Searching for rare and forbidden exclusive Higgs boson decays with the Atlas detector

Searches for Higgs and Z bosons decaying to an ω meson and a photon, and for Higgs bosons decaying to a K$^∗$ and a photon are discussed using proton collision data recorded by the ATLAS experiment at √s = 13 TeV between 2016 and 2018. The observed events are consistent with the expected background. The obtained 95% confidence level upper limit on the branching ratio for the H → ωγ decay using 89.5 fb$^{−1}$ of data is 1.0 ×10$^{−4}$ assuming a Standard Model Higgs Boson production. The analogous limit obtained for the Z → ωγ decay is 3.5 ×10${−7}$. The obtained upper limit for the H → K$^∗$γ decay is 8.9 ×10$^{−5}$, using 134 fb$^{−1}$ of data. The search for H → K$^∗$γ represents the first search for a flavour-violating exclusive decay of the Higgs boson

Operation and performance of the ATLAS semiconductor tracker in LHC Run 2

Abstract The semiconductor tracker (SCT) is one of the tracking systems for charged particles in the ATLAS detector. It consists of 4088 silicon strip sensor modules. During Run 2 (2015–2018) the Large Hadron Collider delivered an integrated luminosity of 156 fb-1 to the ATLAS experiment at a centre-of-mass proton-proton collision energy of 13 TeV. The instantaneous luminosity and pile-up conditions were far in excess of those assumed in the original design of the SCT detector. Due to improvements to the data acquisition system, the SCT operated stably throughout Run 2. It was available for 99.9% of the integrated luminosity and achieved a data-quality efficiency of 99.85%. Detailed studies have been made of the leakage current in SCT modules and the evolution of the full depletion voltage, which are used to study the impact of radiation damage to the modules.</jats:p