https://doi.org/10.1140/epjc/s10052-025-14503-4
Regular Article - Theoretical Physics
Leveraging intermediate resonances to probe CP violation at colliders
1
Physics and Astronomy Department, Northwestern University, Evanston, IL, USA
2
Theoretical Physics Department, Fermilab, P.O. Box 500, 60510, Batavia, IL, USA
3
Uichang District Office, 468, Dogye-dong Uichang-gu, 51381, Changwon, South Korea
4
Physics Department, University of Notre Dame, 225 Nieuwland Science Hall, 46556, Notre Dame, IN, USA
Received:
10
February
2025
Accepted:
7
July
2025
Published online:
28
July
2025
We explore the phenomenological impact of interference in tree-level contributions to three-body final states in 
scattering processes. This work introduces a novel search strategy leveraging asymmetries to enable sensitivity to CP-violating effects in less well-explored regions of phase space. Analytically, we demonstrate the effectiveness of this observable in probing interference between Standard Model charged-current decays and effective left-handed vector interactions, illustrated in a toy model featuring a scalar leptoquark, 
. Numerically, we apply this framework to studying the process 
; unlike traditional high-
searches or “bump hunts”, this approach utilizes an intermediate energy regime – where new physics is neither light enough to be produced on shell or heavy enough to justify an effective field theory treatment. A proof-of-principle analysis at parton level demonstrates a percent-level asymmetry, with sensitivity also to BSM weak-CP phase. While the specific phase sensitivity is diminished at particle level due to showering and detector effects, a machine learning classifier can recover sensitively to the presence of SM-BSM interference, significantly outperforming standard analysis methods. Notably discrimination between BSM signal and SM background could be achieved at the 2
level for the current LHC dataset and 8 at the High-Luminosity LHC. Moreover, this asymmetry observable as defined can also be more broadly applied to other searches for CP-violation in processes in present and future collider environments.
© The Author(s) 2025
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Funded by SCOAP3.
