Measurement of the properties of Higgs boson production at $$ \sqrt{s} $$ = 13 TeV in the H → γγ channel using 139 fb−1 of pp collision data with the ATLAS experiment

Published for SISSA by Springer Received: July 4, 2022 Accepted: October 30, 2022 Published: July 11, 2023 The ATLAS collaboration E-mail: Abstract: Measurements of Higgs boson production cross-sections are carried out in the √ diphoton decay channel using 139 fb−1 of pp collision data at s = 13 TeV collected by the ATLAS experiment at the LHC. The analysis is based on the definition of 101 distinct signal regions using machine-learning techniques. The inclusive Higgs boson signal strength in the diphoton channel is measured to be 1.04+0.10 −0.09 . Cross-sections for gluon-gluon fusion, vectorboson fusion, associated production with a W or Z boson, and top associated production processes are reported. An upper limit of 10 times the Standard Model prediction is set for the associated production process of a Higgs boson with a single top quark, which has a unique sensitivity to the sign of the top quark Yukawa coupling. Higgs boson production is further characterized through measurements of Simplified Template Cross-Sections (STXS). In total, cross-sections of 28 STXS regions are measured. The measured STXS crosssections are compatible with their Standard Model predictions, with a p-value of 93%. The measurements are also used to set constraints on Higgs boson coupling strengths, as well as on new interactions beyond the Standard Model in an effective field theory approach. No significant deviations from the Standard Model predictions are observed in these measurements, which provide significant sensitivity improvements compared to the previous ATLAS results. Keywords: Hadron-Hadron Scattering , Higgs Physics ArXiv ePrint: 2207.00348 Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3 . https://doi.org/10.1007/JHEP07(2023)088 JHEP07(2023)088 Measurement of the properties of Higgs boson √ production at s = 13 TeV in the H → γγ channel using 139 fb−1 of pp collision data with the ATLAS experiment Contents 1 2 ATLAS detector 2 3 Data and simulation samples 3.1 Data 3.2 Simulation samples 3 3 4 4 Event reconstruction and selection 4.1 Photon reconstruction and identification 4.2 Event selection and selection of the diphoton primary vertex 4.3 Reconstruction and selection of hadronic jets, b-jets, leptons, top quarks and missing transverse momentum 6 6 7 8 5 Design of the measurement 5.1 Overview 5.2 Categorization 9 9 10 6 Modelling of diphoton mass distributions 6.1 Modelling of the signal shape 6.2 Modelling of the continuum background shape 20 20 21 7 Systematic uncertainties 7.1 Experimental systematic uncertainties 7.2 Theory modelling uncertainties 26 26 27 8 Results 8.1 Statistical procedure 8.2 Overall Higgs boson signal strength 8.3 Production cross-sections 8.4 Cross-sections in STXS regions 28 29 30 30 34 9 Interpretation of the results in the κ-framework 40 10 Interpretation of the results in the Standard Model effective field theory framework 42 10.1 Interpretation framework 42 10.2 Measurements of single SMEFT parameters 44 10.3 Simultaneous measurement of SMEFT parameters 46 11 Conclusion 53 –i– JHEP07(2023)088 1 Introduction A Additional production mode cross-section and STXS measurement results 54 B Additional κ-framework interpretations B.1 Parameterization of STXS cross-section parameters and the H→ γγ branching ratio B.2 Parameterization with universal coupling modifiers to weak gauge bosons and fermions B.3 Generic parameterization using ratios of coupling modifiers 57 C Effective field theory interpretation C.1 Measurement of single SMEFT parameters C.2 Simultaneous measurement of SMEFT parameters C.3 Results including SMEFT propagator corrections 61 61 63 67 The ATLAS collaboration 80 58 59 Introduction The experimental characterization of the Higgs boson discovered by the ATLAS and CMS experiments [1, 2] is not only crucial for our understanding of the mechanism of electroweak symmetry breaking [3–5] but also for providing insight into physics beyond the Standard Model (SM). Despite a small Higgs boson to diphoton (H → γγ) branching ratio of (0.227 ± 0.007)% [6] in the SM, measurements in the diphoton final state have yielded some of the most precise determinations of Higgs boson properties [7–11], thanks to the excellent performance of photon reconstruction and identification with the ATLAS detector. The signature of the Higgs boson in the diphoton final state is a narrow peak in the diphoton invariant mass (mγγ ) distribution with a width consistent with detector resolution, rising above a smoothly falling background. The diphoton mass resolution for such a resonance is typically between 1 GeV and 2 GeV, depending on the event kinematics. The mass and event yield of the Higgs boson signal can be extracted through fits of the mγγ distribution. Properties of the Higgs boson have been studied extensively in the diphoton final state by the ATLAS and CMS experiments [10–19]. This paper reports measurements of Higgs boson production cross-sections in the diphoton decay channel, using a data set of √ proton-proton collisions at s = 13 TeV collected by the ATLAS experiment from 2015 to 2018, a period known as Run 2 of the Large Hadron Collider (LHC). Its integrated luminosity is 139 fb−1 [20, 21], a roughly fourfold increase compared to the previous ATLAS publication of such measurements in the diphoton channel [10]. Apart from the increased data set size, the most significant improvement in the sensitivity is due to redesigned and refined event selection and categorization techniques compared to ref. [10]. Uncertainties on the modeling of continuum background have been reduced through the use of a smoothing procedure based on a Gaussian kernel [22]. The performance of the reconstruction and selection of the physics objects used in these measurements has also been generally improved. –1– JHEP07(2023)088 1 57 2 ATLAS detector The ATLAS detector [30] at the LHC covers nearly the entire solid angle around the collision point.1 It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroidal magnets. The inner-detector system (ID) is immersed in a 2 T axial magnetic field and provides charged-particle tracking in the range |η| < 2.5. The high-granularity silicon pixel detector 1 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the z-axis along the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upwards. Cylindrical coordinates (r, ϕ) are used in the transverse plane, ϕ being the azimuthal angle around the z-axis. The pseudorapidity is p defined in terms of the polar angle θ as η = − ln tan(θ/2). Angular distance is measured in units of ∆R ≡ (∆η)2 + (∆ϕ)2 . –2– JHEP07(2023)088 The analysis is optim (...truncated)