Combining measurements from two Higgs boson decay channels, the CMS experiment determines the particle’s mass to be 125.065 GeV, with an uncertainty of just 88 MeV. This is the most precise measurement of the Higgs boson mass achieved by a single experiment to date.
The mass of the Higgs boson is a fundamental parameter in the Standard Model of particle physics, our best description of elementary particles and their interactions. It is a free parameter of the Standard Model that must be determined experimentally. Measuring it with greater precision improves the accuracy of theoretical predictions for Higgs boson properties and interactions. Comparing these predictions with observations also tests the Standard Model and could reveal signs of new physics.
The new CMS result combines complementary measurements from two decay channels: one in which the Higgs boson decays into two photons (H → γγ), and another in which it decays into two Z bosons, each of which can subsequently decay into a pair of leptons, yielding four electrons, muons, or one pair of each (H → ZZ → 4l). Although these decay processes are relatively rare, they offer particularly clean experimental signatures, allowing physicists to reconstruct the Higgs boson mass with high precision. By combining the two channels, CMS can reduce the measurement uncertainty even more.
The combination includes measurements that use proton–proton collision data collected at center-of-mass energies of 7, 8 and 13 TeV. The resulting mass measurement has a precision of 0.07%. Achieving this level of precision requires careful calibration of the detector, detailed modelling of the relevant physical processes, and rigorous evaluation of the various sources of uncertainty.
This result also paves the way for a future combination with measurements from the ATLAS experiment, which studies the same particle at the LHC independently. Together, they could establish an even more precise reference value for the Higgs boson mass, supporting a wide range of particle physics studies.
Above: CMS measurements of the Higgs boson mass in the H → γγ and H → ZZ → 4l decay channels, and their combined result. Smaller uncertainty bars indicate more precise measurements.
“This combination brings together years of careful measurements by CMS, building on the excellent work of many colleagues,” says Chenguang Zhang from the Institute of High-Energy Physics, Chinese Academy of Sciences (IHEP-CAS). “Looking ahead, combining our results with those from ATLAS could further sharpen our knowledge of the Higgs boson mass and support future studies of its properties and tests of the Standard Model.”
Written by: Chenguang Zhang, for the CMS Collaboration
Edited by: Muhammad Ansar Iqbal
Read more about these results:
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CMS Physics Analysis Summary (HIG-26-010): "Combined measurement of the Higgs boson mass in the H → ZZ → 4ℓ and H → γγ decay channels using pp collision data at √s = 7, 8, and 13 TeV"
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