Abstract
The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for $t\bar{t}$ events in the lepton+jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum for values above 300 GeV. The hadronically decaying top quark is reconstructed as an anti-$k_t$ jet with radius parameter $R=1.0$ and identified with jet substructure techniques. The observed yield is corrected for detector effects to obtain a cross-section at particle level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of a majority of next-to-leading-order and leading-order matrix-element Monte Carlo generators are found to agree with the measured cross-sections.
Highlights
The large number of top–antitop quark pairs produced at the LHC provide a unique opportunity to improve our understanding of tt production and test the Standard Model (SM) at the TeV scale
Charged-particle trajectories are reconstructed by the inner detector, which covers pseudorapidity jηj < 2.5 and is composed of a silicon pixel detector, a silicon microstrip detector, and a transition radiation tracker (TRT)
The uncertainties due to QCD initial- and final-state radiation (ISR and FSR) modeling are estimated with samples generated with AcerMC v3.8[43], interfaced to Pythia for which the parton shower parameters are varied according to a measurement of the additional jet activity in tt events [44]
Summary
The large number of top–antitop quark (tt) pairs produced at the LHC provide a unique opportunity to improve our understanding of tt production and test the Standard Model (SM) at the TeV scale. The selection and reconstruction are based on an algorithm developed [17] and used in tt resonance searches [18,19,20,21] that increases the tt selection efficiency at high top quark pT and extends the kinematic reach into the TeV range This analysis utilizes the lepton þ jets channel where one W boson decays hadronically and the other leptonically to an electron or a muon, assuming each top quark decays to a W boson and a b-quark. The object definition, event selection, and background determination used in this analysis follow closely the ones used in the search for tt resonances [20] More details of these aspects of the measurement can be found in the corresponding reference
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