SciPost Phys. Proc. 17, 013 (2025) ·
published 23 July 2025
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Three analyses exploiting the $H→\tau\tau$ process using 139 fb$^{-1}$ of proton--proton collision data collected at a center-of-mass energy of 13 TeV by the ATLAS detector at the LHC are presented. A measurement of $VH$ production, with $V(=W, Z)→ e\nu/\mu\nu,ee/\mu\mu$ decays, has established the first evidence for this process with an observed (expected) significance of 4.2 (3.6) standard deviations. The second analysis, first of its kind by the ATLAS collaboration, probes CP-invariance if the decay products of the $\tau$ leptons using an angular observable $\phi_\tau$, and measured an observed (expected) value of $\phi_\tau=9 ± 16^\circ (0 ± 28^\circ)$ at 68% confidence level. The last analysis is a search for lepton-flavour-violation in $H→ e\tau/\mu\tau$ decays, where most stringent exclusion limits at 95% confidence level on $H→ e\tau$ branching ratio of 0.2%, is obtained.
SciPost Phys. Proc. 8, 116 (2022) ·
published 13 July 2022
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Two measurements and their combination for the $t\bar{t}t\bar{t}$ production cross-section analysis using 139 fb$^{-1}$ of proton$-$proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC are presented. The first analysis uses the final states with either one or two opposite-sign leptons (electrons or muons). In the second analysis the final states with either two same-sign or at least three leptons are considered. With an observed (expected) significance of 4.3 (2.4) standard deviations over the background-only hypothesis, the second analysis provides the first evidence for the $t\bar{t}t\bar{t}$ process. No significant deviations from the Standard Model are observed.
