Abstract
The first measurement of the top quark pair production cross section in the fully hadronic channel at a center-of-mass energy of $\sqrt s = 7$ TeV is presented. The measurement has been performed using an integrated luminosity of 1.09 fb$^{-1}$, collected with the CMS detector. The reconstruction of the $t\bar t$ candidates is performed after a cut-based event selection using a kinematic fit. A data-driven technique is used to estimate the dominant background from QCD multijet production. The cross section is determined from a fit to the top quark mass. The cross section measurement yields $\sigma(t\bar t)=136 \pm 20 (stat.) \pm 40 (sys.) \pm 8 (lumi.)$ pb. This result is consistent with an independent measurement in the same channel, with the measurements in other decay channels and with the Standard Model predictions.
Highlights
Measurements of the top quark pair production cross section in proton-proton collisions at the LHC provide important tests of our understanding of the top quark production mechanism and can be used in new physics searches
The reconstruction of the ttcandidates is performed after a cut-based event selection using a kinematic fit
The number of signal events after the final selection is determined via an unbinned maximum likelihood fit to the reconstructed top quark mass distribution, obtained from the kinematic fit
Summary
Measurements of the top quark pair production cross section in proton-proton collisions at the LHC provide important tests of our understanding of the top quark production mechanism and can be used in new physics searches. The first cross section measurement in the fully hadronic decay channel with the CMS detector is presented [5]. The fully hadronic decay channel has the largest signal yield compared to the dilepton and lepton+jets channels. With only jets in the final state, this channel is dominated by the nearly identical QCD multijet background. This measurement demonstrates the good understanding of the CMS detector and is, an important milestone. This measurement was combined with the more recent measurements in the other channels, providing the most precise CMS measurement obtained to date
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