CMSPASHIG16043  
Observation of the SM scalar boson decaying to a pair of $\tau$ leptons with the CMS experiment at the LHC  
CMS Collaboration  
May 2017  
Abstract: A search for a standard model scalar boson decaying into a pair of $\tau$ leptons is performed using events recorded in protonproton collisions by the CMS experiment at the LHC in 2016. The dataset corresponds to an integrated luminosity of 35.9 fb$^{1}$ at a centerofmass energy of $\sqrt{s}= $ 13 TeV. The $\tau$ leptons decay semihadronically, or leptonically to an electron or a muon, and the four final states with the largest branching fractions are considered. An excess of events is observed over the expected background prediction with a significance of 4.9 standard deviations for the scalar boson mass $m_{H} = $ 125 GeV, to be compared to an expected significance of 4.7 standard deviations. The best fit of the observed $H \to \tau \tau$ signal cross section times branching fraction for $m_{H}= $ 125 GeV is 1.06$^{+0.25}_{0.24}$ times the standard model expectation.  
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These preliminary results are superseded in this paper, PLB 779 (2018) 283. The superseded preliminary plots can be found here. 
Figures  Summary  Additional Figures  References  CMS Publications 

Figures  
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Figure 1:
Distributions for the signal (top) and typical background processes (bottom) of the two observables chosen in the 0 jet (left), VBF (center), and boosted (right) categories in the $\mu {\tau _{\rm h}} $ final state. The $Z\rightarrow \mu \mu $ background in the 0 jet category is concentrated in the regions where the visible mass is close to 90 GeV and is negligible when the reconstructed $ {\tau _{\rm h}} $ decay mode is 3prongs. The $Z\rightarrow \tau \tau $ background in the VBF category mostly lies at low $m_{jj}$ values whereas the distribution of VBF signal events extends to high $m_{jj}$ values. In the boosted category, the W+jets background, which behaves similarly as the QCD background, is rather flat with respect to $ {m_{\tau \tau }} $, and is concentrated at low $ { {p_{\mathrm {T}}} ^{\tau \tau }} $ values. 
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Figure 1a:
Distribution for the signal of the $m_{\text{vis}}$ variable in the 0 jet category in the $\mu {\tau _{\rm h}} $ final state. 
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Figure 1b:
Distribution for the signal of the $m_{\tau \tau}$ variable in the VBF category in the $\mu {\tau _{\rm h}} $ final state. 
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Figure 1c:
Distribution for the signal of the $m_{\tau \tau}$ variable in the boosted category in the $\mu {\tau _{\rm h}} $ final state. 
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Figure 1d:
Distribution for the $Z\rightarrow \mu \mu $ background process of the $m_{\text{vis}}$ variable in the 0 jet category in the $\mu {\tau _{\rm h}} $ final state. The $Z\rightarrow \mu \mu $ background in the 0 jet category is concentrated in the regions where the visible mass is close to 90 GeV and is negligible when the reconstructed $ {\tau _{\rm h}} $ decay mode is 3prongs. 
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Figure 1e:
Distribution for the $Z\rightarrow \tau \tau $ background process of the $m_{\tau \tau}$ variable in the VBF category in the $\mu {\tau _{\rm h}} $ final state. The $Z\rightarrow \tau \tau $ background in the VBF category mostly lies at low $m_{jj}$ values whereas the distribution of VBF signal events extends to high $m_{jj}$ values. 
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Figure 1f:
Distribution for the W+jets background process of the $m_{\tau \tau}$ variable in the boosted category in the $\mu {\tau _{\rm h}} $ final state. In the boosted category, the W+jets background, which behaves similarly as the QCD background, is rather flat with respect to $ {m_{\tau \tau }} $, and is concentrated at low $ { {p_{\mathrm {T}}} ^{\tau \tau }} $ values. 
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Figure 2:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2a:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2b:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2c:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2d:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2e:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2f:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2g:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2h:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2i:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
png pdf 
Figure 2j:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
png pdf 
Figure 2k:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 2l:
Signalfree control regions used in the maximum likelihood fit, together with the signal regions, to extract the results. These regions control the yields of the W+jets (a,b,c,d), QCD multijet (e,f,g,h,i,j,k), and ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ (l) backgrounds, in the $\mu {\tau _{\rm h}} $ (a,b,e,f), $\mathrm{ e } {\tau _{\rm h}} $ (c,d,g,h), $ {\tau _{\rm h}} {\tau _{\rm h}} $ (i,j,k) or $\mathrm{ e } \mu $ (l) final states. The constraint on the ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ background is obtained in the $\mathrm{ e } \mu $ final state, but propagated to all final states. The constraints on the W+jets and QCD multijet backgrounds obtained in the boosted categories of the $\mu {\tau _{\rm h}} $ and $\mathrm{ e } {\tau _{\rm h}} $ final states are propagated to the VBF categories of these final states. 
