This article describes the design, construction and use of a calibration and monitoring system, based on movable 137Cs gamma-ray sources, for the ATLAS Tile Calorimeter (TileCal). The sources, propelled by a water-based liquid through tubes that traverse all the calorimeter's cells, produce signals that precisely characterise the response of each tile, thereby providing very granular and accurate data on the response of TileCal to particles. The system has been used to guide and control the quality of the optical instrumentation of all TileCal modules, to set and equalise the dynamic range of the response to physics data, and to set the energy scale of the readout system. In the ATLAS cavern, periodic measurements of the whole detector's response to 137Cs sources allow monitoring the uniformity and stability of all the calorimeter's cells as well as maintaining precise knowledge of its energy calibration. The design of the source hydraulic drive system's hardware and software, the data acquisition system and the data processing algorithms are described. Finally, the results of this two-decade program are shown.

Citation for published version (APA): Aaboud, M., Bentvelsen, S., Berge, D., Colijn, A. P., de Jong, P. J., Koffeman, E., Linde, F., Sabato, G., Salek, D., Stapf, B. S., Verkerke, W., Vermeulen, A. T., Vermeulen, J. C., Vreeswijk, M., van Vulpen, I., & al., E. (2019). Search for heavy charged long-lived particles in proton-proton collisions at = 13 TeV using an ionisation measurement with the ATLAS detector. Physics Letters B, 788, 96-116. https://doi.org/10.1016/j.physletb.2018.10.055

The production cross-sections for W +/- and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb-1 collected at a centre-ofmass energy v s = 2.76 TeV. The deca ...

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100TeV. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

Collaboration A measurement of off-shell Higgs boson production in the Z Z → 4 (cid:2) and Z Z → 2 (cid:2) 2 ν decay channels, where (cid:2) stands for either an electron or a muon, is performed using data from proton–proton collisions at a centre-of-mass energy of √ s = 13 TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36 . 1 fb − 1 . An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV. © 2018 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 .

A search for the decay of the Standard Model Higgs boson into a b ¯ b pair when produced in association with a W or Z boson is performed with the ATLAS detector. The data, corresponding to an integrated luminosity of 79 . 8 fb − 1 were collected in proton–proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.9 (4.3) standard deviations. A combination with the results from other searches in Run 1 and in Run 2 for the Higgs boson in the b ¯ b decay mode is performed, which yields an observed (expected) significance of 5.4 (5.5) standard deviations, thus providing direct observation of the Higgs boson decay into b -quarks. The ratio of the measured event yield for a Higgs boson decaying into b ¯ b to the Standard Model expectation is 1 . 01 ± 0 . 12 ( stat .) + 0 . 16 − 0 . 15 ( syst .) . Additionally, a combination of Run 2 results searching for the Higgs boson produced in association with a vector boson yields an observed (expected) significance of 5.3 (4.8) standard deviations.

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Collaboration A measurement of off-shell Higgs boson production in the Z Z → 4 (cid:2) and Z Z → 2 (cid:2) 2 ν decay channels, where (cid:2) stands for either an electron or a muon, is performed using data from proton–proton collisions at a centre-of-mass energy of √ s = 13 TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36 . 1 fb − 1 . An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV. © 2018 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 .

Measurements of dijet p T correlations in Pb + Pb and pp collisions at a nucleon–nucleon centre-of- mass energy of √ s NN = 2 . 76 TeV are presented. The measurements are performed with the ATLAS detector at the Large Hadron Collider using Pb + Pb and pp data samples corresponding to integrated luminosities of 0 . 14 nb − 1 and 4 . 0 pb − 1 , respectively. Jets are reconstructed using the anti- k t algorithm with radius parameter values R = 0 . 3 and R = 0 . 4. A background subtraction procedure is applied to correct the jets for the large underlying event present in Pb + Pb collisions. The leading and sub-leading jet transverse momenta are denoted p T 1 and p T 2 . An unfolding procedure is applied to the two-dimensional ( p T 1 , p T 2 ) distributions to account for experimental effects in the measurement of both jets. Distributions of ( 1 / N ) d N / d x J , where x J = p T 2 / p T 1 , are presented as a function of p T 1 and collision centrality. The distributions are found to be similar in peripheral Pb + Pb collisions and pp collisions, but highly modified in central Pb + Pb collisions. Similar features are present in both the R = 0 . 3 and R = 0 . 4 results, indicating that the effects of the underlying event are properly accounted for in the measurement. The results are qualitatively consistent with expectations from partonic energy loss models.

