Thursday, September 1, 2022

A New Top Quark Mass Measurement From ATLAS

The best fit value of the latest top quark mass measurement at ATLAS of 174.41 GeV is quite a bit higher (1.72 GeV higher to be exact) than the Particle Data Group world average of 172.69 ± 0.30 GeV. 

But, the uncertainty of the new measurement of a combined 0.81 GeV is quite large, so the two values are actually consistent at the two sigma level.  And due to its greater uncertainty, the new measurement won't change the inverse uncertainty weighted world average much either.

A measurement of the top-quark mass (mt) in the tt¯→ lepton+jets channel is presented, with an experimental technique which exploits semileptonic decays of b-hadrons produced in the top-quark decay chain. The distribution of the invariant mass mℓμ of the lepton, ℓ (with ℓ=e,μ), from the W-boson decay and the muon, μ, originating from the b-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract mt. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb−1 of s√=13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is mt=174.41±0.39 (stat.)±0.66 (syst.)±0.25 (recoil) GeV, where the third uncertainty arises from changing the PYTHIA8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup.
ATLAS Collaboration, "Measurement of the top-quark mass using a leptonic invariant mass in pp collisions at s√=13 TeV with the ATLAS detector" arXiv:2209.00583 (September 1, 2022).

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