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CP violation angles from H→ττ decays at the FCC-ee

S. Giappichini, M. Klute, and M. Presilla*

  • *Contact author: matteo.presilla@cern.ch
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Phys. Rev. D 114, 032013 – Published 25 August, 2026

DOI: https://doi.org/10.1103/b71w-xrqg

Abstract

Measuring charge-parity (CP) violation in Higgs-fermion interactions is a key target of future precision Higgs programs. The decay H→ττ is particularly sensitive to the CP structure of the Higgs Yukawa coupling via τ spin correlation, while the clean environment of e+e− collisions at the Future Circular Collider (FCC) enables accurate reconstruction of CP-sensitive observables. In this letter, we study the sensitivity of FCC-ee to the Higgs CP state using H→ττ events produced in associated ZH production at s=240  GeV. In the anomalous-coupling parametrization, we project a precision of Δϕττ=±2.5° at 68% CL, with the dominant contribution arising from one-prong hadronic τ decays. We further interpret the analysis in the effective field theory framework, deriving expected limits on the CP-odd operators, and compare them with electron and magnetic dipole moment measurements and the anomalous-coupling approach.

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References (60)

  1. J. Altmann et al., ECFA Higgs, electroweak, and top factory study, CERN Yellow Report Monographs, Report No. CERN-2025-005, (, 2025).
  2. J. de Blas et al., Physics briefing book: Input for the 2026 update of the European strategy for particle physics, 10.17181/CERN.35CH.2O2P (2025).
  3. A. Abada et al. (FCC Collaboration), FCC-ee: The lepton collider: Future circular collider conceptual design report volume 2, Eur. Phys. J. Special Topics 228, 261 (2019).
  4. M. Benedikt et al. (FCC Collaboration), Future circular collider feasibility study report: Volume 2, accelerators, technical infrastructure and safety, Eur. Phys. J. Special Topics 234, 5713 (2025).
  5. G. Arduini, F. Bordry, R. Brinkmann, P. Burrows, K. Desch, S. Farrington, F. Gianotti, K. Hanagaki, N. Holtkamp, J. Keintzel, B. Kilminster, T. Lesiak, L. Rivkin, F. Sabatié, M.  Tuts, and A. Zoccoli, Assessment of large-scale accelerator projects at CERN—Report of ESG WG2a, Technical Report No. CERN-ESU-ESG-WG2a-full-report, CERN, Geneva, 2025.
  6. A. Abada et al. (FCC Collaboration), FCC physics opportunities: Future circular collider conceptual design report volume 1, Eur. Phys. J. C 79, 474 (2019).
  7. M. Benedikt et al. (FCC Collaboration), Future circular collider feasibility study report: Volume 1, physics, experiments, detectors, Eur. Phys. J. C 85, 1468 (2025).
  8. M. Selvaggi, A. Blondel, and J. Eysermans (FCC Collaboration), Prospects in electroweak, Higgs and top physics at FCC, 10.17181/n78xk-qcv56 (2025).
  9. G. Aad et al. (ATLAS Collaboration), Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector, Eur. Phys. J. C 75, 476 (2015); 76, 152(E) (2016).
  10. M. Aaboud et al. (ATLAS Collaboration), Measurement of the Higgs boson coupling properties in the H→ZZ*→4ℓ decay channel at s=13  TeV with the ATLAS detector, J. High Energy Phys. 03 (2018) 095.
  11. M. Aaboud et al. (ATLAS Collaboration), Measurements of Higgs boson properties in the diphoton decay channel with 36  fb−1 of pp collision data at s=13  TeV with the ATLAS detector, Phys. Rev. D 98, 052005 (2018).
  12. G. Aad et al. (ATLAS Collaboration), Test of CP-invariance of the Higgs boson in vector-boson fusion production and in its decay into four leptons, J. High Energy Phys. 05 (2024) 105.
  13. V. Khachatryan et al. (CMS Collaboration), Combined search for anomalous pseudoscalar HVV couplings in VH(H→bb¯) production and H→VV decay, Phys. Lett. B 759, 672 (2016).
