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
