Measurement of thett¯production cross section inppcollisions at 7 TeV inlepton+

Abstract

A new measurement of the inclusive production cross section for pp ! t " t is performed at a center-ofmass energy of 7 TeV using data collected by the CMS experiment at the LHC. The analysis uses a data sample corresponding to an integrated luminosity of 36 pb À1 , and is based on the final state with one isolated, high transverse momentum muon or electron, missing transverse energy, and hadronic jets. The t " t content of the selected events is enhanced by requiring the presence of at least one jet consistent with b-quark hadronization. The measured cross section is 150 AE 9ðstatÞ AE 17ðsystÞ AE 6ðlumiÞ pb and is in agreement with higher-order QCD calculations. The combination of this measurement with a previous CMS result based on dileptons gives 154 AE 17ðstat þ systÞ AE 6ðlumiÞ pb.

Identification of b-quark jets in the CMS experiment

“…The uncertainty was determined in the same way as in top-quark pair production. The normalizations of the W+b jets and W+c jets components were determined in a measurement of the top pair production cross section in the lepton+jet channel [22], where a simultaneous fit of the tt cross section and the normalization of the main backgrounds was performed.…”

“…The uncertainty was determined in the same way as in top-quark pair production. The normalizations of the W+b jets and W+c jets components were determined in a measurement of the top pair production cross section in the lepton+jet channel [22], where a simultaneous fit of the tt cross section and the normalization of the main backgrounds was performed.The Drell-Yan production cross section at NNLO was calculated using FEWZ as σ Z/γ * → (m > 20 GeV) = 5.00 ± 0.27 nb, where m is the invariant mass of the two leptons and the scales were set using the Z boson mass m Z = 91.1876 GeV/c 2 [23].All generated events were passed through the full simulation of the CMS detector based on GEANT4 [24]. The samples were generated with a different pileup distribution than that observed in the data.…”

“…The uncertainties include the uncertainties on the luminosity measurement and the cross sections. For all MC predictions, events are reweighted to take into account differences in trigger and lepton selection efficiencies between data and simulation [22,41]. The lepton selection efficiency scale factors are estimated from data using Z events.…”

Search for heavy bottom-like quarks in 4.9 fb−1 of pp collisions at $ \sqrt {s} = 7 $ TeV

“…The uncertainties in the background normalization are estimated to be 0.74 and 0.12 events for dilepton and trilepton channels, respectively, and the uncertainties for each of the individual processes are included as follows: ±11% for tt [41], ±3% (±4%) for W (Z) [42], ±30% for single top processes, ±26% for WW, ±30% for WZ, ±21% for ZZ, ±30% for ttW, ±30% for ttZ, ±49% for W ± W ± +jets, and ±100% for multijet. The uncertainties in the normalization of diboson, ttW, ttZ, and W ± W ± +jets processes are taken from a comparison of next-to-leading-order and leading-order predictions.…”

“…The yield in the signal region, which is only 0.78 ± 0.21 events, is estimated using simulated samples. Contributions from pp → tt and W/Z processes are normalized to the cross sections measured by CMS [41,42]. The single-top contributions are normalized to the next-to-next-to-leading-logarithm cross sections [43,44].…”