Measurement of the hadronic activity in events with a Z and two jets and extraction of the cross section for the electroweak production of a Z with two jets in pp collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP10%282013%29062.The first measurement of the electroweak production cross section of a Z boson with two jets (Zjj) in pp collisions at s√=7 TeV is presented, based on a data sample recorded by the CMS experiment at the LHC with an integrated luminosity of 5 fb(−1). The cross section is measured for the ℓℓjj (ℓ = e, μ) final state in the kinematic region m(ℓℓ) > 50 GeV, m(jj) > 120 GeV, transverse momenta p(j)(T)>25 GeV and pseudorapidity |η(j)| < 4.0. The measurement, combining the muon and electron channels, yields σ = 154 ± 24 (stat.) ± 46 (exp. syst.) ± 27 (th. syst.) ± 3 (lum.) fb, in agreement with the theoretical cross section. The hadronic activity, in the rapidity interval between the jets, is also measured. These results establish an important foundation for the more general study of vector boson fusion processes, of relevance for Higgs boson searches and for measurements of electroweak gauge couplings and vector boson scattering

Inclusive b-hadron production cross section with muons in pp collisions at s√=7TeV

A measurement of the b-hadron production cross section in proton-proton collisions at s√=7TeVs=7TeV is presented. The dataset, corresponding to 85 nb−1, was recorded with the CMS experiment at the LHC using a low-threshold single-muon trigger. Events are selected by the presence of a muon with transverse momentum pμT>6GeVpTμ>6GeV with respect to the beam direction and pseudorapidity |η μ | < 2.1. The transverse momentum of the muon with respect to the closest jet discriminates events containing b hadrons from background. The inclusive b-hadron production cross section is presented as a function of muon transverse momentum and pseudorapidity. The measured total cross section in the kinematic acceptance is σ(pp → b + X → μ + X′) = 1.32 ± 0.01(stat) ± 0.30(syst) ± 0.15(lumi)μb

Measurement of the Λ(0)(b) lifetime in pp collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP07%282013%29163.A measurement of the Λ(0)(b) lifetime using the decay Λ(0)(b)→J/ψΛ in protonproton collisions at s√=7 TeV is presented. The data set, corresponding to an integrated luminosity of about 5 fb(−1), was recorded with the CMS experiment at the Large Hadron Collider using triggers that selected dimuon events in the J/ψ mass region. The Λ(0)(b) lifetime is measured to be 1.503 ± 0.052 (stat.) ± 0.031 (syst.) ps

Observation of long-range, near-side angular correlations in proton-proton collisions at the LHC

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP09%282010%29091.Results on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (η) and azimuthal angle (ϕ). Short-range correlations in Δη, which are studied in minimum bias events, are characterized using a simple “independent cluster” parametrization in order to quantify their strength (cluster size) and their extent in η (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 nb(−1) data set at 7 TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate p T of 1–3 GeV/c, 2.0 < |Δη| < 4.8 and Δϕ ≈ 0. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in pp or pp-bar collisions

Search for Dijet Resonances in 7 TeV pp Collisions at CMS

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.211801.A search for narrow resonances in the dijet mass spectrum is performed using data corresponding to an integrated luminosity of 2.9  pb(−1) collected by the CMS experiment at the Large Hadron Collider. Upper limits at the 95% confidence level are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% confidence level: string resonances, with mass less than 2.50 TeV, excited quarks, with mass less than 1.58 TeV, and axigluons, colorons, and E6 diquarks, in specific mass intervals. This extends previously published limits on these models

Measurement of the production cross section for Zγ→ν(ν-bar)γ in pp collisions at s√=7 TeV and limits on ZZγ and Zγγ triple gauge boson couplings

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP10%282013%29164.A measurement of the Zγ→ν(ν-bar)γ cross section in pp collisions at s√=7 TeV is presented, using data corresponding to an integrated luminosity of 5.0 fb(−1) 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 |η| < 1.4 with transverse energy above 145 GeV. The Zγ→ν(ν-bar)γ 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 Zγ production in the ℓ (+) ℓ (−) γ final state (where ℓ is an electron or a muon) to yield the most stringent limits to date on triple gauge boson couplings: ∣∣h(Z)(3)∣∣<2.7×10(−3) , ∣∣h(Z)(4)∣∣<1.3×10(−5) for ZZγ and ∣∣h(γ)(3)∣∣<2.9×10(−3) , ∣∣h(γ)(4)∣∣<1.5×10(−5) for Zγγ couplings

Search for new physics in events with same-sign dileptons and b jets in pp collisions at s√=8 TeV

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP03%282013%29037.A search for new physics is performed using events with isolated same-sign leptons and at least two bottom-quark jets in the final state. Results are based on a sample of proton-proton collisions collected at a center-of-mass energy of 8 TeV with the CMS detector and corresponding to an integrated luminosity of 10.5 fb(−1). No excess above the standard model background is observed. Upper limits are set on the number of events from non-standard-model sources and are used to constrain a number of new physics models. Information on acceptance and efficiencies is also provided so that the results can be used to confront an even broader class of new physics models

Measurement of the W-boson helicity in top-quark decays from tt-bar production in lepton+jets events in pp collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP10%282013%29167.The W-boson helicity fractions in top-quark decays are measured with tt-bar 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 fb(−1). The measured fractions of longitudinal, left-, and right-handed helicity are F 0 = 0.682 ± 0.030 (stat.) ± 0.033 (syst.), F L = 0.310 ± 0.022 (stat.) ± 0.022 (syst.), and F R = 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 g L , g R are also derived

Search for pair-produced dijet resonances in four-jet final states in pp collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.141802.A search for the pair production of a heavy, narrow resonance decaying into two jets has been performed using events collected in s√=7  TeV pp collisions with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 5.0  fb(−1). Events are selected with at least four jets and two dijet combinations with similar dijet mass. No resonances are found in the dijet mass spectrum. The upper limit at 95% confidence level on the product of the resonance pair production cross section, the branching fractions into dijets, and the acceptance varies from 0.22 to 0.005 pb, for resonance masses between 250 and 1200 GeV. Pair-produced colorons decaying into qq-bar are excluded for coloron masses between 250 and 740 GeV

Search for supersymmetry in final states with a single lepton, b-quark jets, and missing transverse energy in proton-proton collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.052006.A search motivated by supersymmetric models with light top squarks is presented using proton-proton collision data recorded with the CMS detector at a center-of-mass energy of s√=7  TeV during 2011, corresponding to an integrated luminosity of 4.98  fb(−1). The analysis is based on final states with a single lepton, b-quark jets, and missing transverse energy. Standard model yields are predicted from data using two different approaches. The observed event numbers are found to be compatible with these predictions. Results are interpreted in the context of the constrained minimal supersymmetric standard model and of a simplified model with four top quarks in the final state