The production of a prompt photon in association with a Z boson is studied in proton-proton collisions at a centre-of-mass energy √ s = 13 TeV. The analysis uses a data sample with an integrated luminosity of 139 fb −1 collected by the ATLAS detector at the LHC from 2015 to 2018. The production cross-section for the process pp → + − γ + X (= e, µ) is measured within a fiducial phase-space region defined by kinematic requirements on the photon and the leptons, and by isolation requirements on the photon. An experimental precision of 2.9% is achieved for the fiducial cross-section. Differential crosssections are measured as a function of each of six kinematic variables characterising the + − γ system. The data are compared with theoretical predictions based on next-toleading-order and next-to-next-to-leading-order perturbative QCD calculations. The impact of next-to-leading-order electroweak corrections is also considered.

Measurement of V H, H → bb production as a function of the vector-boson transverse momentum in 13 TeV p p collisions with the ATLAS detectorThe ATLAS Collaboration Cross-sections of associated production of a Higgs boson decaying into bottom-quark pairs and an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the 'simplified template cross-section' framework. The results are obtained using 79.8 fb −1 of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons.A particle consistent with the Standard Model (SM) predictions for the Higgs boson [1][2][3][4] was observed in 2012 by the ATLAS and CMS collaborations [5, 6] at the LHC. Further analysis of ATLAS and CMS data collected in proton-proton (pp) collisions at centre-of-mass energies of 7 TeV, 8 TeV and 13 TeV in two LHC data-taking periods (Runs 1 and 2) has led to precise measurements of the mass of this particle (around 125 GeV) [7-9], tests of its spin and parity (J P = 0 + ) against alternative hypotheses [10, 11], as well as to measurements of its production and decay rates [12][13][14].Recently, experiments at the LHC observed Higgs boson production in association with weak gauge bosons V = W, Z (V H production) [15] and Higgs boson decays into pairs of bottom quarks (H → bb) [15, 16]. With these results, the four most important Higgs boson production modes predicted by the SM, gluon-gluon fusion (ggF), vector-boson fusion (VBF), and associated production of a Higgs boson with either a weak gauge boson (V H) or a top-quark pair (ttH) are established. Similarly, several of the main modes of Higgs boson decays into fermionic (bb, ττ) and bosonic (WW, Z Z, γγ) final states are observed. All results, typically expressed in the form of 'signal strengths', defined as the ratio of the observed to the expected product of the production cross-section times branching ratio into a certain final state, are consistent with SM predictions within uncertainties.To probe the kinematic properties of Higgs boson production in more detail, to reduce the impact of theoretical uncertainties on the measurements and to make the measurements easier to compare with future updated calculations, the framework of simplified template cross-sections (STXS) has been introduced [17, 18]. In this framework, the cross-sections for the various Higgs boson production modes are measured in exclusive regions carefully defined by fiducial selections based on the kinematic properties of Higgs boson production. The extrapolation from the phase space selected by the analysis criteria to that for which the cross-section measurements are presented is thus red...

silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-250) [2, 3] and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.

Measurement of the inclusive isolated-photon cross section in pp collisions at √ s = 13 TeV using 36 fb −1 of ATLAS dataThe ATLAS CollaborationThe differential cross section for isolated-photon production in pp collisions is measured at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC using an integrated luminosity of 36.1 fb −1 . The differential cross section is presented as a function of the photon transverse energy in different regions of photon pseudorapidity. The differential cross section as a function of the absolute value of the photon pseudorapidity is also presented in different regions of photon transverse energy. Next-to-leading-order QCD calculations from Jetphox and Sherpa as well as next-to-next-to-leading-order QCD calculations from Nnlojet are compared with the measurement, using several parameterisations of the proton parton distribution functions. The predictions provide a good description of the data within the experimental and theoretical uncertainties. c 2019 CERN for the benefit of the ATLAS Collaboration. Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 license. γ T > 125 GeV and |η γ | < 2.37, excluding the region 1.37 < |η γ | < 1.56. In addition, the double-differential cross section as a function of |η γ | in different regions of E γ T is also presented. The results are based on a data sample with a more than ten-fold increase in statistics relative to the previous study [5]. The measurement presented here is found to be consistent with the previous one in the overlapping kinematic regions. This increase in statistics allows improvements in the calibration of the photon energy and reductions in the experimental systematic uncertainties affecting the cross-section measurement, as well as an extension of the coverage in E γ T to higher values than previously measured. In this analysis, the region where the measurement is limited by systematic uncertainties is extended to E γ T ∼ 1 TeV, beyond what was achieved in the previous measurement. The NLO QCD predictions of Jetphox [19,20] and Sherpa [21] based on several parameterisations of the PDFs are compared with the measurement. The NNLO QCD prediction of Nnlojet [16], which has significantly reduced uncertainties due to fewer missing higher-order terms, is also confronted with the data. ATLAS detectorThe ATLAS detector [22][23][24] is a multipurpose detector with a forward-backward symmetric cylindrical geometry. 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 toroid magnets. The inner-detector system 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 is closest to the interaction region and provides four measurements per track. The pixel detector is followed by the silicon microstrip tracker, which typically provides four three-dimension...

This paper presents a measurement of ZZ production with the ATLAS detector at the Large Hadron Collider. The measurement is carried out in the final state with two charged leptons and two neutrinos, using data collected during 2015 and 2016 in pp collisions at √ s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb −1. The integrated cross-sections in the total and fiducial phase spaces are measured with an uncertainty of 7% and compared with Standard Model predictions, and differential measurements in the fiducial phase space are reported. No significant deviations from the Standard Model predictions are observed, and stringent constraints are placed on anomalous couplings corresponding to neutral triple gauge-boson interactions.