A New Top Quark Mass Measurement

The top quark is the most massive fundamental particle in the Standard Model. A new work makes a precision LHC measurement by using clever methods to reduce jet scale associated uncertainty. The bottom line value from the new work is:

m(t) = 172.5 ± 1.2 GeV

This compared to the PDG global average of:

m(t) = 172.4 ± 0.7 GeV

Prior measurements are summarized as follows:

More background is recapped at a previous post at this blog about the top quark mass. 

Theoretical expectations

(1) global electroweak fits favor a top quark mass of:

m(t) = 173.52 ± 0.88 GeV

This is consistent with the Particle Data Group value at a 1 sigma level (given the uncertainties in both the PDG value and the prediction).

But fairly slight adjustments down of the W boson mass from the current estimate of 80.385 ± 0.015 GeV down by one or two standard deviations from this value would favor a somewhat lower global electroweak fit expectation for the top quark mass.

(2) an extended Koide's rule favors a top quark mass of:

m(t) = 173.263 947 ± 0.000 006 GeV

This is consistent with the Particle Data Group value at a 1.2 sigma level.

(3) the expectation of that sum of the square of the fundamental particle masses in the Standard Model is equal to the square of the Higgs vacuum expectation value (using PDG values) favors a top quark mass of about:

m(t) = 173.71 GeV

This is consistent with the Particle Data Group value at a 1.9 sigma level.

The Higgs vacuum expectation value is 246.21965 ± 0.00060 GeV. The Higgs boson mass is currently 125.10 ± 0.14 GeV according to the Particle Data Group 

Increases in the measured value of the Higgs boson mass (currently ) can push this to a somewhat smaller value, although not on a one to one basis, so any adjustment in the Higgs boson mass that is plausible would not shift this down a great deal.

The best fit in terms of deviation from the Particle Data Group values (using an electroweak fit value for the W boson mass) to fit the top quark mass and Higgs boson mass to these relationships at a 1.1 sigma level would be a top quark mass of 173.15 GeV and a Higg boson mass of 125.28 GeV.

(4) the expectation of that sum of the square of the fundamental fermion masses in the Standard Model is equal to half of the square of the Higgs vacuum expectation value favors a top quark mass of:

m(t) = 174.04 GeV.

This is 2.3 sigma higher than the Particle Data Group global average and hence in tension with it, although not absolutely ruled out.

This assumption also favors a Higgs boson mass of 124.65 GeV, which is about 3.3 sigma below the measured value, also in strong tension with the measured value.

So, this fourth theoretical expectation that the sum of the square of fundamental fermion masses equals half of the Higgs vacuum expectation value squared and that the sum of the square of the fundamental boson masses equals half of the Higgs vacuum expectation value squared, is probably not true. We live in a "boson heavy" universe by this measure.

UPDATE: See also this preprint.

[Submitted on 8 Oct 2020]

Simultaneous extraction of αs and mt from LHC tt¯ differential distributions

Amanda M. Cooper-Sarkar, Michal Czakon, Matthew A. Lim, Alexander Mitov, Andrew S. Papanastasiou

We present a joint extraction of the strong coupling αs and the top-quark pole mass mt from measurements of top-quark pair production performed by the ATLAS and CMS experiments at the 8 TeV LHC. For the first time, differential NNLO theory predictions for different values of the top-quark mass are utilised for four kinematic distributions: the average transverse momentum of the top-quark, its average rapidity and the pair invariant mass and rapidity. The use of fastNLO tables for these distributions allows rapid evaluation of the differential theory predictions for different PDF sets. We consider the single differential distributions from the experiments both separately and in combination in order to obtain the best fit to theory. Our final values are αs=0.1159+0.0013−0.0014 and mt=173.8+0.8−0.8 GeV which are compatible with previous extractions using top-quark measurements. In the case of mt, our value is also compatible with the world average value collated by the Particle Data Group.

Comments:	35 pages. Supplementary results available at this http URL
Subjects:	High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Report number:	CAVENDISH-HEP-20/12, TTK-20-31, P3H-20-051
Cite as:	arXiv:2010.04171 [hep-ph]
	(or arXiv:2010.04171v1 [hep-ph] for this version)