No Time to Be Transverse: Probing Electroweak Symmetry Breaking with Longitudinal Weak Bosons at ATLAS

by Lailin Xu (University of Science and Technology of China (CN))

Tuesday 28 Jul 2026, 11:00 → 12:00 Europe/Zurich

503/1-001 - Council Chamber (CERN)

The mechanism of electroweak symmetry breaking (EWSB), responsible for generating the masses of the W and Z bosons, also gives rise to their longitudinal polarization states. Measurements of weak-boson polarization therefore provide one of the most direct experimental probes of the EWSB mechanism and offer powerful sensitivity to physics beyond the Standard Model. Although long considered beyond reach at hadron colliders because of the small production rates and the challenge of reconstructing polarization states, such measurements have recently become possible thanks to the large LHC datasets, advances in machine-learning techniques, and increasingly precise theoretical predictions.

This seminar presents two recent ATLAS measurements of weak-boson polarization in diboson production, based on the full Run 2 dataset together with part of the Run 3 dataset, corresponding to an integrated luminosity of about 300 fb⁻¹. The first targets the simultaneous production of two longitudinally polarized Z bosons, while the second probes the longitudinal component of the Z boson in electroweak WZjj production. Both analyses exploit the clean leptonic decays of the gauge bosons into electrons and muons and employ machine-learning techniques to maximize sensitivity. The resulting polarization fractions and fiducial cross sections are compared with state-of-the-art Standard Model predictions, highlighting the growing power of weak-boson polarization as a precision probe of the electroweak sector.

 

 

Coffee will be served at 10h30