Monday, March 7, 2022

A New Bottom Quark Mass Determination

A new paper precisely estimates that the bottom quark pole mass (i.e. its mass at the energy scale of its own mass) is 4180.2 ± 7.9 MeV, assuming the global average value of the strong force coupling constant at the Z boson energy scale of 0.1182.

The uncertainty in the strong force coupling constant's value is about ± 0.0010 (dimensionless) which translates into an additional uncertainty in the bottom quark mass determination of about 1.1 MeV. So, the combined uncertainty in the estimate is about 8.0 MeV.

You could state the result without spurious accuracy as 4180(8) MeV. 

The Particle Data Group value is the same, but with a much more conservative margin of error at 4180 +30/-20 MeV. The FLAG19 value is 4198(12), which is consistent at 1.25 sigma with the new paper's result. The FLAG21 value is 4203(11) MeV, which is consistent at 1.7 sigma with the new paper's result.

This is based mostly upon precision measurements of the masses of excited bottomonium mesons, and upon calculations from perturbative quantum chromodynamics (QCD), which is the strong force part of the Standard Model, using high energy physics QCD methods, rather than the lattice QCD methods used in lower energy contexts which predominant in quark mass determination studies. The confirmation of the lattice QCD results with perturbative QCD suggests that the lattice QCD results are robust.

The two parts per thousand precision is impressive and is consistent with prior measurements.

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