Search for long-lived, massive particles in events with a displaced vertex and a muon with large impact parameter in pp collisions at root s=13 TeV with the ATLAS detector

A search for long-lived particles decaying into hadrons and at least one muon is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced vertex. The analyzed dataset of proton-proton collisions at √ s = 13 TeV was collected with the ATLAS detector and corresponds to 136 fb − 1. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particle decays that occur in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are presented as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and interpreted as exclusion limits in scenarios with pair production of long-lived top squarks that decay via a small R -parity-violating coupling into a quark and a muon. Top squarks with masses up to 1.7 TeV are excluded for a lifetime of 0.1 ns, and masses below 1.3 TeV are excluded for lifetimes between 0.01 ns and 30 ns

Determination of jet calibration and energy resolution in proton–proton collisions at s = 8 TeV using the ATLAS detector

Abstract: The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150GeV<pT< 1500 GeV, and the relative energy resolution is (8.4±0.6)% for pT=100GeV and (23±2)% for pT=20GeV. The calibration scheme for jets with radius parameter R=1.0, for which jets receive a dedicated calibration of the jet mass, is also discussed

Measurement of jet-substructure observables in top quark, W boson and light jet production in proton-proton collisions at √s=13 TeV with the ATLAS detector

A measurement of jet substructure observables is presented using data collected in 2016 by the ATLAS experiment at the LHC with proton-proton collisions at s√ = 13 TeV. Large-radius jets groomed with the trimming and soft-drop algorithms are studied. Dedicated event selections are used to study jets produced by light quarks or gluons, and hadronically decaying top quarks and W bosons. The observables measured are sensitive to substructure, and therefore are typically used for tagging large-radius jets from boosted massive particles. These include the energy correlation functions and the N-subjettiness variables. The number of subjets and the Les Houches angularity are also considered. The distributions of the substructure variables, corrected for detector effects, are compared to the predictions of various Monte Carlo event generators. They are also compared between the large-radius jets originating from light quarks or gluons, and hadronically decaying top quarks and W bosons

Measurement of the CP-violating phase ϕ<inf>s</inf> in Bs0→J/ψϕ decays in ATLAS at 13 TeV

A measurement of the Bs0→J/ψϕ decay parameters using 80.5fb-1 of integrated luminosity collected with the ATLAS detector from 13 Te proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase ϕs, the width difference Δ Γ s between the Bs0 meson mass eigenstates and the average decay width Γ s. The values measured for the physical parameters are combined with those from 19.2fb-1 of 7 and 8 Te data, leading to the following: ϕs=-0.087±0.036(stat.)±0.021(syst.)radΔΓs=0.0657±0.0043(stat.)±0.0037(syst.)ps-1Γs=0.6703±0.0014(stat.)±0.0018(syst.)ps-1Results for ϕs and Δ Γ s are also presented as 68% confidence level contours in the ϕs–Δ Γ s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. ϕs and Δ Γ s measurements are in agreement with the Standard Model predictions

Measurement of jet-substructure observables in top quark, W boson and light jet production in proton-proton collisions at root s=13 TeV with the ATLAS detector

A measurement of jet substructure observables is presented using data collected in 2016 by the ATLAS experiment at the LHC with proton-proton collisions at root s= 13 TeV. Large-radius jets groomed with the trimming and soft-drop algorithms are studied. Dedicated event selections are used to study jets produced by light quarks or gluons, and hadronically decaying top quarks and W bosons. The observables measured are sensitive to substructure, and therefore are typically used for tagging large-radius jets from boosted massive particles. These include the energy correlation functions and the N-subjettiness variables. The number of subjets and the Les Houches angularity are also considered. The distributions of the substructure variables, corrected for detector effects, are compared to the predictions of various Monte Carlo event generators. They are also compared between the large-radius jets originating from light quarks or gluons, and hadronically decaying top quarks and W bosons

A search for the Z gamma decay mode of the Higgs boson in pp collisions at root s=13 TeV with the ATLAS detector

A search for the Z gamma decay of the Higgs boson, with Z boson decays into pairs of electrons or muons is presented. The analysis uses proton-proton collision data at root s = 13 TeV corresponding to an integrated luminosity of 139 fb(-1) recorded by the ATLAS detector at the Large Hadron Collider. The observed data are consistent with the expected background with a p-value of 1.3%. An upper limit at 95% confidence level on the production cross-section times the branching ratio for pp -> H -> Z gamma is set at 3.6 times the Standard Model prediction while 2.6 times is expected in the presence of the Standard Model Higgs boson. The best-fit value for the signal yield normalised to the Standard Model prediction is 2.0(-0.9)(+1.0) where the statistical component of the uncertainty is dominant. (C) 2020 The Author. Published by Elsevier B.V

Search for squarks and gluinos in final states with same-sign leptons and jets using 139 fb(-1) of data collected with the ATLAS detector

A search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge, or at least three isolated leptons. A data sample of proton-proton collisions at root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to a total integrated luminosity of 139 fb(-1), is used for the search. No significant excess over the Standard Model expectation is observed. The results are interpreted in simplified supersymmetric models featuring both R-parity conservation and R-parity violation, raising the exclusion limits beyond those of previous ATLAS searches to 1600 GeV for gluino masses and 750 GeV for bottom and top squark masses in these scenarios

Search for direct production of electroweakinos in final states with one lepton, missing transverse momentum and a Higgs boson decaying into two b-jets in pp collisions at \sqrt{s} = 12 TeV with the ATLAS detector

The results of a search for electroweakino pair production pp The results of a search for electroweakino pair production pp \rightarrow \check{\chi}\frac{+}{1}\check{\chi}\frac{0}{2} in which the chargino (\check{\chi}\frac{+}{1}) decays into a W boson and the lightest neutralino \check{\chi}\frac{0}{1} 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 fb^{-1} of \sqrt{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 \check{\chi}\frac{+}{1}\check{\chi}\frac{0}{2} up to 740 GeV are excluded at 95% confidence level for a massless \check{\chi}\frac{0}{1}