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  1. Abstract The Phase-I trigger readout electronics upgrade of the ATLAS Liquid Argon calorimeters enhances thephysics reach of the experiment during the upcoming operation atincreasing Large Hadron Collider luminosities.The new system, installed during the second Large Hadron Collider Long Shutdown,increases the trigger readout granularity by up to a factor of tenas well as its precision and range.Consequently, the background rejection at trigger level is improvedthrough enhanced filtering algorithms utilizing the additional informationfor topological discrimination of electromagnetic and hadronic shower shapes.This paper presents the final designs of the new electronic elements,their custom electronic devices, the proceduresused to validate their proper functioning, andmore »the performance achievedduring the commissioning of this system.« less
    Free, publicly-accessible full text available May 1, 2023
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  4. A bstract Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass 125 GeV decays into four leptons ( ℓ = e , μ ). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons: H → XX/ZX → 4 ℓ , where the new boson X has a mass between 1 and 60 GeV. The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb − 1 at a centre-of-mass energy $$ \sqrt{s} $$ smore »= 13 TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay into XX/ZX , improving those from previous publications by a factor between two and four. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where X is interpreted to be a dark boson.« less
    Free, publicly-accessible full text available March 1, 2023
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  7. A bstract A search for the exotic decay of the Higgs boson ( H ) into a b $$ \overline{b} $$ b ¯ resonance plus missing transverse momentum is described. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb − 1 of pp collisions at $$ \sqrt{s} $$ s = 13 TeV. The search targets events from ZH production in an NMSSM scenario where H → $$ {\overset{\sim }{\chi}}_2^0{\overset{\sim }{\chi}}_1^0 $$ χ ~ 2 0 χ ~ 1 0 , with $$ {\overset{\sim }{\chi}}_2^0 $$ χ ~ 2 0 → $$ a{\overset{\sim }{\chi}}_1^0more »$$ a χ ~ 1 0 , where a is a light pseudoscalar Higgs boson and $$ {\overset{\sim }{\chi}}_{1,2}^0 $$ χ ~ 1 , 2 0 are the two lightest neutralinos. The decay of the a boson into a pair of b -quarks results in a peak in the dijet invariant mass distribution. The final-state signature consists of two leptons, two or more jets, at least one of which is identified as originating from a b -quark, and missing transverse momentum. Observations are consistent with Standard Model expectations and upper limits are set on the product of cross section times branching ratio for a three-dimensional scan of the masses of the $$ {\overset{\sim }{\chi}}_2^0 $$ χ ~ 2 0 , $$ {\overset{\sim }{\chi}}_1^0 $$ χ ~ 1 0 and a boson.« less
    Free, publicly-accessible full text available January 1, 2023
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  10. A bstract The fragmentation properties of jets containing b -hadrons are studied using charged B mesons in 139 fb − 1 of pp collisions at $$ \sqrt{s} $$ s = 13 TeV, recorded with the ATLAS detector at the LHC during the period from 2015 to 2018. The B mesons are reconstructed using the decay of B ± into J/ψK ± , with the J/ψ decaying into a pair of muons. Jets are reconstructed using the anti- k t algorithm with radius parameter R = 0 . 4. The measurement determines the longitudinal and transverse momentum profiles of the reconstructedmore »B hadrons with respect to the axes of the jets to which they are geometrically associated. These distributions are measured in intervals of the jet transverse momentum, ranging from 50 GeV to above 100 GeV. The results are corrected for detector effects and compared with several Monte Carlo predictions using different parton shower and hadronisation models. The results for the longitudinal and transverse profiles provide useful inputs to improve the description of heavy-flavour fragmentation in jets.« less
    Free, publicly-accessible full text available December 1, 2022