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| CMS-SUS-18-006 ; CERN-EP-2019-154 | ||
| Search for direct pair production of supersymmetric partners to the $\tau$ lepton in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 30 July 2019 | ||
| Eur. Phys. J. C 80 (2020) 189 | ||
| Abstract: A search is presented for $\tau$ slepton pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The search is carried out in events containing two $\tau$ leptons in the final state, on the assumption that each $\tau$ slepton decays primarily to a $\tau$ lepton and a neutralino. Events are considered in which each $\tau$ lepton decays to one or more hadrons and a neutrino, or in which one of the $\tau$ leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2 fb$^{-1}$. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for $\tau$ slepton pair production in various models for $\tau$ slepton masses between 90 and 200 GeV and neutralino masses of 1, 10, and 20 GeV. In the case of purely left-handed $\tau$ slepton production and decay to a $\tau$ lepton and a neutralino with a mass of 1 GeV, the strongest limit is obtained for a $\tau$ slepton mass of 125 GeV at a factor of 1.14 larger than the theoretical cross section. | ||
| Links: e-print arXiv:1907.13179 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Diagram for direct $\tilde{\tau}$ pair production, followed by decay of each $\tilde{\tau}$ to a $\tau$ lepton and a $\tilde{\chi}^0_1$. |
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Figure 2:
Distributions in ${\Sigma {m_{\mathrm {T}}}}$ (left) and ${m_{\mathrm {T2}}}$ (right) for events in the combined 2016 and 2017 data sets passing the baseline selection in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ final state, along with the corresponding prediction for the SM background and three benchmark models for ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV, $m(\tilde{\chi}^0_1) = $ 1 GeV. The numbers within parentheses in the legend correspond to the masses of the ${\tilde{\tau} _{\mathrm {L}}}$ and $\tilde{\chi}^0_1$ in GeV. The last bin includes overflow events in each case. The shaded uncertainty bands represent the combined statistical and systematic uncertainties in the background. |
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Figure 2-a:
Distribution in ${\Sigma {m_{\mathrm {T}}}}$ for events in the combined 2016 and 2017 data sets passing the baseline selection in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ final state, along with the corresponding prediction for the SM background and three benchmark models for ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV, $m(\tilde{\chi}^0_1) = $ 1 GeV. The numbers within parentheses in the legend correspond to the masses of the ${\tilde{\tau} _{\mathrm {L}}}$ and $\tilde{\chi}^0_1$ in GeV. The last bin includes overflow events. The shaded uncertainty bands represent the combined statistical and systematic uncertainties in the background. |
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Figure 2-b:
Distribution in ${m_{\mathrm {T2}}}$ for events in the combined 2016 and 2017 data sets passing the baseline selection in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ final state, along with the corresponding prediction for the SM background and three benchmark models for ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV, $m(\tilde{\chi}^0_1) = $ 1 GeV. The numbers within parentheses in the legend correspond to the masses of the ${\tilde{\tau} _{\mathrm {L}}}$ and $\tilde{\chi}^0_1$ in GeV. The last bin includes overflow events. The shaded uncertainty bands represent the combined statistical and systematic uncertainties in the background. |
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Figure 3:
Distributions in ${{p_{\mathrm {T}}} ^\text {miss}}$ (left) and $ {m_{\mathrm {T}}} ^{\text {tot}}$ (right) for events in the combined 2016 and 2017 data passing the baseline selections in the ${\mu {\tau _\mathrm {h}}}$ final state, along with the corresponding prediction for SM background and three benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. The numbers within parentheses in the legend correspond to the masses of the ${\tilde{\tau} _{\mathrm {L}}}$ and $\tilde{\chi}^0_1$ in GeV. The last bin includes overflow events in each case. The shaded uncertainty bands represent the combined statistical and average systematic uncertainties in the background. |
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Figure 3-a:
Distribution in ${{p_{\mathrm {T}}} ^\text {miss}}$ for events in the combined 2016 and 2017 data passing the baseline selections in the ${\mu {\tau _\mathrm {h}}}$ final state, along with the corresponding prediction for SM background and three benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. The numbers within parentheses in the legend correspond to the masses of the ${\tilde{\tau} _{\mathrm {L}}}$ and $\tilde{\chi}^0_1$ in GeV. The last bin includes overflow events. The shaded uncertainty bands represent the combined statistical and average systematic uncertainties in the background. |
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Figure 3-b:
Distribution in $ {m_{\mathrm {T}}} ^{\text {tot}}$ for events in the combined 2016 and 2017 data passing the baseline selections in the ${\mu {\tau _\mathrm {h}}}$ final state, along with the corresponding prediction for SM background and three benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. The numbers within parentheses in the legend correspond to the masses of the ${\tilde{\tau} _{\mathrm {L}}}$ and $\tilde{\chi}^0_1$ in GeV. The last bin includes overflow events. The shaded uncertainty bands represent the combined statistical and average systematic uncertainties in the background. |
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Figure 4:
