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

The 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

• #### Combined NN output in SR, $e\tau_\mu$ low-$p_\text{T}$

Data from Figure 1a of the paper

10.17182/hepdata.105516.v1/t1

The best-fit predicted and observed distributions of the combined NN output in the low-$p_\text{T}$-SR for the $e\tau_\mu$ channel. The first...

• #### Combined NN output in SR, $\mu\tau_e$ low-$p_\text{T}$

Data from Figure 1b of the paper

10.17182/hepdata.105516.v1/t2

The best-fit predicted and observed distributions of the combined NN output in the low-$p_\text{T}$-SR for the $\mu\tau_e$ channel. The first...

• #### Combined NN output in SR, $e\tau_\mu$ high-$p_\text{T}$

Data from Figure 1c of the paper

10.17182/hepdata.105516.v1/t3

The best-fit predicted and observed distributions of the combined NN output in the high-$p_\text{T}$-SR for the $e\tau_\mu$ channel. The first...

• #### Combined NN output in SR, $\mu\tau_e$ high-$p_\text{T}$

Data from Figure 1d of the paper

10.17182/hepdata.105516.v1/t4

The best-fit predicted and observed distributions of the combined NN output in the high-$p_\text{T}$-SR for the $\mu\tau_e$ channel. The first...

• #### Collinear mass in SR, $e\tau_\mu$ high-$p_\text{T}$

Data from Figure 2a of the paper

10.17182/hepdata.105516.v1/t5

The best-fit predicted and observed distributions of the collinear mass $m_\text{coll}$ in the high-$p_\text{T}$-SR for the $e\tau_\mu$ channel. The first...

• #### Collinear mass in SR, $\mu\tau_e$ high-$p_\text{T}$

Data from Figure 2b of the paper

10.17182/hepdata.105516.v1/t6

The best-fit predicted and observed distributions of the collinear mass $m_\text{coll}$ in the high-$p_\text{T}$-SR for the $\mu\tau_e$ channel. The first...

• #### Upper limits on $\mathcal{B}(Z\to\ell\tau)$, $\tau\to\ell\nu\nu$

Data from Table 3 of the paper

10.17182/hepdata.105516.v1/t7

Observed and expected upper limits on $\mathcal{B}(Z\rightarrow\ell\tau)$ with leptonically decaying $\tau$ at 95% confidence level.

• #### Upper limits on $\mathcal{B}(Z\rightarrow\ell\tau)$, combined

Data from Table 3 of the paper

10.17182/hepdata.105516.v1/t8

Observed and expected upper limits on $\mathcal{B}(Z\rightarrow\ell\tau)$ at 95% confidence level, combination of hadronically and leptonically decaying $\tau$ channels.

• #### Collinear mass in CRZ$\tau\tau$, $e\tau_\mu$

Data from Figure 7a of the auxiliary material

10.17182/hepdata.105516.v1/t9

The best-fit predicted and observed distributions of the collinear mass $m_\text{coll}$ in the CRZ$\tau\tau$ for the $e\tau_\mu$ channel. The first...

• #### Collinear mass in CRZ$\tau\tau$, $\mu\tau_e$

Data from Figure 7b of the auxiliary material

10.17182/hepdata.105516.v1/t10

The best-fit predicted and observed distributions of the collinear mass $m_\text{coll}$ in the CRZ$\tau\tau$ for the $\mu\tau_e$ channel. The first...

• #### Combined NN output in CRZ$\tau\tau$, $e\tau_\mu$

Data from Figure 7c of the auxiliary material

10.17182/hepdata.105516.v1/t11

The best-fit predicted and observed distributions of the combined NN output in the CRZ$\tau\tau$ for the $e\tau_\mu$ channel. The first...

• #### Combined NN output in CRZ$\tau\tau$, $\mu\tau_e$

Data from Figure 7d of the auxiliary material

10.17182/hepdata.105516.v1/t12

The best-fit predicted and observed distributions of the combined NN output in the CRZ$\tau\tau$ for the $\mu\tau_e$ channel. The first...

• #### Electron transverse momentum (SR), $e\tau_\mu$ high-$p_\text{T}$

Data from Figure 8a of the auxiliary material

10.17182/hepdata.105516.v1/t13

The best-fit predicted and observed distributions of the leading lepton transverse momentum $p_\text{T}(e)$ in the high-$p_\text{T}$-SR for the $e\tau_\mu$ channel....

• #### Muon transverse momentum in SR, $\mu\tau_e$ high-$p_\text{T}$

Data from Figure 8b of the auxiliary material

10.17182/hepdata.105516.v1/t14

The best-fit predicted and observed distributions of the leading lepton transverse momentum $p_\text{T}(\mu)$ in the high-$p_\text{T}$-SR for the $\mu\tau_e$ channel....

• #### Missing transverse momentum in SR, $e\tau_\mu$ low-$p_\text{T}$

Data from Figure 8c of the auxiliary material

10.17182/hepdata.105516.v1/t15

The best-fit predicted and observed distributions of the missing transverse momentum $E^\text{miss}_\text{T}$ in the low-$p_\text{T}$-SR for the $e\tau_\mu$ channel. The...

• #### Missing transverse momentum in SR, $\mu\tau_e$ low-$p_\text{T}$

Data from Figure 8d of the auxiliary material

10.17182/hepdata.105516.v1/t16

The best-fit predicted and observed distributions of the missing transverse momentum $E^\text{miss}_\text{T}$ in the low-$p_\text{T}$-SR for the $\mu\tau_e$ channel. The...