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Figure 3:
Observed and predicted 2D distributions in the 0jet category of the $\mathrm{ e } \mu $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 4:
Observed and predicted 2D distributions in the VBF category of the $\mathrm{ e } \mu $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 5:
Observed and predicted 2D distributions in the boosted category of the $\mathrm{ e } \mu $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 6:
Observed and predicted 2D distributions in the 0jet category of the $\mathrm{ e } {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 7:
Observed and predicted 2D distributions in the VBF category of the $\mathrm{ e } {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 8:
Observed and predicted 2D distributions in the boosted category of the $\mathrm{ e } {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 9:
Observed and predicted 2D distributions in the 0jet category of the $\mu {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 10:
Observed and predicted 2D distributions in the VBF category of the $\mu {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 11:
Observed and predicted 2D distributions in the boosted category of the $\mu {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 12:
Observed and predicted 2D distributions in the 0jet category of the $ {\tau _{\rm h}} {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 13:
Observed and predicted 2D distributions in the VBF category of the $ {\tau _{\rm h}} {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 14:
Observed and predicted 2D distributions in the boosted category of the $ {\tau _{\rm h}} {\tau _{\rm h}} $ final state. The normalization of the predicted background distributions corresponds to the result of the global fit. The signal distribution is normalized to its bestfit signal strength. The background histograms are stacked. The "others" background contribution includes events from diboson and singletopquark production, as well as scalar boson decays to a pair of W bosons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. 
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Figure 15:
Distribution of the decimal logarithm of the ratio between the expected signal and the sum of expected signal and expected background in each bin of the mass distributions used to extract the results, in all signal regions. The background contributions are separated by decay channel. The inset shows the corresponding difference between the observed data and expected background distributions divided by the background expectation, as well as the signal expectation divided by the background expectation. 
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Figure 16:
Combined observed and predicted $ {m_{\tau \tau }} $ distributions. The right figure includes the VBF category of the $\mathrm{ e } \mu $, $\mathrm{ e } {\tau _{\rm h}} $ and $\mu {\tau _{\rm h}} $ channels, and the left figure includes all other channels that make use of $ {m_{\tau \tau }} $ and not $ {m_\text {vis}} $. The normalization of the predicted background distributions corresponds to the result of the global fit, while the signal is normalized to its bestfit signal strength. The mass distribution for a constant range of the second dimension of the signal distributions are weighted according to $S/(S+B)$, where $S$ and $B$ are computed, respectively, as the signal or background contribution in the mass distribution excluding the first and last bins. The "others" background contribution includes events from diboson, $t\bar{t}$, and singletopquark production, as well as scalar boson decays to a pair of W bosons and Z bosons decaying to a pair of light leptons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. The inset shows the corresponding difference between the observed data and expected background distributions, together with the signal expectation. The signal normalization is equal to its normalization before reweighting. 
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Figure 16a:
Combined observed and predicted $ {m_{\tau \tau }} $ distribution. The figure includes all channels that make use of $ {m_{\tau \tau }} $ and not $ {m_\text {vis}} $ other than the VBF category of the $\mathrm{ e } \mu $, $\mathrm{ e } {\tau _{\rm h}} $ and $\mu {\tau _{\rm h}} $ channels. The normalization of the predicted background distributions corresponds to the result of the global fit, while the signal is normalized to its bestfit signal strength. The mass distribution for a constant range of the second dimension of the signal distributions are weighted according to $S/(S+B)$, where $S$ and $B$ are computed, respectively, as the signal or background contribution in the mass distribution excluding the first and last bins. The "others" background contribution includes events from diboson, $t\bar{t}$, and singletopquark production, as well as scalar boson decays to a pair of W bosons and Z bosons decaying to a pair of light leptons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. The inset shows the corresponding difference between the observed data and expected background distributions, together with the signal expectation. The signal normalization is equal to its normalization before reweighting. 
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Figure 16b:
Combined observed and predicted $ {m_{\tau \tau }} $ distribution. The figure includes the VBF category of the $\mathrm{ e } \mu $, $\mathrm{ e } {\tau _{\rm h}} $ and $\mu {\tau _{\rm h}} $ channels. The normalization of the predicted background distributions corresponds to the result of the global fit, while the signal is normalized to its bestfit signal strength. The mass distribution for a constant range of the second dimension of the signal distributions are weighted according to $S/(S+B)$, where $S$ and $B$ are computed, respectively, as the signal or background contribution in the mass distribution excluding the first and last bins. The "others" background contribution includes events from diboson, $t\bar{t}$, and singletopquark production, as well as scalar boson decays to a pair of W bosons and Z bosons decaying to a pair of light leptons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. The inset shows the corresponding difference between the observed data and expected background distributions, together with the signal expectation. The signal normalization is equal to its normalization before reweighting. 
