Tools for estimating fake/non-prompt lepton backgrounds with the ATLAS detector at the LHC

International audienceMeasurements and searches performed with the ATLAS detector at the CERN LHC often involve signatures with one or more prompt leptons. Such analysesare subject to `fake/non-prompt' lepton backgrounds, where either a hadron or a lepton from a hadron decay or an electron from a photon conversion satisfies the prompt-leptonselection criteria. These backgrounds often arise within a hadronic jet because of particle decays in the showering process, particle misidentification or particleinteractions with the detector material. As it is challenging to model these processes with high accuracy in simulation, their estimation typically uses data-driven methods.Three methods for carrying out this estimation are described, along with their implementation in ATLAS and their performance

Search for exclusive Higgs and Z boson decays to ωγ and Higgs boson decays to K ⁎ γ with the ATLAS detector

Searches for the exclusive decays of the Higgs boson to an ω meson and a photon or a K⁎ meson and a photon can probe flavour-conserving and flavour-violating Higgs boson couplings to light quarks, respectively. Searches for these decays, along with the analogous Z boson decay to an ω meson and a photon, are performed with a pp collision data sample corresponding to integrated luminosities of up to 134 fb−1 collected at √s=13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The obtained 95% confidence-level upper limits on the respective branching fractions are B(H→ωγ)<5.5×10−4, B(H→K⁎γ)<2.2×10−4 and B(Z→ωγ)<3.9×10−6. The limits for H→ωγ and Z→ωγ are 370 times and 140 times the Standard Model expected values, respectively. The result for Z→ωγ corresponds to a two-orders-of-magnitude improvement over the limit obtained by the DELPHI experiment at LEP