Abstract
The top quark mass is measured using a template method in the tbar{t} rightarrow mathrm {lepton+jets} channel (lepton is e or mu ) using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton–proton centre-of-mass energy of {sqrt{s}} =8 text {TeV} and correspond to an integrated luminosity of 20.2 fb^{-1}. The tbar{t} rightarrow mathrm {lepton+jets} channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks (b). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale factor and a relative b-to-light-jet energy scale factor. The mass of the top quark is measured to be m_{mathrm {top}} =172.08 ,pm ,0.39 ,mathrm {(stat)},pm ,0.82 ,mathrm {(syst)} text {GeV}. A combination with previous ATLAS m_{mathrm {top}} measurements gives m_{mathrm {top}} = 172.69 ,pm ,0.25 ,mathrm {(stat)},pm ,0.41 ,mathrm {(syst)} text {GeV}.
Highlights
The mass of the top quark mtop is an important parameter of the Standard Model (SM)
In the analysis presented here, mtop is obtained from the combined sample of events selected in the electron+jets and muon+jets final states
The contribution of events falsely reconstructed as tt → lepton + jets events due to the presence of objects misidentified as leptons and NP leptons originating from HF decays, is estimated from data using the matrix-method [70]
Summary
The mass of the top quark mtop is an important parameter of the Standard Model (SM). Precise measurements of mtop provide crucial information for global fits of electroweak parameters [1–3] which help to assess the internal consistency of the SM and probe its extensions. The technique employed uses η- and pT-dependent efficiencies for NP/fake-leptons and promptleptons They are measured in a background-enhanced control region with low ETmiss and from events with dilepton masses around the Z boson peak [71], respectively. Given the very small contribution from Z +jets, diboson and NP/fake-lepton backgrounds, no shape uncertainty is evaluated for these background sources. The shift in mtop is quoted relative to the value measured in the central sample for the upward variation ( mutopp), the downward variation ( mdtowp) and the final shift assigned to this uncertainty component ( mtop). For most of the cases the signs of mutopp and mdtowp are different, indicating that mtop from the central sample is surrounded by the values from the two variations.
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