Another Top Quark Mass Measurement

The latest lepton decay based measurement of the top quark mass from CMS at the LHC is 173.8 -1.7+1.8 GeV.  This tends to pull up the LHC and world average measurement of this key parameter of the Standard Model.

The state of the art prior to this measurement was recapped in a December 2015 post at this blog:

The best available estimate of the mass of the top quark from the Large Hadron Collider (LHC) combining data from both the CMS and ATLAS experiments is now 172.38 +/- 0.66 GeV. The final Tevatron mass measurement for the top quark was 174.34 +/- 0.64 GeV. This brings the error weighted world average mass measurement of the top quark to about 173.35 GeV, which is consistent with both the LHC measurement and the Tevatron measurement at the 1.5 sigma level.

The previous top quark mass estimate from ATLAS (as of April of 2015) was 172.99 +/- 0.91 GeV. The latest combined LHC measurement excluding that ATLAS estimate was 173.34 +/- 0.76 GeV. Thus, the LHC mass measurement is trending down.

As noted in the Tevatron mass estimate post:

The expected value of the top mass from the formula that the sum of the square of each of the fundamental particle masses equals the square of the Higgs vaccum expectation value, given the state of the art Higgs boson mass measurement (and using a global fit value of 80.376 GeV for the W boson rather than the PDG value) is 173.73 GeV. . . . If the the sum of the square of the boson masses equals the sum of the square of the fermion masses the implied top quark mass is 174.03 GeV if pole masses of the quarks are used, and 174.05 GeV if MS masses at typical scales are used.

Thus, there are theoretical conjectures that pull the expected value of the top quark mass up from the current estimates, although those estimates are not in great tension with the current global average.

The new measurement is right on the button of value that I would expect given measurements of the Higgs boson to date, suggesting that the sum of the squares of the fundamental particle masses do indeed equal the sum of the square of the Higgs vacuum expectation value.

It is also consistent with the refined possibility that the sum of the square of the fundamental fermion masses equals the sum of the square of the fundamental boson masses.

This leaves very little room for new beyond the Standard Model particles (at least if they interact with the 125 GeV Higgs boson's field).