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to W W , W Z and Z Z final states in multiple decay channels using 20 . 3 fb − 1 of pp collision data at √ s = 8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to W Z in the (cid:3) ν (cid:3) (cid:3) (cid:3) (cid:3) ( (cid:3) = μ , e ), (cid:3)(cid:3) q ¯ q , (cid:3) ν q ¯ q and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the W Z bosons are compared with predictions of an extended gauge model with a heavy W (cid:3) boson. In addition, direct searches for a neutral diboson resonance decaying to W W and Z Z in the (cid:3)(cid:3) q ¯ q , (cid:3) ν q ¯ q , and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the W W and Z Z bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall–Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension. © 2016 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V. This is an open

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead–lead collisions at √ s NN = 2 . 76 TeV corresponding to an integrated luminosity of approximately 7 μb − 1 , ATLAS has measured jets with a calorimeter system over the pseudorapidity interval | η | < 2 . 1 and over the transverse momentum range 38 < p T < 210 GeV. Jets were reconstructed using the anti- k t algorithm with values for the distance parameter that determines the nominal jet radius of R = 0 . 2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet “central-to-peripheral ratio,” R CP . Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. R CP varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.

The Tile Calorimeter, covering the central region of the ATLAS experiment up to pseudorapidities of ±1.7, is a sampling device built with scintillating tiles that alternate with iron plates. The light is collected in wave-length shifting (WLS) fibers and is read out with photomultipliers. In the characteristic geometry of this calorimeter the tiles lie in planes perpendicular to the beams, resulting in a very simple and modular mechanical and optical layout. This paper focuses on the procedures applied in the optical instrumentation of the calorimeter, which involved the assembly of about 460,000 scintillator tiles and 550,000 WLS fibers. The outcome is a hadronic calorimeter that meets the ATLAS performance requirements, as shown in this paper.

This paper summarises the mechanical construction and installation of the Tile Calorimeter for the ATLAS experiment at the Large Hadron Collider in CERN, Switzerland. The Tile Calorimeter is a sampling calorimeter using scintillator as the sensitive detector and steel as the absorber and covers the central region of the ATLAS experiment up to pseudorapidities +/- 1.7. The mechanical construction of the Tile Calorimeter occurred over a period of about 10 years beginning in 1995 with the completion of the Technical Design Report and ending in 2006 with the installation of the final module in the ATLAS cavern. During this period approximately 2600 metric tons of steel were transformed into a laminated structure to form the absorber of the sampling calorimeter. Following instrumentation and testing, which is described elsewhere, the modules were installed in the ATLAS cavern with a remarkable accuracy for a structure of this size and weight.

Citation Aad, G., B. Abbott, J. Abdallah, S. Abdel Khalek, A.A. Abdelalim, O. Abdinov, B. Abi, et al. “Measurement of W and Z Production Cross Sections in Pp Collisions at s = 7 TeV and Limits on Anomalous Triple Gauge Couplings with the ATLAS Detector.” Physics Letters B 717, no. 1–3 (October 2012): 49–69. © 2012 CERN As Published http://dx.doi.org/10.1016/j.physletb.2012.09.017 Publisher Elsevier

The reconstruction of photons in the ATLAS detector is stud ied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS de tector was exposed to beams of particles of known energy at the CERN SPS. The results pres ent d show significant differences in the longitudinal development of the electromagnetic sho wer between converted and unconverted photons as well as in the total measured energy. The potentia l to use the reconstructed converted photons as a means to precisely map the material of the tracke r in front of the electromagnetic calorimeter is also considered. All results obtained are co mpared with a detailed Monte-Carlo simulation of the test-beam setup which is based on the same s imulation and reconstruction tools as those used for the ATLAS detector itself.

In 2004 at the ATLAS (A Toroidal LHC ApparatuS) combined test beam, one slice of the ATLAS barrel detector (including an Inner Detector set-up and the Liquid Argon calorimeter) was exposed to particles from the H8 SPS beam line at CERN. It was the first occasion to test the combined electron performance of ATLAS. This paper presents results obtained for the momentum measurement p with the Inner Detector and for the performance of the electron measurement with the LAr calorimeter (energy E linearity and resolution) in the presence of a magnetic field in the Inner Detector for momenta ranging from 20 GeV/c to 100 GeV/c. Furthermore the particle identification capabilities of the Transition Radiation Tracker, Bremsstrahlungs-recovery algorithms relying on the LAr calorimeter and results obtained for the E/p ratio and a way how to extract scale parameters will be discussed.

A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of the barrel calorimeter to hadrons with energies in the range 20–350GeV and beam impact points and angles corresponding to pseudo-rapidity values in the range 0.2–0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit.