Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at 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.Funded by SCOAP

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

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

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 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

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 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

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 heavy quarks decaying into a top quark and a W or Z boson using 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%2FJHEP01%282013%29154.Results are presented from a search for the pair-production of heavy quarks, QQ-bar , that decay exclusively into a top quark and a W or Z boson. The search is performed using a sample of proton-proton collisions at s√=7 TeV corresponding to an integrated luminosity of 5.0 fb(−1), collected by the Compact Muon Solenoid experiment. The signal region is defined using a sample of events containing one electron or muon, missing transverse momentum, and at least four jets with large transverse momenta, where one jet is likely to originate from the decay of a bottom quark. No significant excess of events is observed with respect to the standard model expectations. Assuming a strong pair-production mechanism, quark masses below 675 (625) GeV decaying into tW (tZ) are excluded at the 95 % confidence level

Measurement of neutral strange particle production in the underlying event 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.88.052001.Measurements are presented of the production of primary K(0)(S) and Λ particles in proton-proton collisions at s√=7  TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of K(0)(S) and Λ particles measured at pseudorapidities |η|<2 rise with increasing charged-particle jet p(T) in the range 1–10  GeV/c and saturate in the region 10–50  GeV/c. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the pythia Monte Carlo event generator. The pythia simulations underestimate the data by 15%–30% for K(0)(S) mesons and by about 50% for Λ baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet p(T) and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage