Search for lepton-flavor-violating decays of the $Z$ boson into a $\tau$ lepton and a light lepton with the ATLAS detector

Abstract

Direct searches for lepton flavor violation in decays of the $Z$ boson with the ATLAS detector at the LHC are presented. Decays of the $Z$ boson into an electron or a muon and a hadronically decaying $\tau$ lepton are considered. The searches are based on a data sample of proton-proton collisions collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb${}^{-1}$ at a center-of-mass energy of $\sqrt{s}=13$ TeV. No significant excess of events above the expected background is observed, and upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: $\mathcal{B}(Z\to e\tau )<5.8\times 10^{-5}$ and $\mathcal{B}(Z\to \mu \tau )<2.4\times 10^{-5}$. This is the first limit on $\mathcal{B}(Z\to e\tau )$ with ATLAS data. The upper limit on $\mathcal{B}(Z\to \mu \tau )$ is combined with a previous ATLAS result based on 20.3 fb${}^{-1}$ of proton-proton collision data at a center-of-mass energy of $\sqrt{s}=8$ TeV and the combined upper limit at 95% confidence level is $\mathcal{B}(Z\to \mu \tau )<1.3\times 10^{-5}$.

43 pages in total, author list starting page 27, 8 figures, 6 tables, published in Phys. Rev. D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2016-36/

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Cited by in corpus (6)

• Search for charged-lepton-flavour violation in $Z$-boson decays with the ATLAS detector
• Search for the charged lepton flavor violating decay $J/\psi \to e\tau$
• Contributions to $ZZ{V}^{\ast }$ ($V=\gamma ,Z,Z^{\prime }$) couplings from $CP$ violating flavor changing couplings
• Sensitivity of future lepton colliders and low-energy experiments to charged lepton flavor violation from bileptons
• $CP$ violation in the $HZZ$ vertex and left-right asymmetries
• Searches for new phenomena in leptonic final states using the ATLAS detector