CMS-PAS-TOP-24-012

CMS-PAS-TOP-24-012
Search for $ CP $ violation in events with top quarks and Z bosons
CMS Collaboration
28 March 2025

Abstract: A search for the violation of the charge-parity ($ CP $) symmetry in the production of top quarks in association with Z bosons is presented, using events with three charged leptons and additional jets. For the first time in this final state, observables that are odd under the $ CP $ transformation are employed. Also for the first time, physics-informed machine learning techniques are used to construct these observables. While standard model (SM) processes are predicted to be symmetrically distributed around zero on these observables, $ CP $-violating modifications of the SM would introduce asymmetries. Two $ CP $-odd operators $ c_{\mathrm{tW}}^{\mathrm{I}} $ and $ c_{\mathrm{tZ}}^{\mathrm{I}} $ in the SM effective field theory are considered that may modify the interactions between top quarks and electroweak bosons. The search is performed in a sample of proton-proton collision data collected by the CMS experiment at the CERN LHC in 2016-2018 at a center-of-mass energy of 13 TeV and in 2022 at 13.6 TeV, corresponding to a total integrated luminosity of 175 fb$ ^{-1} $. The obtained results are consistent with the SM prediction within two standard deviations, and exclusion limits of $ -$2.7 $ < c_{\mathrm{tW}}^{\mathrm{I}} < $ 2.5 and $ -$0.2 $ < c_{\mathrm{tZ}}^{\mathrm{I}} < $ 2.0 are set at 95% confidence level.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here.

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