Journal Article

PUBDB-2026-00383

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Determination of $\mathcal{C}\mathcal{P}$-violating HZZ interaction with polarised beams at the ILC

Li, C. (Corresponding author) ; Moortgat-Pick, G. (Corresponding author)DESY*

2025
Springer Heidelberg

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Please use a persistent id in citations: doi:10.1140/epjc/s10052-025-13828-4  doi:10.3204/PUBDB-2026-00383

Abstract: We study possible ${\mathcal{C}\mathcal{P}}$-violation effects of the 125 GeV Higgs to Z boson coupling at the 250 GeV ILC with transverse and longitudinal beam polarisation via the process $e^+ e^- \rightarrow HZ \rightarrow H \mu ^-\mu ^+$. We explore the azimuthal angular distribution of the muon pair from the Z boson decay, and constructe ${\mathcal{C}\mathcal{P}}$-odd observables sensitive to ${\mathcal{C}\mathcal{P}}$-violation effects, where we derived this observable both by analytical calculations and by Whizard simulations. Particularly, we can construct two ${\mathcal{C}\mathcal{P}}$-odd observables with the help of transversely-polarised initial beams and improve the statistical significance of ${\mathcal{C}\mathcal{P}}$-violation effects by combining two measurements. We defined the asymmetries between the signal regions with different signs of the ${\mathcal{C}\mathcal{P}}$-odd observables, and determine the ${\mathcal{C}\mathcal{P}}$-violation effect by comparing with the SM 95% CL upper bound. In this paper, we setup a scenario which assumes that the total cross-section is always fixed while ${\mathcal{C}\mathcal{P}}$-violation is varying, and such a scenario helps us to determine the intrinsic ${\mathcal{C}\mathcal{P}}$-mixing angle limit around $|\xi _{\mathcal{C}\mathcal{P}}|\sim 0.03~{\operatorname {rad}}$ with (90%, 40%) polarised electron-positron beams and 5 $\hbox {ab}^{-1}$ integrated luminosity. In addition, we determine the ${\mathcal{C}\mathcal{P}}$-odd coupling limit $|\widetilde{c}_{HZZ}|\sim 0.01$ as well, where we suppose that the SM tree-level cross-section is fixed and the ${\mathcal{C}\mathcal{P}}$-violation is the varying additional contribution. Comparing with the analysis with unpolarised beams, the sensitivity to the ${\mathcal{C}\mathcal{P}}$-violation effect can be improved by transverse or longitudinal polarisation.

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Contributing Institute(s):

1. Technol. zukünft. Teilchenph. Experim. (FTX)

Research Program(s):

1. DFG project G:(GEPRIS)390833306 - EXC 2121: Das Quantisierte Universum II (390833306) (390833306)
2. 611 - Fundamental Particles and Forces (POF4-611) (POF4-611)

Experiment(s):

1. Facility (machine) ILC

Appears in the scientific report 2025

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Database coverage:
; ; ; ; ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; DOAJ Seal ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; SCOAP3 sponsored Journal ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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