In the eleven years since its discovery, studies of the Higgs boson have become a central avenue for shedding light on the fundamental structure of the Universe. Precise measurements of Higgs-boson properties are among the most powerful tools physicists have to put pressure on the Standard Model — and now, it’s the turn of the Higgs-boson mass.
Candidate Higgs boson decays into two photons in the ATLAS experiment. Image credit: CERN.
The mass of the Higgs boson is not predicted by the Standard Model, and must be determined experimentally.
A precise assessment of its value is of paramount importance in particle physics.
The interaction (or coupling) strength of the Higgs boson with Standard-Model particles depends on the Higgs-boson mass, and can only be calculated once the value of the mass is known.
More importantly, the value of the Higgs-boson mass is intimately related to the properties of the Higgs potential — which determines the stability of the electroweak vacuum, and potentially the fate and evolution of our Universe.
The ATLAS and CMS collaborations at CENR’s Large Hadron Collider (LHC) have been making ever more precise measurements of the Higgs boson’s mass since the particle’s discovery.
The new ATLAS measurement combines two results: a new Higgs boson mass measurement based on an analysis of the particle’s decay into two high-energy photons (diphoton channel) and an earlier mass measurement based on a study of its decay into four leptons (four-lepton channel).
The new measurement in the diphoton channel, which combines analyses of the full ATLAS data sets from Runs 1 and 2 of the LHC, resulted in a mass of 125.22 billion electronvolts (GeV) with an uncertainty of only 0.14 GeV.
With a precision of 0.11%, this diphoton-channel result is the most precise measurement to date of the Higgs boson’s mass from a single decay channel.
“The advanced and rigorous calibration techniques used in this analysis were critical for pushing the precision to such an unprecedented level,” said Dr. Stefano Manzoni, convener of the ATLAS electron-photon calibration subgroup.
“Their development took several years and required a deep understanding of the ATLAS detector. They will also greatly benefit future analyses.”
When the ATLAS researchers combined the new mass measurement in the diphoton channel with the earlier mass measurement in the four-lepton channel, they obtained a Higgs boson mass of 125.11 GeV with an uncertainty of 0.11 GeV.
With a precision of 0.09%, this is the most precise measurement yet of this fundamental parameter.
“This very precise measurement is the result of the relentless investment of the ATLAS collaboration in improving the understanding of our data,” said ATLAS spokesperson Dr. Andreas Hoecker.
“Powerful reconstruction algorithms paired with precise calibrations are the determining ingredients of precision measurements.”
“The new measurement of the Higgs boson’s mass adds to the increasingly detailed mapping of this critical new sector of particle physics.”
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ATLAS Collaboration. 2023. Measurement of the Higgs boson mass with H→γγ decays in 140 fb−1 of s√=13 TeV pp collisions with the ATLAS detector. ATLAS-CONF-2023-036
