2949678 20260511142404.0 oai:cds.cern.ch:2949678 cerncds:FULLTEXT ATL-PHYS-PROC-2025-118 eng ATL-COM-PHYS-2025-1006 The ATLAS collaboration Higgs Boson CP Properties and Effective Field Theory Measurements from the ATLAS Experiment at the LHC 2025 Geneva CERN 25 Nov 2025 5 p 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. preprint CC BY 4.0 https://creativecommons.org/licenses/by/4.0/ preprint CERN 2025 PROC CERN CDS-Invenio WebSubmit For annual report SzGeCERN Particle Physics - Experiment SzGeCERN Physics CERN Higgs CP CERN Effective Field Theory CERN New Physics CERN ATLAS CERN LHC CERN HIGGS CERN INTNOTE PRIVATLAS INTNOTEATLASPUBL CERN LHC ATLAS PH-EP ATLAS Collaboration C25-08-25.1 http://cds.cern.ch/record/2948900 Original Communication (restricted to ATLAS) 2797720 689739 http://cds.cern.ch/record/2949678/files/ATL-PHYS-PROC-2025-118.pdf Stamped by WebSubmit: 25/11/2025 haijun.yang@cern.ch haijun.yang@sjtu.edu.cn n 202570 91 2939468 madison20250825 PUBLIC 000788796CER INTNOTEATLASPUBL ConferencePaper