Search for lepton-flavor-violation in $Z$-boson decays with $\tau$-leptons with the ATLAS detector

The ATLAS collaboration
CERN-EP-2021-067, 2021.

Abstract (data abstract)
CERN-LHC. Search for lepton-flavor-violating $Z\to e\tau$ and $Z\to\mu\tau$ decays with 139 fb$^{-1}$ of Run 2 $pp$ collision data at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. This search exploits leptonically-decaying taus in the final state and is combined with a similar ATLAS search in the final state in which the tau-lepton decays hadronically using the same data set as well as Run 1 data. Final states with an opposite-sign electron-muon pair are considered. The fiducial region of the $e\tau$ channel is defined as: - Opposite-sign electron-muon pair - $p_{\mathrm{T}}(e)$ > 27 GeV - $p_{\mathrm{T}}(\mu)$ > 10 GeV - $p_{\mathrm{T}}(e)$ > $p_{\mathrm{T}}(\mu)$ - Veto on 1.37 < $|\eta(e)|$ < 1.52 - $\Delta R(e,\mu)$ > 0.1 - $|\Delta\phi(e,E^{\mathrm{miss}}_{\mathrm{T}})|$ > 1 - Visible mass $m_{\mathrm{vis}}(e,\mu)$ > 40 GeV - No $b$-jets - Transverse mass $m_{\mathrm{T}}(\mu,E^{\mathrm{miss}}_{\mathrm{T}})$ < 35 GeV The fiducial region of the $\mu\tau$ channel is defined as: - Opposite-sign electron-muon pair - $p_{\mathrm{T}}(e)$ > 15 GeV - $p_{\mathrm{T}}(\mu)$ > 27 GeV - $p_{\mathrm{T}}(\mu)$ > $p_{\mathrm{T}}(e)$ - Veto on 1.37 < $|\eta(e)|$ < 1.52 - $\Delta R(e,\mu)$ > 0.1 - $|\Delta\phi(\mu,E^{\mathrm{miss}}_{\mathrm{T}})|$ > 1 - Visible mass $m_{\mathrm{vis}}(e,\mu)$ > 40 GeV - No $b$-jets - Transverse mass $m_{\mathrm{T}}(e,E^{\mathrm{miss}}_{\mathrm{T}})$ < 35 GeV

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