Friday, November 4, 2022

A New Top Quark Mass Estimate From CMS

The CMS experiment at the Large Hadron Collider (LHC) has produced a new estimate of the top quark mass of 172.76 ± 0.81 GeV from hadron decays of top quark pairs (based upon a cross-section analysis) with a single measurement precision that rivals the global average of all prior experiments done with the same methods.

The Particle Data Group global average is currently 172.69 ± 0.3 GeV from direct measurements and 172.5 ± 0.7 GeV from indirect cross-section measurements, so the new result is consistent with past estimates. 

The new result from CMS probably won't adjust the global average much because it is close to the existing global average. But, it may bring the indirect cross-section measurement average closer into line with the direct measurement average and may reduce the uncertainty in the global average cross-section value. The increasing similarity of the values in both methods of measuring the top quark mass also increases the confidence we can have in the correctness of both kinds of measurements.

Previously, estimates of the top quark mass from hadronic decays have had very large uncertainties of more than 2.5 GeV. This study has tamed these uncertainties with new methods that better calibrate the mass of jets from the decays of these two very massive fundamental particles, which were previously a leading source of experimental uncertainties in these measurements.

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