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| CMS-HIG-20-009 ; CERN-EP-2021-061 | ||
| Search for lepton-flavor violating decays of the Higgs boson in the $\mu\tau $ and e$\tau $ final states in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 7 May 2021 | ||
| Phys. Rev. D 104 (2021) 032013 | ||
| Abstract: A search is presented for lepton-flavor violating decays of the Higgs boson to $\mu\tau$ and e$\tau $. The data set corresponds to an integrated luminosity of 137 fb$^{-1}$ collected at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. No significant excess has been found, and the results are interpreted in terms of upper limits on lepton-flavor violating branching fractions of the Higgs boson. The observed (expected) upper limits on the branching fractions are, respectively, ${\mathcal{B}(\mathrm{H}\to\mu\tau)} < $ 0.15 (0.15)% and ${\mathcal{B}(\mathrm{H}\to\mathrm{e}\tau)} < $ 0.22 (0.16)% at 95% confidence level. | ||
| Links: e-print arXiv:2105.03007 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Collinear mass distributions for the data and background processes. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% and $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% are assumed for the two signal processes. The channels are ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$ (upper row left), ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$ (upper row right), ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$ (lower row left), and ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$ (lower row right). The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the statistical and systematic uncertainties are added in quadrature. |
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Figure 1-a:
Collinear mass distributions for the data and background processes. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% and $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% are assumed for the two signal processes. The channel is ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the statistical and systematic uncertainties are added in quadrature. |
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Figure 1-b:
Collinear mass distributions for the data and background processes. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% and $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% are assumed for the two signal processes. The channel is ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the statistical and systematic uncertainties are added in quadrature. |
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Figure 1-c:
Collinear mass distributions for the data and background processes. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% and $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% are assumed for the two signal processes. The channel is ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the statistical and systematic uncertainties are added in quadrature. |
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Figure 1-d:
Collinear mass distributions for the data and background processes. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% and $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% are assumed for the two signal processes. The channel is ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the statistical and systematic uncertainties are added in quadrature. |
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Figure 2:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jets (upper row left), 1 jet (upper row right), 2 jets ggH (lower row left), and 2 jets VBF (lower row right). The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 2-a:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jet. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 2-b:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 1 jet. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 2-c:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets ggH. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 2-d:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets VBF. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 3:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jets (upper row left), 1 jet (upper row right), 2 jets ggH (lower row left), and 2 jets VBF (lower row right). The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 3-a:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jet. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 3-b:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 1 jet. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 3-c:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets ggH. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 3-d:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mu \tau _{\mathrm{e}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets VBF. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 4:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jets (upper row left), 1 jet (upper row right), 2 jets ggH (lower row left), and 2 jets VBF (lower row right). The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 4-a:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jet. