Search for physics beyond the standard model using multilepton signatures in pp collisions at √s=7 TeV

A search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb^(−1) of integrated luminosity in pp collisions at √s=7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space

Measurement of the Inclusive Jet Cross Section in pp Collisions at √s = 7 TeV

The inclusive jet cross section is measured in pp collisions with a center-of-mass energy of 7 TeV at the Large Hadron Collider using the CMS experiment. The data sample corresponds to an integrated luminosity of 34  pb^(-1). The measurement is made for jet transverse momenta in the range 18–1100 GeV and for absolute values of rapidity less than 3. The measured cross section extends to the highest values of jet p_T ever observed and, within the experimental and theoretical uncertainties, is generally in agreement with next-to-leading-order perturbative QCD prediction

Measurement of the inclusive Z cross section via decays to tau pairs in pp collisions at √s = 7 TeV

The first measurement of inclusive Z → τ^+ τ^− production in pp collisions at the LHC is presented, in the final states μ + hadrons, e + hadrons, e + μ, and μ + μ. The data sample corresponds to an integrated luminosity of 36 pb^(−1) collected with the CMS detector. The measured cross section is σ (pp → ZX) × B (Z → τ^+ τ^−) = 1.00 ± 0.05(stat.) ± 0.08(syst.) ± 0.04(lumi.)nb, which is in good agreement with the next-to-next-to-leading order QCD prediction and improves on previous measurements in the Z → e^+e^− and μ^+ μ^− channels. The reconstruction efficiency for hadronic τ decays is determined with a precision of 7%

Measurement of the underlying event activity at the LHC with √s = 7 TeV and comparison with √s = 0.9 TeV

A measurement of the underlying activity in events with a jet of transverse momentum in the several GeV region is performed in proton-proton collisions at √s = 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |η| 0.5 GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A signicant growth of the average multiplicity and scalar-p_T sum of the particles in the transverse region is observed with increasing p_T of the leading trackjet, followed by a much slower rise above a few GeV/c. For track-jet p_T larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centre-of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in pythia are compared to the data

Measurement of the B^0 Production Cross Section in pp Collisions at √s=7 TeV

Measurements of the differential production cross sections dσ/dp_T^B and dσ/dy^B for B^0 mesons produced in pp collisions at √s=7  TeV are presented. The data set used was collected by the CMS experiment at the LHC and corresponds to an integrated luminosity of 40  pb^(-1). The production cross section is measured from B^0 meson decays reconstructed in the exclusive final state J/ψK_S^0, with the subsequent decays J/ψ→μ^+μ^- and K_S^0→π^+π^-. The total cross section for p_T^B>5  GeV and |y^B|<2.2 is measured to be 33.2±2.5±3.5  μb, where the first uncertainty is statistical and the second is systematic

Forward energy flow, central charged-particle multiplicities, and pseudorapidity gaps in W and Z boson events from pp collisions at √s =7 TeV

A study of forward energy flow and central charged-particle multiplicity in events with W and Z bosons decaying into leptons is presented. The analysis uses a sample of 7 TeV pp collisions, corresponding to an integrated luminosity of 36 pb^(−1), recorded by the CMS experiment at the LHC. The observed forward energy depositions, their correlations, and the central charged-particle multiplicities are not well described by the available non-diffractive soft-hadron production models. A study of about 300 events with no significant energy deposited in one of the forward calorimeters, corresponding to a pseudorapidity gap of at least 1.9 units, is also presented. An indication for a diffractive component in these events comes from the observation that the majority of the charged leptons from the W(Z) decays are found in the hemisphere opposite to the gap. When fitting the signed lepton pseudorapidity distribution of these events with predicted distributions from an admixture of diffractive (pompyt) and non-diffractive (pythia) Monte Carlo simulations, the diffractive component is determined to be (50.0 ± 9.3 (stat.) ± 5.2 (syst.))%