CORE
COnnecting
REpositories

    40 research outputs found

    Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    A measurement of the charge asymmetry in top-quark pair (tt¯) production in association with a photon is presented. The measurement is performed in the single-lepton tt¯ decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb−1. The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be AC=−0.003±0.029 in agreement with the Standard Model expectation
    University of Liverpool Repository
    Archivio della ricerca - Università degli studi di Napoli "Parthenope"
    Pontificia Universidad Católica de Chile: Repositorio UC
    Crossref
    Archivio Istituzionale della Ricerca - Università degli Studi di Pavia
    Directory of Open Access Journals
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    Enlighten
    Queen Mary Research Online
    ART

    Exploration at the high-energy frontier: ATLAS Run 2 searches investigating the exotic jungle beyond the Standard Model

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    This report presents a comprehensive collection of searches for new physics performed by the ATLAS Collaboration during the Run 2 period of data taking at the Large Hadron Collider, from 2015 to 2018, corresponding to about 140 fb−1 of s = 13 TeV proton–proton collision data. These searches cover a variety of beyond-the-standard model topics such as dark matter candidates, new vector bosons, hidden-sector particles, leptoquarks, or vector-like quarks, among others. Searches for supersymmetric particles or extended Higgs sectors are explicitly excluded as these are the subject of separate reports by the Collaboration. For each topic, the most relevant searches are described, focusing on their importance and sensitivity and, when appropriate, highlighting the experimental techniques employed. In addition to the description of each analysis, complementary searches are compared, and the overall sensitivity of the ATLAS experiment to each type of new physics is discussed. plots and statistical combinations of multiple searches are included whenever possible
    University of Liverpool Repository
    HAL Université de Toulouse, et Toulouse INP
    AIR Universita degli studi di Milano
    eScholarship - University of California
    Portail HAL-PSL

    TeV with the ATLAS detector

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a Zγ pair in association with two jets. The analysis uses 140 fb−1 of LHC proton–proton collision data taken at √s = 13 TeV recorded by the ATLAS detector during the years 2015–2018. Events with a Z boson candidate decaying into either an e+e− or μ+μ− pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and by using the information about the centrality of the system and is measured with an observed and expected significance well above five standard deviations. The fiducial pp → Zγ jj cross-section for the electroweak production is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be 16.8+2.0 −1.8 fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    The University of Arizona
    Enlighten
    Queen Mary Research Online
    ART
    Archives ouvertes de Paris-Saclay
    Crossref
    AIR Universita degli studi di Milano
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    USURJ: University of Saskatchewan Undergraduate Research Journal
    Open Access Repository

    Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    This Letter reports on a search for off-shell production of the Higgs boson using 139 fb−1 of pp collision data at √s = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The signature is a pair of Z bosons, with contributions from both the production and subsequent decay of a virtual Higgs boson and the interference of that process with other processes. The two observable final states are Z Z → 4 and Z Z → 22ν with = e or μ. In the Z Z → 4 final state, a dense Neural Network is used to enhance analysis sensitivity with respect to matrix element-based discrimination. The backgroundonly hypothesis is rejected with an observed (expected) significance of 3.3 (2.2) standard deviations, representing experimental evidence for off-shell Higgs boson production. Assuming that no new particles enter the production of the virtual Higgs boson, its total width can be deduced from the measurement of its off-shell production cross-section. The measured total width of the Higgs boson is 4.5+3.3 −2.5 MeV, and the observed (expected) upper limit on the total width is found to be 10.5 (10.9) MeV at 95% confidence level
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Crossref
    Archivio Istituzionale della Ricerca - Università degli Studi di Pavia
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    Enlighten
    Queen Mary Research Online
    ART

    Measurement of the Higgs boson mass in the H → ZZ ⁎ → 4ℓ decay channel using 139 fb−1 of s = 13 TeV pp collisions recorded by the ATLAS detector at the LHC

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    The mass of the Higgs boson is measured in the H → Z Z∗ → 4 decay channel. The analysis uses proton– proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. The measured value of the Higgs boson mass is 124.99 ± 0.18(stat.) ± 0.04(syst.) GeV. In final states with muons, this measurement benefits from an improved momentum-scale calibration relative to that adopted in previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass of 124.94 ± 0.17(stat.) ± 0.03(syst.) GeV
    University of Liverpool Repository
    Archivio della ricerca - Università degli studi di Napoli "Parthenope"
    Pontificia Universidad Católica de Chile: Repositorio UC
    Crossref
    AIR Universita degli studi di Milano
    Archivio Istituzionale della Ricerca - Università degli Studi di Pavia
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    Enlighten
    Queen Mary Research Online
    ART