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 4-b:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 1 jet. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 4-c:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets ggH. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 4-d:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} {\tau _\mathrm {h}}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets VBF. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 5:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jets (upper row left), 1 jet (upper row right), 2 jets ggH (lower row left), and 2 jets VBF (lower row right). The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 5-a:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 0 jet. The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 5-b:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 1 jet. The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 5-c:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets ggH. The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 5-d:
BDT discriminant distributions for the data and background processes in the ${\mathrm{H} \to \mathrm{e} \tau _{\mu}}$ channel. A $ {\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)} =$ 20% is assumed for the signal. The channel categories are 2 jets VBF. The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 6:
The ${m_{\text {col}}}$ distribution in VR with same electric charge for both leptons (left), W+jets VR (middle), and ${\mathrm{t} {}\mathrm{\bar{t}}}$ VR (right). In each distribution, the VR's dominant background is shown, and all the other backgrounds are grouped into "Other bkg.''. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The lower panel in each plot shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 6-a:
The ${m_{\text {col}}}$ distribution in VR with same electric charge for both leptons. The VR's dominant background is shown, and all the other backgrounds are grouped into "Other bkg.''. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 6-b:
The ${m_{\text {col}}}$ distribution in the W+jets VR. The VR's dominant background is shown, and all the other backgrounds are grouped into "Other bkg.''. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 6-c:
The ${m_{\text {col}}}$ distribution in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ VR. The VR's dominant background is shown, and all the other backgrounds are grouped into "Other bkg.''. A $ {\mathcal {B}(\mathrm{H} \to \mu \tau)} =$ 20% is assumed for the signal. The lower panel shows the ratio of data and estimated background. The uncertainty band corresponds to the background uncertainty in which the post-fit statistical and systematic uncertainties are added in quadrature. |
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Figure 7:
Observed (expected) 95% CL upper limits on the ${\mathcal {B}(\mathrm{H} \to \mu \tau)}$ (left) and ${\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)}$ (right) for each individual category and combined. The categories from top to bottom row are ${\mu {\tau _\mathrm {h}}}$ 0Jets, ${\mu {\tau _\mathrm {h}}}$ 1Jet, ${\mu {\tau _\mathrm {h}}}$ 2 Jets, ${\mu {\tau _\mathrm {h}}}$ VBF, ${\mu \tau _{\mathrm{e}}}$ 0Jets, ${\mu \tau _{\mathrm{e}}}$ 1Jet, ${\mu \tau _{\mathrm{e}}}$ 2 Jets, ${\mu \tau _{\mathrm{e}}}$ VBF, and ${\mu \tau}$ combined (left) and e${\tau _\mathrm {h}}$ 0Jets, e${\tau _\mathrm {h}}$ 1Jet, e${\tau _\mathrm {h}}$ 2 Jets, e${\tau _\mathrm {h}}$ VBF, e$ \tau _{\mu}$ 0Jets, e$ \tau _{\mu}$ 1Jet, e$ \tau _{\mu}$ 2 Jets, e$ \tau _{\mu}$ VBF, and e$\tau$ combined (right). |
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Figure 7-a:
Observed (expected) 95% CL upper limits on the ${\mathcal {B}(\mathrm{H} \to \mu \tau)}$ for each individual category and combined. The categories from top to bottom row are ${\mu {\tau _\mathrm {h}}}$ 0Jets, ${\mu {\tau _\mathrm {h}}}$ 1Jet, ${\mu {\tau _\mathrm {h}}}$ 2 Jets, ${\mu {\tau _\mathrm {h}}}$ VBF, ${\mu \tau _{\mathrm{e}}}$ 0Jets, ${\mu \tau _{\mathrm{e}}}$ 1Jet, ${\mu \tau _{\mathrm{e}}}$ 2 Jets, ${\mu \tau _{\mathrm{e}}}$ VBF, and ${\mu \tau}$ combined. |
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Figure 7-b:
Observed (expected) 95% CL upper limits on the ${\mathcal {B}(\mathrm{H} \to \mathrm{e} \tau)}$ for each individual category and combined. The categories from top to bottom row are e${\tau _\mathrm {h}}$ 0Jets, e${\tau _\mathrm {h}}$ 1Jet, e${\tau _\mathrm {h}}$ 2 Jets, e${\tau _\mathrm {h}}$ VBF, e$ \tau _{\mu}$ 0Jets, e$ \tau _{\mu}$ 1Jet, e$ \tau _{\mu}$ 2 Jets, e$ \tau _{\mu}$ VBF, and e$\tau$ combined. |
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Figure 8:
