A New Higgs Boson Mass Measurement From ATLAS And More

The Higgs boson mass is a fundamental parameter of the Standard Model of Particle Physics that is the principle experimentally measured parameter that impacts its properties. 

The latest ATLAS measurement of its mass through one of two main decay channels used to measure it, is closely in line, after Run 2, with the value that it had as measured by ATLAS after Run 1. The main difference is that the uncertainty in the result, which is mostly a product of the sample size of the data used to make it, is reduced by about 28%.

This heightens the existing 1.5 sigma discrepancy between the combined ATLAS result and the combined CMS result which at the end of Run 1 was 0.41 GeV higher than the ATLAS measurement and claimed a significantly lower uncertainty. But, we don't yet have a Run 2 measurement from CMS.

The Particle Data Group error weighted global average value of the Higgs boson mass (which does not include this new result) is 125.25 ± 0.17 GeV.

The mass of the Higgs boson is measured in the H→ZZ∗→4ℓ decay channel. The analysis uses proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. 

The measured value of the Higgs boson mass is 124.99±0.18(stat.)±0.04(syst.) GeV and is based on improved momentum-scale calibration for muons relative to previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. 

This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass measurement of 124.94±0.17(stat.)±0.03(syst.) GeV.

ATLAS Collaboration, "Measurement of the Higgs boson mass in the H→ZZ∗→4ℓ decay channel using 139 fb−1 of s√=13 TeV pp collisions recorded by the ATLAS detector at the LHC" arXiv:2207.00320 (July 1, 2022).

The introduction to the paper notes that:

The mass of the Higgs boson was measured to be 125.09 ± 0.24 GeV in a combined analysis performed by the ATLAS and CMS collaborations using approximately 25 fb−1 of √ 𝑠 = 7 and 8 TeV 𝑝 𝑝 collision data recorded in 2011 and 2012, respectively, commonly referred to as Run 1. The individual measurements used the 𝐻 → 𝑍 𝑍∗ → 4ℓ (where ℓ = 𝑒 or 𝜇) and 𝐻 → 𝛾𝛾 decay modes because of their excellent mass resolution.

The ATLAS Collaboration reported a measurement of 𝑚𝐻 using the 𝐻 → 𝑍 𝑍∗ → 4ℓ and 𝐻 → 𝛾𝛾 channels with 36.1 fb−1 of √ 𝑠 = 13 TeV 𝑝 𝑝 collision data recorded in 2015 and 2016. This was combined with the Run 1 ATLAS measurement to obtain a value of 𝑚𝐻 = 124.97 ± 0.24 GeV. The CMS Collaboration measured 𝑚𝐻 using the 𝐻 → 𝑍 𝑍∗ → 4ℓ and 𝐻 → 𝛾𝛾 channels with 35.9 fb−1 of √ 𝑠 = 13 TeV 𝑝 𝑝 collision data recorded in 2015 and 2016. This was combined with the Run 1 CMS measurement to obtain a value of 𝑚𝐻 = 125.38 ± 0.14 GeV.

This paper reports a new measurement of 𝑚𝐻 in the 𝐻 → 𝑍 𝑍∗ → 4ℓ channel using a 139 fb−1 dataset of 13 TeV 𝑝 𝑝 collisions produced by the LHC and recorded by the ATLAS detector between 2015 and 2018, commonly referred to as Run 2.

New Strange Quark Related Physical Constant Values

This week also brings a new determination of the strange quark mass and of a related CKM matrix element, both based upon tau lepton decays. But, these determinations are less notable as the uncertainties in them are quite large.

We determine the strange quark mass (ms) and quark mixing element |Vus|, and their joint determination from the Cabibbo suppressed hadronic τ decays in various perturbative schemes. Compared to the previous analysis based on the optimal renormalization or the renormalization group summed perturbation theory (RGSPT) scheme, we have improved this analysis by replacing the theoretical longitudinal contributions with phenomenological parametrization, and the RGSPT coefficients are used for the dimension-4 Adler functions. The improved analysis results in the extraction of ms(2GeV)=97±15MeV and |Vus|=0.2190±0.0016 from the RGSPT scheme.

B. Ananthanarayan, Diganta Das, M. S. A. Alam Khan, "Renormalization group improved ms and |Vus| determination from hadronic τ decays" arXiv:2207.00754 (July 2, 2022).

The Particle Data Group error weighted global average value of the strange quark mass (which does not include this new result) is 93.4 + 8.6 -3.4 MeV which is about 0.2 sigma from the new result from tau lepton decays.

The global fit value that the Particle Data Group (which does not include this new result) provides for CKM matrix element |Vus| is 0.22500 ± 0.00067, which is in a 3.5 sigma tension with the new result from tau lepton decays.

The global fit value is heavily influenced by the more precisely measured kaon decay data, but the comparable Particle Data Group value obtained from tau lepton decays is |Vus| is 0.2221 ± 0.0013, which is 1.5 sigma higher than this new result.

The new results aren't perfectly comparable to the PDG results, however, because they involved different renormalization schemes.

Vus|= 0.2221±0.0013Vus|= 0.2243±0.000