Visible-mass spectra of $\tau$ lepton pairs in ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ events (left) and ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution in ${\mu {\tau _\mathrm {h}}}$ events (right) in data and the corresponding prediction for SM background in the combined 2016 and 2017 DY+jets validation regions. The last bin includes overflow events in each case. The shaded uncertainty band represents the statistical and systematic uncertainties in the background prediction. For the ${\mu {\tau _\mathrm {h}}}$ distribution, the systematic uncertainty included in each bin corresponds to a single common average value. |
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Figure 4-a:
Visible-mass spectra of $\tau$ lepton pairs in ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ events in data and the corresponding prediction for SM background in the combined 2016 and 2017 DY+jets validation regions. The last bin includes overflow events in each case. The shaded uncertainty band represents the statistical and systematic uncertainties in the background prediction. |
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Figure 4-b:
${{p_{\mathrm {T}}} ^\text {miss}}$ distribution in ${\mu {\tau _\mathrm {h}}}$ events in data and the corresponding prediction for SM background in the combined 2016 and 2017 DY+jets validation regions. The last bin includes overflow events in each case. The shaded uncertainty band represents the statistical and systematic uncertainties in the background prediction. The systematic uncertainty included in each bin corresponds to a single common average value. |
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Figure 5:
Event counts and predicted yields for the SM background in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ analysis for the 2016 (left) and 2017 (right) data, before (upper) and after (lower) a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark signal models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 5-a:
Event counts and predicted yields for the SM background in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ analysis for the 2016 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark signal models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 5-b:
Event counts and predicted yields for the SM background in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ analysis for the 2017 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark signal models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 5-c:
Event counts and predicted yields for the SM background in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ analysis for the 2016 data, after a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark signal models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 5-d:
Event counts and predicted yields for the SM background in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ analysis for the 2017 data, after a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark signal models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 6:
Discriminant distributions for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mu {\tau _\mathrm {h}}}$ final state for the 2016 (left) and 2017 (right) data, before (upper) and after (lower) a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 6-a:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mu {\tau _\mathrm {h}}}$ final state for the 2016 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 6-b:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mu {\tau _\mathrm {h}}}$ final state for the 2017 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 6-c:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mu {\tau _\mathrm {h}}}$ final state for the 2016 data, after a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 6-d:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mu {\tau _\mathrm {h}}}$ final state for the 2017 data, after a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 7:
Discriminant distributions for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mathrm{e} {\tau _\mathrm {h}}}$ final state for the 2016 (left) and 2017 (right) data, before (upper) and after (lower) a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 7-a:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mathrm{e} {\tau _\mathrm {h}}}$ final state for the 2016 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 7-b:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mathrm{e} {\tau _\mathrm {h}}}$ final state for the 2017 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 7-c:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mathrm{e} {\tau _\mathrm {h}}}$ final state for the 2016 data, before a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 7-d:
Discriminant distribution for the BDT trained for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV (BDT (100)) in the ${\mathrm{e} {\tau _\mathrm {h}}}$ final state for the 2017 data, after a maximum-likelihood fit to the data. Predicted signal yields are also shown for benchmark models of ${\tilde{\tau} _{\mathrm {L}}}$ pair production with $m({\tilde{\tau} _{\mathrm {L}}})=$ 100, 125, and 200 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. |
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Figure 8:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the purely left-handed $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 1 GeV (upper left), 10 GeV (upper right) and 20 GeV (lower). The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
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Figure 8-a:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the purely left-handed $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 1 GeV. The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
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Figure 8-b:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the purely left-handed $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 10 GeV. The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