  14. A. M. Sirunyan et al. (CMS Collaboration), Measurements of the Higgs boson width and anomalous HVV couplings from on-shell and off-shell production in the four-lepton final state, Phys. Rev. D 99, 112003 (2019).
  15. A. M. Sirunyan et al. (CMS Collaboration), Constraints on anomalous HVV couplings from the production of Higgs bosons decaying to τ lepton pairs, Phys. Rev. D 100, 112002 (2019).
  16. C. E. M. Wagner, Electroweak baryogenesis and Higgs physics, Lett. High Energy Phys. 2023, 466 (2023).
  17. H.-K. Guo, Y.-Y. Li, T. Liu, M. Ramsey-Musolf, and J. Shu, Lepton-flavored electroweak baryogenesis, Phys. Rev. D 96, 115034 (2017).
  18. S. F. King, M. Muhlleitner, R. Nevzorov, and K. Walz, Exploring the CP-violating NMSSM: EDM constraints and phenomenology, Nucl. Phys. B901, 526 (2015).
  19. A. V. Gritsan et al., Snowmass white paper: Prospects of CP-violation measurements with the Higgs boson at future experiments, arXiv:2205.07715.
  20. R. Harnik, A. Martin, T. Okui, R. Primulando, and F. Yu, Measuring CP violation in h→τ+τ− at colliders, Phys. Rev. D 88, 076009 (2013).
  21. J. Brod, U. Haisch, and J. Zupan, Constraints on CP-violating Higgs couplings to the third generation, J. High Energy Phys. 11 (2013) 180.
  22. W. Buchmüller and D. Wyler, Effective Lagrangian analysis of new interactions and flavour conservation, Nucl. Phys. B268, 621 (1986).
  23. B. Grzadkowski, M. Iskrzyński, M. Misiak, and J. Rosiek, Dimension-six terms in the standard model Lagrangian, J. High Energy Phys. 10 (2010) 085.
  24. S. Das Bakshi, J. Chakrabortty, C. Englert, M. Spannowsky, and P. Stylianou, CP violation at ATLAS in effective field theory, Phys. Rev. D 103, 055008 (2021).
  25. S. D. Bakshi, J. Chakrabortty, C. Englert, M. Spannowsky, and P. Stylianou, Landscaping CP-violating BSM scenarios, Nucl. Phys. B975, 115676 (2022).
  26. S.-F. Ge, G. Li, P. Pasquini, and M. J. Ramsey-Musolf, CP-violating Higgs di-tau decays: Baryogenesis and Higgs factories, Phys. Rev. D 103, 095027 (2021).
  27. E. Fuchs, M. Losada, Y. Nir, and Y. Viernik, CP violation from τ, t and b dimension-6 Yukawa couplings—interplay of baryogenesis, EDM and Higgs physics, J. High Energy Phys. 05 (2020) 056.
  28. J. De Vries, M. Postma, and J. van de Vis, The role of leptons in electroweak baryogenesis, J. High Energy Phys. 04 (2019) 024.
  29. K. Desch, A. Imhof, Z. Was, and M. Worek, Probing the CP nature of the Higgs boson at linear colliders with tau spin correlations: The case of mixed scalar—pseudoscalar couplings, Phys. Lett. B 579, 157 (2004).
  30. Y.-S. Tsai, Decay correlations of heavy leptons in e+e−→l+l−, Phys. Rev. D 4, 2821 (1971); 13, 771(E) (1976).
  31. B. Grzadkowski and J. F. Gunion, Using decay angle correlations to detect CP violation in the neutral Higgs sector, Phys. Lett. B 350, 218 (1995).
  32. A. Tumasyan et al. (CMS Collaboration), Analysis of the CP structure of the Yukawa coupling between the Higgs boson and τ leptons in proton-proton collisions at s=13  TeV, J. High Energy Phys. 06 (2022) 012.
  33. G. Aad et al. (ATLAS Collaboration), Measurement of the CP properties of Higgs boson interactions with τ-leptons with the ATLAS detector, Eur. Phys. J. C 83, 563 (2023).
  34. W. Esmail, A. Hammad, M. Nojiri, and C. Scherb, Testing CP properties of the Higgs boson coupling to τ leptons with heterogeneous graphs, J. High Energy Phys. 04 (2025) 083.
  35. M. Aaboud et al. (ATLAS Collaboration)Probing the CP nature of the Higgs boson coupling to τ leptons at HL-LHC, Technical Report No. ATL-PHYS-PUB-2019-008, CERN, 2019.
  36. D. Jeans and G. W. Wilson, Measuring the CP state of tau lepton pairs from Higgs decay at the ILC, Phys. Rev. D 98, 013007 (2018).
