9 research outputs found
Author Correction: A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery
No full textIn the version of this article initially published, the ATLAS Collaboration
author names, affiliations and acknowledgements were omitted and
have now been included in the HTML and PDF versions of the article
Emulating the impact of additional proton–proton interactions in the ATLAS simulation by presampling sets of inelastic Monte Carlo events
No full text© 2022, The Author(s).The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.FONDECYTMillennium Institute on Immunology and ImmunotherapyNucleus projec
Tuberculosis and COVID-19 co-infection: description of the global cohort
No full textBackground: Information on tuberculosis (TB) and coronavirus disease 2019 (COVID-19) is still limited. The aim of this study was to describe the features of the TB/COVID-19 co-infected individuals from a prospective, anonymised, multicountry register-based cohort with special focus on the determinants of mortality and other outcomes. Methods: We enrolled all patients of any age with either active TB or previous TB and COVID-19. 172 centres from 34 countries provided individual data on 767 TB-COVID-19 co-infected patients, (>50% population-based). Results: Of 767 patients, 553 (74.0%) out of 747 had TB before COVID-19 (including 234 out of 747 with previous TB), 71 (9.5%) out of 747 had COVID-19 first and 123 (16.5%) out of 747 had both diseases diagnosed within the same week (n=35 (4.6%) on the same day). 85 (11.08%) out of 767 patients died (41 (14.2%) out of 289 in Europe and 44 (9.2%) out of 478 outside Europe; p=0.03): 42 (49.4%) from COVID-19, 31 (36.5%) from COVID-19 and TB, one (1.2%) from TB and 11 from other causes. In the univariate analysis on mortality the following variables reached statistical significance: age, male gender, having more than one comorbidity, diabetes mellitus, cardiovascular disease, chronic respiratory disease, chronic renal disease, presence of key symptoms, invasive ventilation and hospitalisation due to COVID-19. The final multivariable logistic regression model included age, male gender and invasive ventilation as independent contributors to mortality. Conclusion: The data suggest that TB and COVID-19 are a "cursed duet" and need immediate attention. TB should be considered a risk factor for severe COVID disease and patients with TB should be prioritised for COVID-19 preventative efforts, including vaccination.
(The TB/COVID-19 Global Study Group
AtlFast3: The Next Generation of Fast Simulation in ATLAS
No full textThe ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes
Searches for new phenomena in events with two leptons, jets, and missing transverse momentum in 139 fb - 1 of √s=13 TeV pp collisions with the ATLAS detector
No full textSearches for new phenomena inspired by supersymmetry in final states containing an e+e− or μ+μ− pair, jets, and missing transverse momentum are presented. These searches make use of proton–proton collision data with an integrated luminosity of 139 fb−1, collected during 2015–
2018 at a centre-of-mass energy √s = 13 TeV by the ATLAS detector at the Large Hadron Collider. Two searches target the pair production of charginos and neutralinos. One uses the recursive-jigsaw reconstruction technique to follow up on excesses observed in 36.1 fb−1 of data, and the other uses conventional event variables. The third search targets pair production of coloured supersymmetric particles (squarks or gluinos) decaying through the next-to-lightest neutralino
(χ ̃ 02 ) via a slepton ( ) ̃ or Z boson into + −χ ̃ 01 , resulting in a kinematic endpoint or peak in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectations. Results are interpreted using simplified models and exclude masses up to 900 GeV for electroweakinos, 1550 GeV for squarks, and 2250 GeV for gluinos
Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector
No full textThis paper presents a measurement of b-jet production in Pb+Pb and pp collisions at TeV with the ATLAS detector at the LHC. The measurement uses 260 of pp collisions collected in 2017 and 1.4 of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti- algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters and , and only jets are used in Pb+Pb collisions. For comparison, inclusive jets are also measured using 1.7 of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, , is calculated for both b-jets and inclusive jets with over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet to inclusive jet is also presented and suggests that the for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions
Measurements of observables sensitive to colour reconnection in t(t)over-bar events with the ATLAS detector at √s=13TeV
No full textA measurement of observables sensitive to effects
of colour reconnection in top-quark pair-production events
is presented using 139 fb−1 of 13 TeV proton–proton collision data collected by the ATLAS detector at the LHC.
Events are selected by requiring exactly one isolated electron and one isolated muon with opposite charge and two
or three jets, where exactly two jets are required to be btagged. For the selected events, measurements are presented
for the charged-particle multiplicity, the scalar sum of the
transverse momenta of the charged particles, and the same
scalar sum in bins of charged-particle multiplicity. These
observables are unfolded to the stable-particle level, thereby
correcting for migration effects due to finite detector resolution, acceptance and efficiency effects. The particle-level
measurements are compared with different colour reconnection models in Monte Carlo generators. These measurements
disfavour some of the colour reconnection models and provide inputs to future optimisation of the parameters in Monte
Carlo generators
Constraints on spin-0 dark matter mediators and invisible Higgs decays using ATLAS 13 TeV pp collision data with two top quarks and missing transverse momentum in the final state
No full textThis paper presents a statistical combination of
searches targeting final states with two top quarks and invisible particles, characterised by the presence of zero, one or
two leptons, at least one jet originating from a b-quark and
missing transverse momentum. The analyses are searches for
phenomena beyond the Standard Model consistent with the
direct production of dark matter in pp collisions at the LHC,
using 139 fb−1 of data collected with the ATLAS detector at a centre-of-mass energy of 13 TeV. The results are
interpreted in terms of simplified dark matter models with
a spin-0 scalar or pseudoscalar mediator particle. In addition, the results are interpreted in terms of upper limits on
the Higgs boson invisible branching ratio, where the Higgs
boson is produced according to the Standard Model in association with a pair of top quarks. For scalar (pseudoscalar) dark
matter models, with all couplings set to unity, the statistical
combination extends the mass range excluded by the best of
the individual channels by 50 (25) GeV, excluding mediator
masses up to 370 GeV. In addition, the statistical combination improves the expected coupling exclusion reach by 14%
(24%), assuming a scalar (pseudoscalar) mediator mass of
10 GeV. An upper limit on the Higgs boson invisible branching ratio of 0.38 (0.30+0.13
−0.09) is observed (expected) at 95%
confidence level
Search for Higgs boson pair production in association with a vector boson in pp collisions at √s=13TeV with the ATLAS detector
No full textThis paper reports a search for Higgs boson
pair (hh) production in association with a vector boson
(W or Z) using 139 fb−1 of proton–proton collision data
at √s = 13 TeV recorded with the ATLAS detector at the
Large Hadron Collider. The search is performed in final
states in which the vector boson decays leptonically (W →
ν, Z → , νν with = e, μ) and the Higgs bosons each
decay into a pair of b-quarks. It targets Vhh signals from
both non-resonant hh production, present in the Standard
Model (SM), and resonant hh production, as predicted in
some SM extensions. A 95% confidence-level upper limit of
183 (87) times the SM cross-section is observed (expected)
for non-resonant V hh production when assuming the kinematics are as expected in the SM. Constraints are also placed
on Higgs boson coupling modifiers. For the resonant search,
upper limits on the production cross-sections are derived for
two specific models: one is the production of a vector boson
along with a neutral heavy scalar resonance H, in the mass
range 260–1000 GeV, that decays into hh, and the other is
the production of a heavier neutral pseudoscalar resonance
A that decays into a Z boson and H boson, where the A
boson mass is 360–800 GeV and the H boson mass is 260–
400 GeV. Constraints are also derived in the parameter space
of two-Higgs-doublet models
