Measurement of the tt̄ production cross section in the τ+jets channel in pp collisions at √s = 7 TeV

The top-quark pair production cross section in 7 TeV center-of-mass energy 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 τ lepton and at least four additional energetic jets, at least one of which is identified as coming from a b quark. The analyzed data sample corresponds to an integrated luminosity of 3.9 fb-1 recorded by a dedicated multijet plus hadronically decaying τ trigger. A neural network has been developed to separate the top-quark pairs from the W+jets and multijet backgrounds. The measured value of σtt̄= 152 ± 12,(stat.) ± 32,(syst.) ±,(lum.) pb is consistent with the standard model predictions. © 2013 CERN for the benefit of the CMS collaboration.

Search for supersymmetry in events with opposite-sign dileptons and missing transverse energy using an artificial neural network

In this paper, a search for supersymmetry (SUSY) is presented in events with two opposite-sign isolated leptons in the final state, accompanied by hadronic jets and missing transverse energy. An artificial neural network is employed to discriminate possible SUSY signals from a standard model background. The analysis uses a data sample collected with the CMS detector during the 2011 LHC run, corresponding to an integrated luminosity of 4.98 fb-1 of proton-proton collisions at the center-of-mass energy of 7 TeV. Compared to other CMS analyses, this one uses relaxed criteria on missing transverse energy (EÌ̧T>40 GeV) and total hadronic transverse energy (HT>120 GeV), thus probing different regions of parameter space. Agreement is found between standard model expectation and observations, yielding limits in the context of the constrained minimal supersymmetric standard model and on a set of simplified models. © 2013 CERN.

Search for Z′ resonances decaying to tt̄ in dilepton+jets final states in pp collisions at √s=7 TeV

A search for resonances decaying to top quark-antiquark pairs is performed using a dilepton+jets data sample recorded by the CMS experiment at the LHC in pp collisions at √s=7 TeV corresponding to an integrated luminosity of 5.0 fb-1. No significant deviations from the standard model background are observed. Upper limits are presented for the production cross section times branching fraction of top quark-antiquark resonances for masses from 750 to 3000 GeV. In particular, the existence of a leptophobic topcolor particle Z′ is excluded at the 95% confidence level for resonance masses MZ ′<1.3 TeV for ΓZ′=0.012MZ ′, and M<1.9 TeV for ΓZ′=0.10MZ ′. © 2013 CERN.

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

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 qq̄ are excluded for coloron masses between 250 and 740 GeV. © 2013 CERN. citation, and DOI.

Search for new physics in final states with a lepton and missing transverse energy in pp collisions at the LHC

This Letter describes the search for an enhanced production rate of events with a charged lepton and a neutrino in high-energy pp collisions at the LHC. The analysis uses data collected with the CMS detector, with an integrated luminosity of 5.0 fb-1 at √s=7 TeV, and a further 3.7 fb -1 at √s=8 TeV. No evidence is found for an excess. The results are interpreted in terms of limits on a heavy charged gauge boson (W ′) in the sequential standard model, a split universal extra dimension model, and contact interactions in the helicity-nonconserving model. For the last, values of the binding energy below 10.5 (8.8) TeV in the electron (muon) channel are excluded at a 95% confidence level. Interpreting the ℓν final state in terms of a heavy W′ with standard model couplings, masses below 2.90 TeV are excluded. © 2013 CERN.