourceETmiss) were examined. The data sample was collected in pp collisions at View the MathML sources=8TeV with the CMS detector at the LHC and corresponds to 7.4View the MathML sourcefb−1. The analysis focuses on scenarios in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape undetected. The data were obtained using a specially designed trigger with dedicated low thresholds, providing good sensitivity to signatures with photons, View the MathML sourceETmiss, and low hadronic energy. No excess of events over the standard model expectation is observed. The results are interpreted using the model of general gauge mediation. With the wino mass fixed at 10View the MathML sourceGeV above that of the bino, wino masses below 710View the MathML sourceGeV are excluded at 95% confidence level. Constraints are also set in the context of two simplified models, for which the analysis sets the lowest cross section limits on the electroweak production of supersymmetric particles

Measurements of t t-bar spin correlations and top quark polarization using dilepton final states in pp collisions at sqrt(s) = 8 TeV

Measurements of the top quark-antiquark (tt¯) spin correlations and the top quark polarization are presented for tt¯ pairs produced in pp collisions at s√=8  TeV. The data correspond to an integrated luminosity of 19.5  fb−1 collected with the CMS detector at the LHC. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The spin correlations and polarization are measured from the angular distributions of the two selected leptons, both inclusively and differentially, with respect to the invariant mass, rapidity, and transverse momentum of the tt¯ system. The measurements are unfolded to the parton level and found to be in agreement with predictions of the standard model. A search for new physics in the form of anomalous top quark chromo moments is performed. No evidence of new physics is observed, and exclusion limits on the real part of the chromo-magnetic dipole moment and the imaginary part of the chromo-electric dipole moment are evaluated

Observation of top quark pairs produced in association with a vector boson in pp collisions at sqrt(s) = 8 TeV

Measurements of the cross sections for top quark pairs produced in association with a W or Z boson are presented, using 8TeV pp collision data corresponding to an integrated luminosity of 19.5 fb1, collected by the CMS experiment at the LHC. Final states are selected in which the associated W boson decays to a charged lepton and a neutrino or the Z boson decays to two charged leptons. Signal events are identied by matching reconstructed objects in the detector to specic nal state particles from ttW or ttZ decays. The ttW cross section is measured to be 382+117 102 fb with a signicance of 4.8 standard deviations from the background-only hypothesis. The ttZ cross section is measured to be 242+65 55 fb with a signicance of 6.4 standard deviations from the background-only hypothesis. These measurements are used to set bounds on ve anomalous dimension-six operators that would aect the ttW and ttZ cross sections

Differential cross section measurements for the production of a W boson in association with jets in proton-proton collisions at sqrt(s) = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pTpT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HTHT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb−1. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pTpT distributions of the leading jets at high pTpT values, the distributions of the HTHT at high-HTHT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values

Pseudorapidity dependence of long-range two-particle correlations in pPb collisions at sqrt(s_NN) = 5.02 TeV

Two-particle correlations in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV are studied as a function of the pseudorapidity separation (\u394\u3b7) of the particle pair at small relative azimuthal angle (|\u394\u3d5|<\u3c0/3). The correlations are decomposed into a jet component that dominates the short-range correlations (|\u394\u3b7|<1), and a component that persists at large \u394\u3b7 and may originate from collective behavior of the produced system. The events are classified in terms of the multiplicity of the produced particles. Finite azimuthal anisotropies are observed in high-multiplicity events. The second and third Fourier components of the particle-pair azimuthal correlations, V2 and V3, are extracted after subtraction of the jet component. The single-particle anisotropy parameters v2 and v3 are normalized by their laboratory frame midrapidity value and are studied as a function of \u3b7c.m.. The normalized v2 distribution is found to be asymmetric about \u3b7c.m.=0, with smaller values observed at forward pseudorapidity, corresponding to the direction of the proton beam, while no significant pseudorapidity dependence is observed for the normalized v3 distribution within the statistical uncertainties

Measurement of the W+W- cross section in pp collisions at sqrt(s) = 8 TeV and limits on anomalous gauge couplings

A measurement of the W boson pair production cross section in proton-proton collisions at $\sqrt{s} = 8$ TeV is presented. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 19.4$\,\text {fb}^\text {-1}$. The ${{\mathrm{W} }^{+} }\mathrm{W}^{-}$ candidates are selected from events with two charged leptons, electrons or muons, and large missing transverse energy. The measured ${{\mathrm{W} }^{+} }\mathrm{W}^{-}$ cross section is $60.1\pm 0.9\,\text {(stat)} \pm 3.2\,\text {(exp)} \pm 3.1\,\text {(theo)} \pm 1.6\,\text {(lumi)} \text {\,pb} = 60.1\pm 4.8\text {\,pb}$, consistent with the standard model prediction. The ${{\mathrm{W} }^{+} }\mathrm{W}^{-}$ 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 $-5.7< c_{\mathrm {WWW}}/\Lambda ^2 < 5.9\,\mathrm{TeV}^{-2}$, $-11.4< c_{\mathrm {W}}/\Lambda ^2 < 5.4\,\mathrm{TeV}^{-2}$, $-29.2< c_{\mathrm {B}}/\Lambda ^2 < 23.9\,\mathrm{TeV}^{-2}$, in the HISZ basis

Measurement of the Z boson differential cross section in transverse momentum and rapidity in proton-proton collisions at 8 TeV

We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy View the MathML sources=8 TeV, corresponding to an integrated luminosity of 19.7 fb 121. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the fewz program. The results are also compared to the commonly used leading-order MadGraph and next-to-leading-order powheg generators

Search for standard model production of four top quarks in the lepton + jets channel in pp collisions at sqrt(s) = 8 TeV

A search is presented for standard model (SM) production of four top quarks (tt\uaftt\uaf) in pp collisions in the lepton + jets channel. The data correspond to an integrated luminosity of 19.6 fb 121 recorded at a centre-of-mass energy of 8 TeV with the CMS detector at the CERN LHC. The expected cross section for SM tt\uaftt\uaf production is \u3c3SMtt\uaftt\uaf 481fb. A combination of kinematic reconstruction and multivariate techniques is used to distinguish between the small signal and large background. The data are consistent with expectations of the SM, and an upper limit of 32 fb is set at a 95% confidence level on the cross section for producing four top quarks in the SM, where a limit of 32 \ub1 17 fb is expected

Distributions of topological observables in inclusive three- and four-jet events in pp collisions at sqrt(s) = 7 TeV

This paper presents distributions of topological observables in inclusive three- and four-jet events produced in pp collisions at a centre-of-mass energy of 7 with a data sample collected by the CMS experiment corresponding to a luminosity of 5.1. The distributions are corrected for detector effects, and compared with several event generators based on two- and multi-parton matrix elements at leading order. Among the considered calculations, MadGraph interfaced with Pythia6 displays the overall best agreement with data

Search for the associated production of the Higgs boson with a top-quark pair

A search for the standard model Higgs boson produced in association with a top-quark pair (tt\uafH) is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb 121 and 19.7 fb 121 collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H \u2192 hadrons, H \u2192 photons, and H \u2192 leptons. The results are characterized by an observed tt\uafH signal strength relative to the standard model cross section, \u3bc=\u3c3/\u3c3 SM,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is \u3bc = 2.8 \ub1 1.0 for a Higgs boson mass of 125.6 GeV