Abstract
The $t\bar{t}$ production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton--proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb$^{-1}$. Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80 GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities.
Highlights
The ttproduction cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel
The data are compared to predictions from POWHEG+PYTHIA, POWHEG(hdamp)+PYTHIA with varied amount of hard radiation, ALPGEN+HERWIG and ALPGEN+PYTHIA with αS variations, Monte Carlo (MC)@next-to-leading order (NLO) +HERWIG and the POWHEG+PYTHIA MC models
The fiducial ttproduction cross-section in pp collisions at 7 TeV is presented as a function of the jet multiplicity for up to eight jets with jet pT thresholds of 25, 40, 60, and 80 GeV using 4.6 fb−1 of data
Summary
The ttproduction cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel. The production of additional jets in ttevents is sensitive to higher-order perturbative QCD effects. Ttproduction with additional jets is a dominant background in certain Higgs boson production processes and decay modes and to many searches for new physics phenomena [3, 4]. Tests similar to those presented in this paper have been performed at lower energies, using measurements of jets associated with colour-singlet vector-boson production at the LHC [5, 6] and at the Tevatron [7,8,9,10]. Selected events are classified by the decay of one or both of the W bosons into leptons, as either single-lepton or dilepton channel, respectively
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