    TeV with the ATLAS detector

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    A search for new phenomena giving rise to pairs of opposite electrically charged muons with impact parameters in the millimeter range is presented, using 139 fb−1 of √s = 13 TeV pp collision data from the ATLAS detector at the LHC. The search targets the gap in coverage between existing searches targeting final states with leptons with large displacement and prompt leptons. No significant excess over the background expectation is observed and exclusion limits are set on the mass of long-lived scalar supersymmetric muon-partners (smuons) with much lower lifetimes than previously targeted by displaced muon searches. Smuon lifetimes down to 1 ps are excluded for a smuon mass of 100 GeV, and smuon masses up to 520 GeV are excluded for a proper lifetime of 10 ps, at 95% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Enlighten
    Queen Mary Research Online
    ART
    Portail HAL-PSL
    Crossref
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    Archive ouverte de Sorbonne Université
    Open Access Repository
    Portail HAL Paris 8

    Combination of searches for invisible decays of the Higgs boson using 139 fb−1^{-1} of proton-proton collision data at s=13\sqrt{s} = 13 TeV collected with the ATLAS experiment

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for H→invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb−1 of proton–proton collisions at a centre–of–mass energy of Image 1 at the LHC. In combination with the results at Image 2 and Image 3, an upper limit on the H→invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons.Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for H →\rightarrow invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb−1^{-1} of proton-proton collisions at a centre-of-mass energy of s=13\sqrt{s} =13 TeV at the LHC. In combination with the results at s=7\sqrt{s} =7 TeV and 8 TeV, an upper limit on the H →\rightarrow invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Enlighten
    Queen Mary Research Online
    ART
    Archivio istituzionale della ricerca - Università di Genova
    Portail HAL-PSL
    Archives ouvertes de Paris-Saclay
    Archivio della ricerca - Università degli studi di Napoli "Parthenope"
    Crossref
    Archivio Istituzionale della Ricerca - Università degli Studi di Pavia
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    Archivio della Ricerca - Università di Roma 3
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    CERN Document Server
    Open Access Repository

    Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    Parton energy loss in the quark–gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb−1 of Pb+Pb data and 260 pb−1 of pp data, both at √sNN = 5.02 TeV, with the ATLAS detector. The process pp → γ +jet+X and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum (pT) above 50 GeV and reported as a function of jet pT. This selection results in a sample of jets with a steeply falling pT distribution that are mostly initiated by the showering of quarks. The pp and Pb+Pb measurements are used to report the nuclear modification factor, RAA, and the fractional energy loss, Sloss, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The RAA and Sloss values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. The results are also compared with a variety of theoretical models of colour-charge-dependent energy loss
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Crossref
    Archivio Istituzionale della Ricerca - Università degli Studi di Pavia
    Directory of Open Access Journals
    Archivio della Ricerca - Università di Pisa
    eScholarship - University of California
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    Enlighten
    Queen Mary Research Online

    Measurement of the total and differential Higgs boson production cross-sections at √s = 13 TeV with the ATLAS detector by combining the H → ZZ * → 4l and H → γγ decay channels

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H → ZZ * → 4l and H → γγ decay channels. The results are based on a dataset of 139 fb −1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is 55.5−3.8+4.0 pb, consistent with the Standard Model prediction of 55.6 ± 2.5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H → bb ̄ and cc ̄ decay channels. [Figure not available: see fulltext.
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    AIR Universita degli studi di Milano
    Archivio della Ricerca - Università di Pisa

    Search for pairs of muons with small displacements in pp collisions at s=13 TeV with the ATLAS detector

    Author
    Publication venue
    Publication date
    Field of study
    No full text
    A search for new phenomena giving rise to pairs of opposite electrically charged muons with impact parameters in the millimeter range is presented, using 139 fb−1 of s=13 TeV pp collision data from the ATLAS detector at the LHC. The search targets the gap in coverage between existing searches targeting final states with leptons with large displacement and prompt leptons. No significant excess over the background expectation is observed and exclusion limits are set on the mass of long-lived scalar supersymmetric muon-partners (smuons) with much lower lifetimes than previously targeted by displaced muon searches. Smuon lifetimes down to 1 ps are excluded for a smuon mass of 100 GeV, and smuon masses up to 520 GeV are excluded for a proper lifetime of 10 ps, at 95% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    AIR Universita degli studi di Milano
    Archivio della Ricerca - Università di Roma 3
    ePubs: the open archive for STFC research publications
    corecore