The CMS collaboration at CERN has announced the most precise measurement yet of the effective electroweak mixing angle at a hadron collider. Presented at the recent Rencontres de Moriond conference, this result matches the accuracy achieved previously only at dedicated electron-positron colliders.
The electroweak mixing angle is a fundamental parameter of the Standard Model, describing how the unified electroweak force splits into the electromagnetic and weak nuclear forces. Precise measurements of this key value allow stringent tests of the Standard Model’s predictive power and potential deviations that could hint at new physics.
While past measurements at CERN’s LEP and Stanford’s SLD electron-positron colliders disagreed, the new CMS result from LHC proton-proton collision data aligns impressively with the theoretical prediction. This represents a leap in precision for hadron collider experiments like CMS and ATLAS.
“This result shows that precision physics can be carried out at hadron colliders,” stated CMS spokesperson Patricia McBride. “The analysis had to handle the challenging environment of LHC Run 2, with an average of 35 simultaneous proton-proton collisions. This paves the way for more precision physics at the High-Luminosity LHC.”
The measurement derives from analyzing the angular distributions of produced electron and muon pairs in 137 inverse femtobarns of 13 TeV proton-proton collision data collected from 2016-2018.
Achieving this level of precision in the hostile hadron collision environment required overcoming immense backgrounds and analyzing an enormous dataset of around 11 quadrillion collisions.
Historically, electron-positron colliders like LEP offered an ideal clean environment for such exacting electroweak measurements. Replicating that precision in LHC’s proton-proton collisions was considered near impossible until this CMS result.
Precise tests of fundamental Standard Model parameters have long been the domain of electron-positron machines. This achievement demonstrates the potential for CERN’s hadron colliders to extend that legacy with measurements that could uncover deviations from theoretical predictions, providing glimpses of new physics waiting to be discovered.
