Collider Cross Talk

Unveiling the polarisation of weak bosons in LHC processes

by Giovanni Pelliccioli (Max-Planck-Institut für Physik), Luka Selem (Centre National de la Recherche Scientifique (FR))

4/2-011 - TH common room (CERN)

4/2-011 - TH common room


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Accessing the polarisation state of weak bosons represents a crucial step to improve our understanding of the electroweak-symmetry-breaking mechanism that is realised in nature. The pioneering ATLAS and CMS measurements in di-boson inclusive production and scattering, as well as the recent efforts in the theory community, have paved the way to a novel approach to investigate the polarisation structure of multi-boson processes, relying on data fits with polarised-signal templates. In this cross talk, we will retrace the ATLAS measurement of joint polarisation fractions in inclusive WZ production (Phys. Lett. B 843 (2023) 137895, arXiv:2211.09435 [hep-ex]), focusing on the analysis strategy and the theoretical modelling. We will also address possible refinements of the WZ analysis, in lights of recent developments in the Monte Carlo automation of polarised signals and in machine-learning applications for polarisation extraction.

Luka Selem (ATLAS) is an experimentalist member of the ATLAS Collaboration. He got his PhD in 2022 at LAPP (Annecy, France) working on diboson polarisation in the WZ channel. This work resulted in the first joint-polarisation measurement at the LHC, reported by ATLAS in 2022. He is now a postdoc at LPSC (Grenoble, France) working on an exotic search for emerging jets as a sign of a dark QCD sector.

Giovanni Pelliccioli (theory) is a post-doc fellow at the Max-Planck Institute for Physics in Garching. After obtaining the PhD in 2019 at the University of Torino, he held a first post-doc position at the University of Würzburg until 2022. He mostly works on higher-order QCD and electroweak corrections to collider processes, and is especially interested in the phenomenology of weak-boson polarisations in multi-boson LHC signatures.