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Figure 17:
Local pvalue and significance as a function of the SM scalar boson mass hypothesis. The observation (black) is compared to the expectation (blue) for a scalar boson with a mass $ {m_{\mathrm{ H } }} = $ 125 GeV. The background includes scalar boson decays to a pair of W bosons, with $ {m_{\mathrm{ H } }} = $ 125 GeV. 
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Figure 18:
Bestfit signal strength per category (left) and channel (right), for $ {m_{\mathrm{ H } }} = $ 125 GeV. The constraints from the global fit are used to extract each of the individual bestfit signal strengths. The combined bestfit signal strength is $\hat\mu = $ 1.06 $\pm$ 0.25. 
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Figure 18a:
Bestfit signal strength per category, for $ {m_{\mathrm{ H } }} = $ 125 GeV. The constraints from the global fit are used to extract each of the individual bestfit signal strengths. The combined bestfit signal strength is $\hat\mu = $ 1.06 $\pm$ 0.25. 
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Figure 18b:
Bestfit signal strength per channel, for $ {m_{\mathrm{ H } }} = $ 125 GeV. The constraints from the global fit are used to extract each of the individual bestfit signal strengths. The combined bestfit signal strength is $\hat\mu = $ 1.06 $\pm$ 0.25. 
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Figure 19:
Scan of the negative loglikelihood difference as a function of $\kappa _V$ and $\kappa _f$, for $ {m_{\mathrm{ H } }} = $ 125 GeV. All nuisance parameters are profiled for each point. For this scan, the $pp\rightarrow H$(125 GeV)$\rightarrow WW$ contribution is treated as a signal process. 
Summary 
A search for the SM scalar boson based on data collected in pp collisions by the CMS detector in 2016 at a centerofmass energy of 13 TeV, has been presented. The four di$\tau$ final states with the largest branching fraction have been studied, in event categories targeting Higgs boson signal events produced via gluongluon fusion and vector boson fusion. The results are extracted via twodimensional maximum likelihood fits in the planes defined by the full or visible di$\tau$ mass, and the lepton transverse momentum or $\tau_{\mathrm{h}}$ reconstructed decay mode in the 0jet category, the invariant mass of the dijets in the VBF category, and the scalar boson candidate transverse momentum in the boosted category. This leads to the observation of decays of the SM scalar boson to pairs of $\tau$ leptons, with an observed significance of 4.9 standard deviations for a mass of 125 GeV. This is to be compared with an expected significance of 4.7 standard deviations. 
Additional Figures  
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Additional Figure 1:
Normalized distributions of the visible mass, $ {m_\text {vis}} $, and of the SVfit mass, $ {m_{\tau \tau }} $, for a signal sample with a SM scalar boson of mass $ {m_{\mathrm{ H } }} = $ 125 GeV decaying to a pair of $\tau $ leptons in the $\mu {\tau _{\rm h}} $ final state. 
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Additional Figure 2:
Observed and expected distributions of the transverse mass between the muon and $ {E_{\mathrm {T}}^{\text {miss}}} $, in the $\mu {\tau _{\rm h}} $ final state. The selection is inclusive in the number of jets. The background distributions have not been fitted to the data. The electroweak component of the background includes W+jets, single top quark, and diboson production events. 
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Additional Figure 3:
Combined observed 95% CL upper limit on the signal strength parameter $\mu $, together with the expected limit obtained in the backgroundonly hypothesis. The uncertainty bands show the expected one and twostandarddeviation probability intervals around the expected limit. Scalar boson decays to pairs of W bosons are considered as a background. 
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Additional Figure 4:
Observed 95% CL upper limit on the signal strength parameter $\mu $, in the $\mathrm{ e } \mu $ (a), $\mathrm{ e } {\tau _{\rm h}} $ (b), $\mu {\tau _{\rm h}} $ (c), and $ {\tau _{\rm h}} {\tau _{\rm h}} $ (d) final states, together with the expected limit obtained in the backgroundonly hypothesis. The uncertainty bands show the expected one and twostandarddeviation probability intervals around the expected limit. Scalar boson decays to pairs of W bosons are considered as a background. 
