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| CMS-EXO-16-008 ; CERN-EP-2016-273 | ||
| Search for heavy resonances decaying to tau lepton pairs in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 20 November 2016 | ||
| JHEP 02 (2017) 048 | ||
| Abstract: A search for heavy resonances that decay to tau lepton pairs is performed using proton-proton collisions at $\sqrt{s} = $ 13 TeV. The data were collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 2.2 fb$^{-1}$. The observations are in agreement with standard model predictions. An upper limit at 95% confidence level on the product of the production cross section and branching fraction into tau lepton pairs is calculated as a function of the resonance mass. For the sequential standard model, the presence of Z' bosons decaying into tau lepton pairs is excluded for Z' masses below 2.1 TeV, extending previous limits for this final state. For the topcolor-assisted technicolor model, which predicts Z' bosons that preferentially couple to third-generation fermions, Z' masses below 1.7 TeV are excluded, representing the most stringent limit to date. | ||
| Links: e-print arXiv:1611.06594 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Observed ${m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )}$ distribution in the signal region compared to the expected SM backgrounds for the (top left) ${\tau _\mathrm{ e } \tau _\mu } $, (top right) ${\tau _\mathrm{ e } \tau _{\mathrm {h}}} $, (bottom left) ${\tau _\mu \tau _{\mathrm {h}}} $, and (bottom right) ${ {\tau _{\mathrm {h}}} {\tau _{\mathrm {h}}} }$ channels. The dashed histogram shows the distribution expected for a ${\mathrm{ Z }' _{\mathrm {SSM}}}$ boson with mass 1500 GeV. The rightmost bins also include events with $ {m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )} >$ 900 GeV, and are normalized to the displayed bin width. The lower panel shows the ratio of the observed number of events to the total background prediction. The shaded bands represent the total uncertainty in the background prediction. |
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Figure 1-a:
Observed ${m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )}$ distribution in the signal region compared to the expected SM backgrounds for the ${\tau _\mathrm{ e } \tau _\mu } $ channel. The dashed histogram shows the distribution expected for a ${\mathrm{ Z }' _{\mathrm {SSM}}}$ boson with mass 1500 GeV. The rightmost bins also include events with $ {m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )} >$ 900 GeV, and are normalized to the displayed bin width. The lower panel shows the ratio of the observed number of events to the total background prediction. The shaded bands represent the total uncertainty in the background prediction. |
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Figure 1-b:
Observed ${m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )}$ distribution in the signal region compared to the expected SM backgrounds for the ${\tau _\mathrm{ e } \tau _{\mathrm {h}}} $ channel. The dashed histogram shows the distribution expected for a ${\mathrm{ Z }' _{\mathrm {SSM}}}$ boson with mass 1500 GeV. The rightmost bins also include events with $ {m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )} >$ 900 GeV, and are normalized to the displayed bin width. The lower panel shows the ratio of the observed number of events to the total background prediction. The shaded bands represent the total uncertainty in the background prediction. |
png pdf |
Figure 1-c:
Observed ${m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )}$ distribution in the signal region compared to the expected SM backgrounds for the ${\tau _\mu \tau _{\mathrm {h}}} $ channel. The dashed histogram shows the distribution expected for a ${\mathrm{ Z }' _{\mathrm {SSM}}}$ boson with mass 1500 GeV. The rightmost bins also include events with $ {m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )} >$ 900 GeV, and are normalized to the displayed bin width. The lower panel shows the ratio of the observed number of events to the total background prediction. The shaded bands represent the total uncertainty in the background prediction. |
png pdf |
Figure 1-d:
Observed ${m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )}$ distribution in the signal region compared to the expected SM backgrounds for the ${ {\tau _{\mathrm {h}}} {\tau _{\mathrm {h}}} }$ channel. The dashed histogram shows the distribution expected for a ${\mathrm{ Z }' _{\mathrm {SSM}}}$ boson with mass 1500 GeV. The rightmost bins also include events with $ {m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )} >$ 900 GeV, and are normalized to the displayed bin width. The lower panel shows the ratio of the observed number of events to the total background prediction. The shaded bands represent the total uncertainty in the background prediction. |
png pdf |
Figure 2:
The observed 95% CL upper limits on the product of the cross section and branching fraction into $\tau $ lepton pairs as a function of the Z' mass $m(\mathrm{ Z }' )$ (solid black lines), for the (top left) ${\tau _\mathrm{ e } \tau _\mu } $, (top right) ${\tau _\mathrm{ e } \tau _{\mathrm {h}}} $, (middle left) ${\tau _\mu \tau _{\mathrm {h}}} $, and (middle right) ${ {\tau _{\mathrm {h}}} {\tau _{\mathrm {h}}} }$ final states, and (bottom) for the combination of the four channels. The expected limits (dash-dotted lines) with one and two standard deviation (s.d.) uncertainty bands are also shown. The predictions of the NLO theory cross sections in the SSM and TAT models are represented by the red (lighter) and blue (darker) solid curves, respectively. |
