| ATLAS Note | |
| Report number | ATL-PHYS-PROC-2025-118 |
| Title | Higgs Boson CP Properties and Effective Field Theory Measurements from the ATLAS Experiment at the LHC |
| Corporate Author(s) | The ATLAS collaboration |
| Collaboration | ATLAS Collaboration |
| Publication | 2025 |
| Imprint | 25 Nov 2025 |
| Number of pages | 5 |
| In: | The 32nd International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 2025), Madison, Wisconsin, Us, 25 - 29 Aug 2025 |
| Subject category | Particle Physics - Experiment |
| Accelerator/Facility, Experiment | CERN LHC ; ATLAS |
| Free keywords | Higgs CP ; Effective Field Theory ; New Physics ; ATLAS ; LHC ; HIGGS |
| Abstract | This paper presents a concise overview of the Higgs boson's CP properties and constraints on Effective Field Theory (EFT) operators, derived from the ATLAS experiment at the Large Hadron Collider (LHC). Using proton-proton collision data with integrated luminosities of up to 140 fb$^{-1}$ at $\sqrt{s} = 13$ TeV, we systematically probe the CP nature of the Higgs boson's couplings to fermions ($\tau$ leptons, bottom quarks, and top quarks) and bosons ($W$, $Z$, and $\gamma$) across diverse decay final states. The EFT framework is used to parameterize Beyond the Standard Model (BSM) effects via dimension-6 operators, enabling model-independent constraints on CP violation and new physics scales. The main focus is comparison of measurement characteristics and sensitivity across different final states: (1) $H \to \tau\tau$ (semileptonic/hadronic decays) for light fermion couplings, (2) $H \to \gamma\gamma$ and $H \to bb$ in $t\bar{t}H/tH$ processes for heavy fermion couplings, (3) $H \to WW^* \to l\nu l\nu$, $H \to ZZ^* \to 4l$, and vector boson fusion (VBF) $H \to \tau\tau/\gamma\gamma$ for boson couplings, and (4) double Higgs ($HH$) production for self-couplings. All measurements are consistent with the Standard Model (SM) prediction of a CP-even Higgs boson ($J^{CP} = 0^{++}$), with no evidence of CP violation. The most stringent constraint on the CP-odd EFT parameter $c_{H\tilde{W}}$ is obtained from VBF $H \to \tau\tau$ ($c_{H\tilde{W}} \in [-0.23, 0.70]$ at 95\% CL), highlighting the unique sensitivity of this channel. Complementary constraints from other final states reinforce the robustness of SM consistency and provide a foundation for future searches. |
| Copyright/License | preprint: © 2025-2026 CERN (License: CC BY 4.0) |
Record created 2025-11-25, last modified 2026-05-11
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