Browsing by Author "Leeuw, Lerothodi"

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    Improved reconstruction of highly boosted -lepton pairs in the decay channels with the ATLAS detector
    (Springer Nature, 2025) Leeuw, Lerothodi; Zwalinski, Lukasz; Zormpa, Olga
    This paper presents a new -lepton reconstruction and identification procedure at the ATLAS detector at the Large Hadron Collider, which leads to significantly improved performance in the case of physics processes where a highly boosted pair of -leptons is produced and one -lepton decays into a muon and two neutrinos , and the other decays into hadrons and one neutrino. By removing the muon information from the signals used for reconstruction and identification of the candidate in the boosted pair, the efficiency is raised to the level expected for an isolated. The new procedure is validated by selecting a sample of highly boosted candidates from the data sample of 140 of proton–proton collisions at 13 TeV recorded with the ATLAS detector. Good agreement is found between data and simulation predictions in both the signal region and in a background validation region. The results presented in this paper demonstrate the effectiveness of the reconstruction with muon removal in enhancing the signal sensitivity of the boosted channel at the ATLAS detector.
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    The interstellar medium scaling relations in cosmological simulations
    (University of the Western Cape, 2022) Sibiya, Mpendulo; Leeuw, Lerothodi
    This work presents the scaling relations for the redshift zero galaxies in the SIMBA1 cosmological hydrodynamic simulations. The aim is to test the degree to which the SIMBA simulations reproduce the physical properties observed in real galaxies, as this simulation has advanced dust models that will better our understanding of hydrodynamic simulation’s sub-grid models, galaxy formation, and galaxy evolution. To achieve this, we studied and compared the scaling relations of observed galaxies from the DustPedia2 observational database and the scaling relations of the SIMBA simulated galaxies. We selected galaxies ranging from a minimum stellar mass of 109M⊙ and a minimum specific star-formation of 1010.5/yr to the upper limit of the galaxies in the snapshot. These selection criteria are used to make sure that our sample contains galaxies with an active interstellar medium3(ISM).
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    Search for Higgs boson decays into a pair of pseudoscalar particles in the γγτhadτhad final state using pp collisions at s = 13 TeV with the ATLAS detector
    (Springer Science and Business Media Deutschland GmbH, 2025) Leeuw, Lerothodi; Aad, Georges; Aakvaag, Erlend
    A search for exotic decays of the 125 GeV Higgs boson into a pair of new spin-0 particles, H → aa, where one decays into a photon pair and the other into a τ-lepton pair, is presented. Hadronic decays of the τ-leptons are considered and reconstructed using a dedicated tagger for collimated τ-lepton pairs. The search uses 140 fb−1 of proton-proton collision data at a centre-of-mass energy of s = 13 TeV recorded between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider. The search is performed in the mass range of the a boson between 10 GeV and 60 GeV. No significant excess of events is observed above the Standard Model background expectation. Model-independent upper limits at 95% confidence level are set on the branching ratio of the Higgs boson to the γγττ final state, B(H → aa → γγττ), ranging from 0.2% to 2%, depending on the a-boson mass hypothesis.
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    Test of lepton flavour universality in W-boson decays into electrons and τ-leptons using pp collisions at = 13 TeV with the ATLAS detector
    (Springer Science and Business Media Deutschland GmbH, 2025) Leeuw, Lerothodi; Aad, Georges; Aakvaag, Erlend
    A measurement of the ratio of the branching fractions, Rτ/e = B(W → τν)/B(W → eν), is performed using a sample of W bosons originating from top-quark decays to final states containing τ-leptons or electrons. This measurement uses pp collisions at = 13 TeV, collected by the ATLAS experiment at the Large Hadron Collider during Run 2, corresponding to an integrated luminosity of 140 fb−1. The W → τντ (with τ → eνeντ) and W → eνe decays are distinguished using the differences in the impact parameter distributions and transverse momentum spectra of the electrons. The measured ratio of branching fractions Rτ/e = 0.975 ± 0.012 (stat.) ± 0.020 (syst.), is consistent with the Standard Model assumption of lepton flavour universality in W-boson decays.