  37. S. Giappichini, M. Klute, M. Presilla, X. Zuo, and M. Cepeda, Measurements of H→ττ cross-section at FCC-ee, arXiv:2601.11383.
  38. V. Khachatryan et al. (CMS Collaboration), Constraints on the spin-parity and anomalous HVV couplings of the Higgs boson in proton collisions at 7 and 8 TeV, Phys. Rev. D 92, 012004 (2015).
  39. A. Askew, P. Jaiswal, T. Okui, H. B. Prosper, and N. Sato, Prospect for measuring the CP phase in the hττ coupling at the LHC, Phys. Rev. D 91, 075014 (2015).
  40. C. Bierlich et al., A comprehensive guide to the physics and usage of pythia 8.3, SciPost Phys. Codebases 2022, 8 (2022).
  41. I. Brivio, Y. Jiang, and M. Trott, The smeftsim package, theory and tools, J. High Energy Phys. 12 (2017) 070.
  42. I. Brivio, smeftsim 3.0—A practical guide, J. High Energy Phys. 04 (2021) 073.
  43. I. Brivio, S. Dawson, J. de Blas, G. Durieux, P. Savard, A. Denner, A. Freitas, C. Hays, B. Pecjak, and A. Vicini, Electroweak input parameters, arXiv:2111.12515.
  44. J. Alwall, R. Frederix, S. Frixione, V. Hirschi, F. Maltoni, O. Mattelaer, H. S. Shao, T. Stelzer, P. Torrielli, and M. Zaro, The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations, J. High Energy Phys. 07 (2014) 079.
  45. K. Hagiwara, T. Li, K. Mawatari, and J. Nakamura, taudecay: A library to simulate polarized tau decays via feynrules and madgadraph5, Eur. Phys. J. C 73, 2489 (2013).
  46. W. Kilian, T. Ohl, and J. Reuter, whizard: Simulating multi-particle processes at LHC and ILC, Eur. Phys. J. C 71, 1742 (2011).
  47. M. Moretti, T. Ohl, and J. Reuter, O’Mega: An optimizing matrix element generator, arXiv:hep-ph/0102195.
  48. T. Sjostrand, S. Mrenna, and P. Z. Skands, pythia 6.4 physics and manual, J. High Energy Phys. 05 (2006) 026.
  49. J. de Favereau, C. Delaere, P. Demin, A. Giammanco, V. Lemaître, A. Mertens, and M. Selvaggi (DELPHES 3 Collaboration), delphes 3, A modular framework for fast simulation of a generic collider experiment, J. High Energy Phys. 02 (2014) 057.
  50. M. Abbrescia et al. (IDEA Study Group), The IDEA detector concept for FCC-ee, arXiv:2502.21223.
  51. M. Cacciari, G. P. Salam, and G. Soyez, fastjet user manual, Eur. Phys. J. C 72, 1896 (2012).
  52. P. Konar and A. K. Swain, Reconstructing semi-invisible events in resonant tau pair production from Higgs, Phys. Lett. B 757, 211 (2016).
  53. D. Jeans, Tau lepton reconstruction at collider experiments using impact parameters, Nucl. Instrum. Methods Phys. Res., Sect. A 810, 51 (2016).
  54. S. Berge and W. Bernreuther, Determining the CP parity of Higgs bosons at the LHC in the tau to 1-prong decay channels, Phys. Lett. B 671, 470 (2009).
  55. S. Berge, W. Bernreuther, and S. Kirchner, Prospects of constraining the Higgs boson’s CP nature in the tau decay channel at the LHC, Phys. Rev. D 92, 096012 (2015).
  56. G. R. Bower, T. Pierzchala, Z. Was, and M. Worek, Measuring the Higgs boson’s parity using τ→ρυ, Phys. Lett. B 543, 227 (2002).
  57. S. Berge, W. Bernreuther, and S. Kirchner, Determination of the Higgs CP-mixing angle in the tau decay channels at the LHC including the Drell–Yan background, Eur. Phys. J. C 74, 3164 (2014).
  58. A. Hayrapetyan et al. (CMS Collaboration), The CMS statistical analysis and combination tool: COMBINE, Comput. Softw. Big Sci. 8, 19 (2024)..
  59. S. M. Barr and A. Zee, Electric dipole moment of the electron and of the neutron, Phys. Rev. Lett. 65, 21 (1990); 65, 2920(E) (1990).
  60. N. Košnik, A. Palavrić, and A. Smolković, UV origins of CP-violating leptonic Yukawa couplings, Phys. Rev. D 112, 095046 (2025).

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Phys. Rev. D 114, 032013– Published 25 August, 2026
  • Received 21 February 2026
  • Accepted 31 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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