Measurements of gluon-gluon fusion and vector-boson fusion Higgs boson productioncross-sections in the H→ W W * → eν µν decay channel in p p collisions at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration Higgs boson production cross-sections in proton-proton collisions are measured in the H→ WW * → eν µν decay channel. The proton-proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the AT-LAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb −1 . The product of the H→ WW * branching fraction times the gluon-gluon fusion and vector-boson fusion cross-sections are measured to be 11.4 +1.2 −1.1 (stat.) +1.8 −1.7 (syst.) pb and 0.50 +0.24 −0.22 (stat.) ± 0.17(syst.) pb, respectively, in agreement with Standard Model predictions.ATLAS is a particle detector designed to achieve a nearly full coverage in solid angle1 [5, 6]. 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 air-core toroidal magnets. The inner tracking detector (ID) is located in a 2 T magnetic field and is designed to measure charged-particle trajectories up to a pseudorapidity of |η| = 2.5. Surrounding the ID are electromagnetic and hadronic calorimeters, which use liquid argon (LAr) and lead absorber for the electromagnetic central and endcap calorimeters (|η| < 3.2), copper absorber for the hadronic endcap calorimeter (1.5 < |η| < 3.2), and scintillator-tile active material with steel absorber for the central (|η| < 1.7) hadronic calorimeter. The solid angle coverage is extended to |η| = 4.9 with forward copper/LAr and tungsten/LAr calorimeter modules. The muon spectrometer comprises separate trigger chambers within the range |η| < 2.4 and high-precision tracking chambers within the range |η| < 2.7, measuring the deflection of muons in a magnetic field generated by the three superconducting toroidal magnets. A two-level trigger system is used to select events [7].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 upward. Cylindrical coordinates (r, φ) are used in the transverse plane, φ being the azimuthal angle around the zaxis. The pseudorapidity is defined in terms of the polar angle θ as η = − ln tan(θ/2). The distance in (η,φ) coordinates, ∆R = ∆φ 2 + ∆η 2 , is also used to define cone sizes. Transverse momentum and energy are defined as p T = p sin θ and E T = E sin θ, respectively. Signal and background Monte Carlo predictionsHiggs boson production via ggF was simulated at next-to-next-to-leading-order (NNLO) accuracy in QCD using the P -B v2 NNLOPS program [8], with the PDF4LHC15 NNLO set of parton distribution functions (PDF) [9]. The simulation achieves NNLO accuracy for arbitrary inclusive gg → ...

This paper presents an analysis at next-to-next-to-leading order in the theory of quantum chromodynamics for the determination of a new set of proton parton distribution functions using diverse measurements in pp collisions at $$\sqrt{s} = 7$$ s = 7 , 8 and 13 TeV, performed by the ATLAS experiment at the Large Hadron Collider, together with deep inelastic scattering data from ep collisions at the HERA collider. The ATLAS data sets considered are differential cross-section measurements of inclusive $$W^{\pm }$$ W ± and $$Z/\gamma ^*$$ Z / γ ∗ boson production, $$W^{\pm }$$ W ± and Z boson production in association with jets, $$t\bar{t}$$ t t ¯ production, inclusive jet production and direct photon production. In the analysis, particular attention is paid to the correlation of systematic uncertainties within and between the various ATLAS data sets and to the impact of model, theoretical and parameterisation uncertainties. The resulting set of parton distribution functions is called ATLASpdf21.

A search for the Higgs boson decaying into a pair of charm quarks is presented. The analysis uses proton–proton collisions to target the production of a Higgs boson in association with a leptonically decaying W or Z boson. The dataset delivered by the LHC at a centre-of-mass energy of "Equation missing" and recorded by the ATLAS detector corresponds to an integrated luminosity of 139 $$\text{ fb}^{-1}$$ fb - 1 . Flavour-tagging algorithms are used to identify jets originating from the hadronisation of charm quarks. The analysis method is validated with the simultaneous measurement of WW, WZ and ZZ production, with observed (expected) significances of 2.6 (2.2) standard deviations above the background-only prediction for the $$(W/Z)Z(\rightarrow c{\bar{c}})$$ ( W / Z ) Z ( → c c ¯ ) process and 3.8 (4.6) standard deviations for the $$(W/Z)W(\rightarrow cq)$$ ( W / Z ) W ( → c q ) process. The $$(W/Z)H(\rightarrow c {\bar{c}})$$ ( W / Z ) H ( → c c ¯ ) search yields an observed (expected) upper limit of 26 (31) times the predicted Standard Model cross-section times branching fraction for a Higgs boson with a mass of "Equation missing", corresponding to an observed (expected) constraint on the charm Yukawa coupling modifier $$|\kappa _c| < 8.5~(12.4)$$ | κ c | < 8.5 ( 12.4 ) , at the 95% confidence level. A combination with the ATLAS $$(W/Z)H, H\rightarrow b{\bar{b}}$$ ( W / Z ) H , H → b b ¯ analysis is performed, allowing the ratio $$\kappa _c / \kappa _b$$ κ c / κ b to be constrained to less than 4.5 at the 95% confidence level, smaller than the ratio of the b- and c-quark masses, and therefore determines the Higgs-charm coupling to be weaker than the Higgs-bottom coupling at the 95% confidence level.

A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 fb−1 of pp collision data at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 GeV and a Standard Model production cross section, an observed upper limit of 0.145 is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of 0.103. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 GeV to 2 TeV are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1.0 pb for a scalar boson mass of 50 GeV to 0.1 pb at a mass of 2 TeV.

Measurements of Higgs boson production cross-sections are carried out in the diphoton decay channel using 139 fb−1 of pp collision data at $$ \sqrt{s} $$ 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 $$ {1.04}_{-0.09}^{+0.10} $$ 1.04 − 0.09 + 0.10 . Cross-sections for gluon-gluon fusion, vector-boson 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 cross-sections 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.