ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bouchhar, N., Cabrera Urban, S., et al. (2024). Fiducial and differential cross-section measurements of electroweak Wγjj production in pp collisions at √s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 84(10), 1064–34pp.
Abstract: The observation of the electroweak production of a W boson and a photon in association with two jets, using pp collision data at the Large Hadron Collider at a centre of mass energy of root s =13 TeV, is reported. The data were recorded by the ATLAS experiment from 2015 to 2018 and correspond to an integrated luminosity of 140 fb(-1). This process is sensitive to the quartic gauge boson couplings via the vector boson scattering mechanism and provides a stringent test of the electroweak sector of the Standard Model. Events are selected if they contain one electron or muon, missing transverse momentum, at least one photon, and two jets. Multivariate techniques are used to distinguish the electroweak W gamma jj process from irreducible background processes. The observed significance of the electroweak W gamma jj process is well above six standard deviations, compared to an expected significance of 6.3 standard deviations. Fiducial and differential cross sections are measured in a fiducial phase space close to the detector acceptance, which are in reasonable agreement with leading order Standard Model predictions from MadGraph5+Pythia8 and Sherpa. The results are used to constrain new physics effects in the context of an effective field theory.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Search for a light charged Higgs boson in t → H±b decays, with H± → cs, in pp collisions at √s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 85(2), 153–34pp.
Abstract: A search for a light charged Higgs boson produced in decays of the top quark, t -> H(+/-)b with H-+/- -> cs, is presented. This search targets the production of top-quark pairs t (t) over bar. WbH(+/-)b, with W -> lv (l = e, mu), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant t (t) over bar background. The data analysed correspond to 140 fb(-1) of pp collisions at root s = 13 TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction B(t -> H(+/-)b), assuming B(t -> Wb) + B(t -> H +/-(-> cs)b) = 1.0, are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV.
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Lima, F. C. E., Casana, R., & Almeida, C. A. S. (2024). Kinks and double-kinks in generalized φ4-and φ8-models. Eur. Phys. J. C, 84(12), 1266–12pp.
Abstract: Examining the phi 4 and phi 8 models within a two-dimensional framework in the flat spacetime and embracing a theory with unconventional kinetic terms, one investigates the emergence of kinks/antikinks and double-kinks/antikinks. We devote our study to obtaining the field configurations with minimal energy, i.e., solutions possessing a Bogomol'nyi-Prasad-Sommerfield's bound. Next, to accomplish our goal, we adopt non-polynomial generalizing functions, namely, hyperbolic sine and cosine functions: the first produce BPS potentials exhibiting a minimum at phi=0, facilitating the emergence of genuine double-kink-type configurations. Conversely, the second promotes the rise of kink-type solutions.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Operation and performance of the ATLAS tile calorimeter in LHC Run 2. Eur. Phys. J. C, 84(12), 1313–53pp.
Abstract: The ATLAS tile calorimeter (TileCal) is the hadronic sampling calorimeter covering the central region of the ATLAS detector at the Large Hadron Collider (LHC). This paper gives an overview of the calorimeter's operation and performance during the years 2015-2018 (Run 2). In this period, ATLAS collected proton-proton collision data at a centre-of-mass energy of 13 TeV and the TileCal was 99.65% efficient for data-taking. The signal reconstruction, the calibration procedures, and the detector operational status are presented. The performance of two ATLAS trigger systems making use of TileCal information, the minimum-bias trigger scintillators and the tile muon trigger, is discussed. Studies of radiation effects allow the degradation of the output signals at the end of the LHC and HL-LHC operations to be estimated. Finally, the TileCal response to isolated muons, hadrons and jets from proton-proton collisions is presented. The energy and time calibration methods performed excellently, resulting in good stability and uniformity of the calorimeter response during Run 2. The setting of the energy scale was performed with an uncertainty of 2%. The results demonstrate that the performance is in accordance with specifications defined in the Technical Design Report.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2024). Underlying-event studies with strange hadrons in pp collisions at √s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 84(12), 1335–29pp.
Abstract: Properties of the underlying-event in pp interactions are investigated primarily via the strange hadrons K-S(0), Lambda and (Lambda) over bar, as reconstructed using the ATLAS detector at the LHC in minimum-bias pp collision data at root s = 13 TeV. The hadrons are reconstructed via the identification of the displaced two-particle vertices corresponding to the decay modes K-S(0) -> pi(+)pi(-), Lambda -> pi(-) p and (Lambda) over bar -> pi(+) (p) over bar. These are used in the construction of underlying-event observables in azimuthal regions computed relative to the leading charged-particle jet in the event. None of the hadronisation and underlying-event physics models considered can describe the data over the full kinematic range considered. Events with a leading charged-particle jet in the range of 10 < p(T) <= 40 GeV are studied using the number of prompt charged particles in the transverse region. The ratio N(Lambda + <(Lambda)over bar>)/N(K-S(0)) as a function of the number of such charged particles varies only slightly over this range. This disagrees with the expectations of some of the considered Monte Carlo models.
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