png pdf |
Figure 2-a:
The observed 95% CL upper limits on the product of the cross section and branching fraction into $\tau $ lepton pairs as a function of the Z' mass $m(\mathrm{ Z }' )$ (solid black lines), for the ${\tau _\mathrm{ e } \tau _\mu } $ final state. The expected limits (dash-dotted lines) with one and two standard deviation (s.d.) uncertainty bands are also shown. The predictions of the NLO theory cross sections in the SSM and TAT models are represented by the red (lighter) and blue (darker) solid curves, respectively. |
png pdf |
Figure 2-b:
The observed 95% CL upper limits on the product of the cross section and branching fraction into $\tau $ lepton pairs as a function of the Z' mass $m(\mathrm{ Z }' )$ (solid black lines), for the ${\tau _\mathrm{ e } \tau _{\mathrm {h}}} $ final state. The expected limits (dash-dotted lines) with one and two standard deviation (s.d.) uncertainty bands are also shown. The predictions of the NLO theory cross sections in the SSM and TAT models are represented by the red (lighter) and blue (darker) solid curves, respectively. |
png pdf |
Figure 2-c:
The observed 95% CL upper limits on the product of the cross section and branching fraction into $\tau $ lepton pairs as a function of the Z' mass $m(\mathrm{ Z }' )$ (solid black lines), for the ${\tau _\mu \tau _{\mathrm {h}}} $ final state. The expected limits (dash-dotted lines) with one and two standard deviation (s.d.) uncertainty bands are also shown. The predictions of the NLO theory cross sections in the SSM and TAT models are represented by the red (lighter) and blue (darker) solid curves, respectively. |
png pdf |
Figure 2-d:
The observed 95% CL upper limits on the product of the cross section and branching fraction into $\tau $ lepton pairs as a function of the Z' mass $m(\mathrm{ Z }' )$ (solid black lines), for the ${ {\tau _{\mathrm {h}}} {\tau _{\mathrm {h}}} }$ final state. The expected limits (dash-dotted lines) with one and two standard deviation (s.d.) uncertainty bands are also shown. The predictions of the NLO theory cross sections in the SSM and TAT models are represented by the red (lighter) and blue (darker) solid curves, respectively. |
png pdf |
Figure 2-e:
The observed 95% CL upper limits on the product of the cross section and branching fraction into $\tau $ lepton pairs as a function of the Z' mass $m(\mathrm{ Z }' )$ (solid black lines), for the combination of the four channels. The expected limits (dash-dotted lines) with one and two standard deviation (s.d.) uncertainty bands are also shown. The predictions of the NLO theory cross sections in the SSM and TAT models are represented by the red (lighter) and blue (darker) solid curves, respectively. |
| Tables | |
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Table 1:
Numbers of events observed in data compared to the expected background yields and to the predicted numbers of signal events for ${\mathrm{ Z }'_{\mathrm {SSM}}}$ masses of 1.0, 1.5, and 2.0 TeV. The upper section of the table presents the inclusive yields. The lower section presents the yields after the requirement $ {m(\tau _1,\tau _2, E_{\mathrm{T}}^{\text{miss}} )} > $ 300 GeV. The uncertainties quoted in the background yields represent the combined statistical and systematic uncertainties. |
| Summary |
| A search for heavy resonances decaying to a tau lepton pair has been performed by the CMS experiment, using a data sample of proton-proton collisions at $ \sqrt{s} = $ 13 TeV collected in 2015, corresponding to an integrated luminosity of 2.2 fb$^{-1}$. The tau leptons are reconstructed in their decays to an electron (${\tau_\mathrm{ e }} $) and muon (${\tau_\mu} $), and in their hadronic decays (${\tau_{\mathrm{h}}} $). The observed invariant mass spectra in the ${\tau_\mu\tau_{\mathrm{h}}} $, ${\tau_\mathrm{ e }\tau_{\mathrm{h}}} $, ${{\tau_{\mathrm{h}}} {\tau_{\mathrm{h}}} } $, and ${\tau_\mathrm{ e }\tau_\mu} $ channels are measured and are found to be consistent with expectations from the standard model. Upper limits at 95% confidence level are derived for the product of the cross section and branching fraction for a Z' boson decaying to a tau lepton pair, as a function of the Z' mass. The presence of Z' bosons decaying to a tau lepton pair is excluded for Z' masses below 2.1 TeV in the sequential standard model. This is the first search for heavy resonances decaying to a tau lepton pair using events from proton-proton collisions at $ \sqrt{s} = $ 13 TeV, already extending previous limits [6,7,8] for this final state using the data sample collected in 2015. In the topcolor-assisted technicolor model, which predicts Z' bosons that exhibit enhanced couplings to third-generation fermions, the presence of Z' bosons decaying to a tau lepton pair is excluded for Z' masses below 1.7 TeV, resulting in the most stringent limit to date. |
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