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Additional Figure 4a:
Observed 95% CL upper limit on the signal strength parameter $\mu $, in the $\mathrm{ e } \mu $ final state, together with the expected limit obtained in the backgroundonly hypothesis. The uncertainty bands show the expected one and twostandarddeviation probability intervals around the expected limit. Scalar boson decays to pairs of W bosons are considered as a background. 
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Additional Figure 4b:
Observed 95% CL upper limit on the signal strength parameter $\mu $, in the $\mathrm{ e } {\tau _{\rm h}} $ final state, together with the expected limit obtained in the backgroundonly hypothesis. The uncertainty bands show the expected one and twostandarddeviation probability intervals around the expected limit. Scalar boson decays to pairs of W bosons are considered as a background. 
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Additional Figure 4c:
Observed 95% CL upper limit on the signal strength parameter $\mu $, in the $\mu {\tau _{\rm h}} $ final state, together with the expected limit obtained in the backgroundonly hypothesis. The uncertainty bands show the expected one and twostandarddeviation probability intervals around the expected limit. Scalar boson decays to pairs of W bosons are considered as a background. 
png pdf 
Additional Figure 4d:
Observed 95% CL upper limit on the signal strength parameter $\mu $, in the $ {\tau _{\rm h}} {\tau _{\rm h}} $ final state, together with the expected limit obtained in the backgroundonly hypothesis. The uncertainty bands show the expected one and twostandarddeviation probability intervals around the expected limit. Scalar boson decays to pairs of W bosons are considered as a background. 
png pdf 
Additional Figure 5:
Distribution of the decimal logarithm of the ratio between the expected signal and the sum of expected signal and expected background in each bin of the mass distributions used to extract the results, in all signal regions. The background contributions are separated by process (a) or by category (b). The inset shows the corresponding difference between the observed data and expected background distributions divided by the background expectation, as well as the signal expectation divided by the background expectation. 
png pdf 
Additional Figure 5a:
Distribution of the decimal logarithm of the ratio between the expected signal and the sum of expected signal and expected background in each bin of the mass distributions used to extract the results, in all signal regions. The background contributions are separated by process. The inset shows the corresponding difference between the observed data and expected background distributions divided by the background expectation, as well as the signal expectation divided by the background expectation. 
png pdf 
Additional Figure 5b:
Distribution of the decimal logarithm of the ratio between the expected signal and the sum of expected signal and expected background in each bin of the mass distributions used to extract the results, in all signal regions. The background contributions are separated by category. The inset shows the corresponding difference between the observed data and expected background distributions divided by the background expectation, as well as the signal expectation divided by the background expectation. 
png pdf 
Additional Figure 6:
Combined observed and predicted $ {m_\text {vis}} $ distributions, in the 0jet category of the $\mathrm{ e } \mu $, $\mathrm{ e } {\tau _{\rm h}} $, and $\mu {\tau _{\rm h}} $ channels. The normalization of the predicted background distributions corresponds to the result of the global fit, while the signal is normalized to its bestfit signal strength. The mass distributions for a constant range of the second dimension of the signal distributions are weighted according to $S/(S+B)$, where $S$ and $B$ are computed, respectively, as the signal or background contribution in the mass distribution excluding the first and last bins. The "others" background contribution includes events from diboson, $\mathrm{ t \bar{t} }$, and singletopquark production, as well as scalar boson decays to a pair of W bosons and Z bosons decaying to a pair of light leptons. The background uncertainty band accounts for all sources of background uncertainties, systematic as well as statistical, after the global fit. The inset shows the corresponding difference between the observed data and expected background distributions, together with the signal expectation. The signal normalization after reweighting is equal to its normalization before reweighting, by construction. 
png pdf 
Additional Figure 7:
Profile likelihood ratio as a function of the signal strength parameter. The solid curve represents the observed profile likelihood ration. The green line is obtained by removing the theoryrelated uncertainties, the blue line by further removing the binbybin background statistical uncertainties, and the red one by keeping only the statistical uncertainties. 
png pdf 
Additional Figure 8:
Expected 95% CL upper limits on the signal strength parameter for the $\mathrm{ e } \mu $, $\mathrm{ e } {\tau _{\rm h}} $, $\mu {\tau _{\rm h}} $, and $ {\tau _{\rm h}} {\tau _{\rm h}} $ channels, together with the expected combined upper limit. 
png pdf 
Additional Figure 9:
Bestfit signal strength for the ggH production, and for the other production modes, for $ {m_{\mathrm{ H } }} = 125$ GeV. The constraints from the global fit are used to extract each of the individual bestfit signal strengths. The combined bestfit signal strength is $\hat\mu = $ 1.06 $\pm$ 0.25. 
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