Over the past 11 years since its discovery at the Large Hadron Collider (LHC), the Higgs boson has become a crucial window into understanding the fundamental structure of our universe. Physicists use precise measurements of this elusive particle to test the Standard Model, which currently serves as the best explanation for the world of particles and their interactions.
At the recent Lepton Photon Conference, the ATLAS collaboration presented their latest achievement in measuring the mass of the Higgs boson with unprecedented accuracy. The mass of the Higgs boson is not predicted by the Standard Model, so experimental measurements are essential. This value determines how the Higgs boson interacts with other elementary particles and itself. Knowing this fundamental parameter precisely allows physicists to compare their measurements with Standard Model predictions. Any deviations could indicate the presence of new phenomena yet to be discovered. Additionally, the Higgs boson’s mass plays a crucial role in the evolution and stability of the vacuum in our universe.
Over time, both the ATLAS and CMS collaborations have been steadily improving their measurements of the Higgs boson’s mass since its initial discovery. The latest ATLAS measurement combines two results: one based on the particle’s decay into two high-energy photons (the “diphoton channel”) and another from its decay into four leptons (the “four-lepton channel”).
The new measurement from the diphoton channel, using data from both Run 1 and Run 2 of the LHC, reveals a Higgs boson mass of 125.22 billion electronvolts (GeV) with a remarkable uncertainty of only 0.14 GeV. This level of precision, 0.11%, represents the most accurate measurement to date of the Higgs boson’s mass from a single decay channel.
The improvement in this result comes from the combined use of the complete ATLAS Run 2 data set, which reduced statistical uncertainty by half, and significant advancements in the calibration of photon energy measurements, decreasing systematic uncertainty nearly fourfold to 0.09 GeV.
Stefano Manzoni, the convener of the ATLAS electron-photon calibration subgroup, emphasizes the critical role of advanced calibration techniques for achieving this level of precision. These techniques, developed over several years with a deep understanding of the ATLAS detector, will also benefit future analyses.
By combining the new diphoton channel measurement with the earlier four-lepton channel measurement, the ATLAS researchers arrived at a Higgs boson mass of 125.11 GeV with an uncertainty of 0.11 GeV. This represents the most precise measurement ever of this fundamental parameter, boasting a precision of 0.09%.
Andreas Hoecker, ATLAS spokesperson, credits this extraordinary achievement to the relentless efforts of the ATLAS collaboration in improving data understanding. Powerful reconstruction algorithms coupled with precise calibrations have been instrumental in achieving these precision measurements, further enriching our understanding of particle physics’ critical new frontier.