The results of a search for electroweakino pair production $$pp \rightarrow \tilde{\chi }^\pm _1 \tilde{\chi }^0_2$$pp→χ~1±χ~20 in which the chargino ( $$\tilde{\chi }^\pm _1$$χ~1± ) decays into a W boson and the lightest neutralino ( $$\tilde{\chi }^0_1$$χ~10 ), while the heavier neutralino ( $$\tilde{\chi }^0_2$$χ~20 ) decays into the Standard Model 125 GeV Higgs boson and a second $$\tilde{\chi }^0_1$$χ~10 are presented. The signal selection requires a pair of b-tagged jets consistent with those from a Higgs boson decay, and either an electron or a muon from the W boson decay, together with missing transverse momentum from the corresponding neutrino and the stable neutralinos. The analysis is based on data corresponding to 139 $$\mathrm {fb}^{-1}$$fb-1 of $$\sqrt{s}=13$$s=13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically significant evidence of an excess of events above the Standard Model expectation is found. Limits are set on the direct production of the electroweakinos in simplified models, assuming pure wino cross-sections. Masses of $$\tilde{\chi }^{\pm }_{1}/\tilde{\chi }^{0}_{2}$$χ~1±/χ~20 up to 740 GeV are excluded at 95% confidence level for a massless $$\tilde{\chi }^{0}_{1}$$χ~10 .

A measurement of observables sensitive to spin correlations in $$t\bar{t}$$tt¯ production is presented, using 36.1 $$\hbox {fb}^{-1}$$fb-1 of pp collision data at $$\sqrt{s} = 13$$s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the $$t\bar{t}$$tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.

Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools/reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. The content and structure of this report are guided by the scope and priorities defined in the mandate of the FCC Feasibility Study. It is therefore not intended to serve as an exhaustive review of the full physics potential of FCC. Several topics, already covered in earlier reports such as the FCC CDR, are not reiterated here or are addressed only briefly, in alignment with the study’s focus. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

A measurement of the $$ B_{s}^{0} \rightarrow J/\psi \phi $$B s 0 → J / ψ ϕ decay parameters using $$ 80.5\, \mathrm {fb^{-1}} $$80.5 fb - 1 of integrated luminosity collected with the ATLAS detector from 13 $$\text {Te}\text {V}$$Te proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase $$\phi _{s} $$ϕ s , the width difference $$ \Delta \Gamma _{s}$$Δ Γ s between the $$B_{s}^{0}$$B s 0 meson mass eigenstates and the average decay width $$ \Gamma _{s}$$Γ s . The values measured for the physical parameters are combined with those from $$ 19.2\, \mathrm {fb^{-1}} $$19.2 fb - 1 of 7 and 8 $$\text {Te}\text {V}$$Te data, leading to the following: $$\begin{aligned} \phi _{s}= & {} -0.087 \pm 0.036 ~\mathrm {(stat.)} \pm 0.021 ~\mathrm {(syst.)~rad} \\ \Delta \Gamma _{s}= & {} 0.0657 \pm 0.0043 ~\mathrm {(stat.)}\pm 0.0037 ~\mathrm {(syst.)~ps}^{-1} \\ \Gamma _{s}= & {} 0.6703 \pm 0.0014 ~\mathrm {(stat.)}\pm 0.0018 ~\mathrm {(syst.)~ps}^{-1} \end{aligned}$$ϕ s = - 0.087 ± 0.036 ( stat . ) ± 0.021 ( syst . ) rad Δ Γ s = 0.0657 ± 0.0043 ( stat . ) ± 0.0037 ( syst . ) ps - 1 Γ s = 0.6703 ± 0.0014 ( stat . ) ± 0.0018 ( syst . ) ps - 1 Results for $$\phi _{s} $$ϕ s and $$ \Delta \Gamma _{s}$$Δ Γ s are also presented as 68% confidence level contours in the $$\phi _{s} $$ϕ s – $$ \Delta \Gamma _{s}$$Δ Γ s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. $$\phi _{s} $$ϕ s and $$ \Delta \Gamma _{s}$$Δ Γ s measurements are in agreement with the Standard Model predictions.

The production cross-section of a top quark in association with aWboson is measured using proton–proton collisions at $$\sqrt{s} = 8\,\text {TeV}$$s=8TeV . The dataset corresponds to an integrated luminosity of $$20.2\,\text {fb}^{-1}$$20.2fb-1 , and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate thetWsignal from the dominant $$t{\bar{t}}$$tt¯ background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decayingWboson. The measured cross-section is $$\sigma _{tW} = 26 \pm 7\,\text {pb}$$σtW=26±7pb , in good agreement with the Standard Model expectation.

In addition to high-energy hadrons, which include neutrons, protons and pions above 20 MeV, thermal neutrons are a major concern in terms of Soft Error Rate (SER) for electronics operating in the Large Hadron Collider (LHC) accelerator at CERN. Most of the electronic devices still contain Boron-10 inside their structure, which makes them sensitive to thermal neutrons. The LHC radiation environment in different tunnel and shielded areas is analyzed through measurements and FLUKA simulations, showing that the thermal neutron fluence can be considerably higher than the high energy one, up to a factor of 50. State-of-the-art Commercial Off The Shelf (COTS) components such as SRAM, FPGA and Flash memories of different technologies are studied to derive the expected Single Event Upset (SEU) rate due to thermal neutrons, relative to the high-energy hadron contribution. We find that, for the studied parts and most of the accelerator applications, thermal neutrons are the dominating source of upsets with respect to the high energy particles yielding even to neglect the latter in some cases. Indeed, they can induce in electronics up to more than 90% of the total upsets. The estimation is performed also for ground level and avionic applications, and although in general thermal neutrons are not the main source of SER, in Flash memories they can play the same role as high energy neutrons. Related Radiation Hardness Assurance (RHA) considerations for the qualification of components and systems against thermal neutrons are presented.