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

Pursuit of paired dijet resonances in the Run 2 dataset with ATLAS

New particles with large masses that decay into hadronically interacting particles are predicted by many models of physics beyond the Standard Model. A search for a massive resonance that decays into pairs of dijet resonances is performed using..

Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using s=13 TeV pp collisions with the ATLAS detector

A search is presented for a heavy resonance Y decaying into a Standard Model Higgs boson H and a new particle X in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at..

Search for the Zγ decay mode of new high-mass resonances in pp collisions at s = 13 TeV with the ATLAS detector

This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV

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