Expected (red line) and observed (black solid line) 95% CL upper limits on the LFV Yukawa couplings, $ {{| Y_{\mu \tau} |}} $ vs. $ {{| Y_{\tau \mu} |}} $ (left) and $ {{| Y_{\mathrm{e} \tau} |}} $ vs. $ {{| Y_{\tau \mathrm{e}} |}} $ (right). The $ {{| Y_{\mu \tau} |}} $ or $ {{| Y_{\mathrm{e} \tau} |}} $ couplings correspond to left chiral muon or electron and right chiral $\tau$ lepton, while $ {{| Y_{\tau \mu} |}} $ or $ {{| Y_{\tau \mathrm{e}} |}} $ couplings correspond to left chiral $\tau$ lepton and right chiral muon or electron. In the left plot, the expected limit is covered by the observed limit as they have similar values. The flavor diagonal Yukawa couplings are approximated by their SM values. The green and yellow bands indicate the range that is expected to contain 68% and 95% of all observed limit variations from the expected limit. The shaded regions are constraints obtained from null searches for $\tau \to 3\mu $ or $\tau \to 3\mathrm{e} $ (dark blue) [92] and $\tau \to \mu \gamma $ or $\tau \to \mathrm{e} \gamma $ (purple) [93]. The blue diagonal line is the theoretical naturalness limit $ {| Y_{ij}Y_{ji} |} = {m_i}m_j/v^2$ [11]. |
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Figure 8-a:
Expected (red line) and observed (black solid line) 95% CL upper limits on the LFV Yukawa couplings, $ {{| Y_{\mu \tau} |}} $ vs. $ {{| Y_{\tau \mu} |}} $. The $ {{| Y_{\mu \tau} |}} $ or $ {{| Y_{\mathrm{e} \tau} |}} $ couplings correspond to left chiral muon or electron and right chiral $\tau$ lepton, while $ {{| Y_{\tau \mu} |}} $ or $ {{| Y_{\tau \mathrm{e}} |}} $ couplings correspond to left chiral $\tau$ lepton and right chiral muon or electron. The expected limit is covered by the observed limit as they have similar values. The flavor diagonal Yukawa couplings are approximated by their SM values. The green and yellow bands indicate the range that is expected to contain 68% and 95% of all observed limit variations from the expected limit. The shaded regions are constraints obtained from null searches for $\tau \to 3\mu $ or $\tau \to 3\mathrm{e} $ (dark blue) [92] and $\tau \to \mu \gamma $ or $\tau \to \mathrm{e} \gamma $ (purple) [93]. The blue diagonal line is the theoretical naturalness limit $ {| Y_{ij}Y_{ji} |} = {m_i}m_j/v^2$ [11]. |
png pdf |
Figure 8-b:
Expected (red line) and observed (black solid line) 95% CL upper limits on the LFV Yukawa couplings, $ {{| Y_{\mathrm{e} \tau} |}} $ vs. $ {{| Y_{\tau \mathrm{e}} |}} $. The $ {{| Y_{\mu \tau} |}} $ or $ {{| Y_{\mathrm{e} \tau} |}} $ couplings correspond to left chiral muon or electron and right chiral $\tau$ lepton, while $ {{| Y_{\tau \mu} |}} $ or $ {{| Y_{\tau \mathrm{e}} |}} $ couplings correspond to left chiral $\tau$ lepton and right chiral muon or electron. The flavor diagonal Yukawa couplings are approximated by their SM values. The green and yellow bands indicate the range that is expected to contain 68% and 95% of all observed limit variations from the expected limit. The shaded regions are constraints obtained from null searches for $\tau \to 3\mu $ or $\tau \to 3\mathrm{e} $ (dark blue) [92] and $\tau \to \mu \gamma $ or $\tau \to \mathrm{e} \gamma $ (purple) [93]. The blue diagonal line is the theoretical naturalness limit $ {| Y_{ij}Y_{ji} |} = {m_i}m_j/v^2$ [11]. |
| Tables | |
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Table 1:
Event selection criteria for the ${\mathrm{H} \to \mu \tau}$ channels. |
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Table 2:
Event selection criteria for the ${\mathrm{H} \to \mathrm{e} \tau}$ channels. |
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Table 3:
Systematic uncertainties in the expected event yields. All uncertainties are treated as correlated among categories, except those with two values separated by the $\oplus $ sign. In this case, the first value is the correlated uncertainty and the second value is the uncorrelated uncertainty for each category. |
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Table 4:
Observed and expected upper limits at 95% CL and best fit branching fractions for each individual jet category, and their combinations, in the ${\mathrm{H} \to \mu \tau}$ channel. |
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Table 5:
Observed and expected upper limits at 95% CL and best fit branching fractions for each individual jet category, and their combinations, in the ${\mathrm{H} \to \mathrm{e} \tau}$ channel. |
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Table 6:
Summary of observed and expected upper limits at 95% CL, best fit branching fractions and corresponding constraints on Yukawa couplings for the ${\mathrm{H} \to \mu \tau}$ and ${\mathrm{H} \to \mathrm{e} \tau}$ channels. |
| Summary |
| A search for lepton-flavor violation has been performed in the $\mu\tau$ and e$\tau$ final states of the Higgs boson in data collected by the CMS experiment. The data correspond to an integrated luminosity of 137 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV. The results are extracted through a maximum likelihood fit to a boosted decision tree output, trained to distinguish the expected signal from backgrounds. The observed (expected) upper limits on the branching fraction of the Higgs boson to $\mu\tau$ are 0.15 (0.15)% and to e$\tau$ are 0.22 (0.16)%, respectively, at 95% confidence level. Upper limits on the off-diagonal $\mu\tau$ and e$\tau$ couplings are derived from these constraints, $\sqrt{\smash[b]{|Y_{\mu\tau}| ^{2}+|{Y_{\tau\mu}}| ^{2}}} < $ 1.11 ${\times}10^{-3}$ and $\sqrt{\smash[b]{|{Y_{\mathrm{e}\tau}}| ^{2}+|{Y_{\tau\mathrm{e}}}| ^{2}}} < $ 1.35 ${\times}10^{-3}$. These results constitute an improvement over the previous limits from CMS and ATLAS experiments. |
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