Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at √ s = 7 and 8 TeV The ATLAS and CMS collaborations Abstract: Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H → ZZ, W W , γγ, τ τ, bb, and µµ. All results are reported assuming a value of 125.09 GeV for the Higgs boson mass, the result of the combined measurement by the ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb −1 at √ s = 7 TeV and 20 fb −1 at √ s = 8 TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 ± 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H → τ τ decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered. Production Event generator process ATLAS CMS ggF Powheg [80-84] Powheg VBF Powheg Powheg W H Pythia8 [85] Pythia6.4 [86] ZH (qq → ZH or qg → ZH) Pythia8 Pythia6.4 ggZH (gg → ZH) Powheg See text ttH Powhel [88] Pythia6.4 where all κ j values equal unity in the SM; here, by construction, the SM cross sections and branching fractions include the best available higher-order QCD and EW corrections. This higher-order accuracy is not necessarily preserved for κ j values different from unity, but the dominant higher-order QCD corrections factorise to a large extent from any rescaling of the coupling strengths and are therefore assumed to remain valid over the entire range of κ j values considered in this paper. Different production processes and decay modes probe different coupling modifiers, as can be visualised from the Feynman diagrams shown in figures 1-6. Individual coupling modifiers, corresponding to tree-level Higgs boson couplings to the different particles, are introduced, as well as two effective coupling modifiers, κ g and κ γ , which describe the loop processes for ggF production and H → γγ decay. This is possible because BSM particles that might be present in these loops are not expected to appreciably change the kinematics of the corresponding process. The gg → H and H → γγ loop p...

This article documents the performance of the ATLAS muon identification and reconstruction using the LHC dataset recorded at  TeV in 2015. Using a large sample of and decays from 3.2 fb of pp collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to over most of the covered phase space ( and  GeV). The isolation efficiency varies between 93 and depending on the selection applied and on the momentum of the muon. Both efficiencies are well reproduced in simulation. In the central region of the detector, the momentum resolution is measured to be () for muons from () decays, and the momentum scale is known with an uncertainty of . In the region , the resolution for muons from decays is while the precision of the momentum scale for low- muons from decays is about .

Studies of the spin, parity and tensor couplings of the Higgs boson in the , and decay processes at the LHC are presented. The investigations are based on of pp collision data collected by the ATLAS experiment at  TeV and  TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers , is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the and decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.

ATLAS has measured two-particle correlations as a function of the relative azimuthal angle, Δϕ, and pseudorapidity, Δη, in ffiffi ffi s p ¼ 13 and 2.76 TeV pp collisions at the LHC using charged particles measured in the pseudorapidity interval jηj < 2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at Δϕ ∼ 0 that extends over a wide range of Δη, which has been referred to as the "ridge." Per-trigger-particle yields, YðΔϕÞ, are measured over 2 < jΔηj < 5. For both collision energies, the YðΔϕÞ distribution in all multiplicity intervals is found to be consistent with a linear combination of the per-trigger-particle yields measured in collisions with less than 20 reconstructed tracks, and a constant combinatoric contribution modulated by cos ð2ΔϕÞ. The fitted Fourier coefficient, v 2;2 , exhibits factorization, suggesting that the ridge results from per-event cos ð2ϕÞ modulation of the single-particle distribution with Fourier coefficients v 2 . The v 2 values are presented as a function of multiplicity and transverse momentum. They are found to be approximately constant as a function of multiplicity and to have a p T dependence similar to that measured in p þ Pb and Pb þ Pb collisions. The v 2 values in the 13 and 2.76 TeV data are consistent within uncertainties. These results suggest that the ridge in pp collisions arises from the same or similar underlying physics as observed in p þ Pb collisions, and that the dynamics responsible for the ridge has no strong ffiffi ffi s p dependence. DOI: 10.1103/PhysRevLett.116.172301 Measurements of two-particle angular correlations in high-multiplicity proton-proton (pp) collisions at a centerof-mass energy ffiffi ffi s p ¼ 7 TeV at the LHC showed an enhancement in the production of pairs at small azimuthal-angle separation, Δϕ, that extends over a wide range of pseudorapidity differences, Δη, and which is often referred to as the "ridge" [1]. The ridge has also been observed in proton-lead (p þ Pb) collisions [2][3][4][5][6][7], where it is found to result from a global sinusoidal modulation of the per-event single-particle azimuthal angle distributions [3][4][5][6] TeV data recorded during LHC run 2 and run 1, respectively, to address these issues. The maximum number of inelastic interactions per crossing was 0.04 and 0.5 for the 13 and 2.76 TeV data, respectively. Two-particle angular correlations are measured as a function of Δη and Δϕ in different intervals of the measured charged-particle multiplicity and different p T intervals spanning 0.3 < p T < 5 GeV: 0.3-0.5 GeV, 0.5-1 GeV, 1-2 GeV, 2-3 GeV, 3-5 GeV. Separate p T -integrated results use 0.5 < p T < 5 GeV. Per-trigger-particle yields are obtained from the long-range (jΔηj > 2) component of the correlation. A new template-fitting method is applied to these yields to test for sinusoidal modulation similar to that observed in p þ Pb collisions. The measurements were performed using the ATLAS inner detector (ID), min...

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