A New Top Quark Mass Measurement

The latest top quark mass measurement at the Large Hadron Collider (LHC) is on the low side relative to previous measurements and the global average (which is 172.69 ± 0.30 from direct measurements), and is fairly precise despite using a fairly complex set of decay products to measure it. 

The new measurement is 1.93 sigma from the global average, so the new measurement is just barely consistent with the global average. In contrast, many other recent LHC measurements of the top quark mass have been high (almost two sigma high in at least one case) relative to the global average.

The mass of the top quark is measured in 36.3 fb−1 of LHC proton-proton collision data collected with the CMS detector at s√ = 13 TeV. The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to five observables to extract the top quark mass. The top quark mass is measured to be 171.77 ± 0.37 GeV. This approach significantly improves the precision over previous measurements.

CMS Collaboration, "Measurement of the top quark mass using a profile likelihood approach with the lepton+jets final states in proton-proton collisions at s√ = 13 TeV" arXiv:2302.01967 (February 3, 2023).