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Figure 8-c:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the purely left-handed $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 20 GeV. The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
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Figure 9:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the degenerate $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 1 GeV (upper left), 10 GeV (upper right) and 20 GeV (lower). The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
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Figure 9-a:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the degenerate $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 1 GeV. The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
png pdf |
Figure 9-b:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the degenerate $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 10 GeV. The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
png pdf |
Figure 9-c:
Upper limit on the cross section ($\sigma $) of $\tilde{\tau}$ pair production excluded at 95% CL as a function of the $\tilde{\tau}$ mass in the degenerate $\tilde{\tau}$ models for a $\tilde{\chi}^0_1$ mass of 20 GeV. The results shown are for the statistical combination of the 2016 and 2017 data in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ and ${\ell {\tau _\mathrm {h}}}$ analyses. The inner (green) and outer (yellow) bands indicate the respective regions containing 68 and 95% of the distribution of limits expected under the background-only hypothesis. The solid red line indicates the NLO+NLL prediction for the signal production cross section calculated with Resummino [39], while the red shaded band represents the uncertainty in the prediction. |
| Tables | |
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Table 1:
Ranges in ${m_{\mathrm {T2}}}$, ${\Sigma {m_{\mathrm {T}}}}$, and ${N_{\text {j}}}$ used to define the SRs used in the ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ analysis. |
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Table 2:
Systematic uncertainties of SM background predictions and a representative signal model, corresponding to a left-handed $\tilde{\tau}$, with $m(\tilde{\tau}) = $ 100 GeV and $m(\tilde{\chi}^0_1) = $ 1 GeV. The uncertainty ranges are given in percent. The spread of values reflects uncertainties in different SRs. |
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Table 3:
Predicted background yields and observed event counts in ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ SRs in 2016 data. For the background estimates with no events in the sideband or in the simulated sample, we calculate the 68% CL upper limit on the yield. The first and second uncertainties given are statistical and systematic, respectively. We also list the predicted signal yields corresponding to the purely left-handed model for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV. |
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Table 4:
Predicted background yields and observed event counts in ${{\tau _\mathrm {h}} {\tau _\mathrm {h}}}$ SRs in 2017 data. For the background estimates with no events in the sideband or in the simulated sample, we calculate the 68% CL upper limit on the yield. The first and second uncertainties given are statistical and systematic, respectively. We also list the predicted signal yields corresponding to the purely left-handed model for a $\tilde{\tau}$ mass of 100 GeV and a $\tilde{\chi}^0_1$ mass of 1 GeV. |
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Table 5:
Predicted background yields and observed event counts in the most sensitive last bins of the BDT distributions in the ${\mathrm{e} {\tau _\mathrm {h}}}$ and ${\mu {\tau _\mathrm {h}}}$ final states, in data collected in 2016. The numbers in parentheses in the first row are the $\tilde{\tau}$ and $\tilde{\chi}^0_1$ masses corresponding to the signal model for left-handed $\tilde{\tau}$ pair production that is used to train the BDT. In the bottom row, we list the corresponding predicted signal yields in the last bin of the BDT distribution. The first and second uncertainties given are statistical and systematic, respectively. |
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Table 6:
Predicted background yields and observed event counts in the most sensitive last bins of the BDT distributions in the ${\mathrm{e} {\tau _\mathrm {h}}}$ and ${\mu {\tau _\mathrm {h}}}$ final states, in data collected in 2017. The numbers in parentheses in the first row are the $\tilde{\tau}$ and $\tilde{\chi}^0_1$ masses corresponding to the signal model for left-handed $\tilde{\tau}$ pair production that is used to train the BDT. In the bottom row, we list the corresponding predicted signal yields in the last bin of the BDT distribution. The first and second uncertainties given are statistical and systematic, respectively. |
| Summary |
| A search for direct $\tau$ slepton ($\tilde{\tau}$) pair production has been performed in proton-proton collisions at a center-of-mass energy of 13 TeV in events with a $\tau$ lepton pair and significant missing transverse momentum. Search regions are defined using kinematic observables that exploit expected differences in discriminants between signal and background. The data used for this search correspond to an integrated luminosity of 77.2 fb$^{-1}$ collected in 2016 and 2017 with the CMS detector. No excess above the expected standard model background has been observed. Upper limits have been set on the cross section for direct $\tilde{\tau}$ pair production for simplified models in which each $\tilde{\tau}$ decays to a $\tau$ lepton and the lightest neutralino, with the latter being assumed to be the lightest supersymmetric particle. For purely left-handed $\tilde{\tau}$ pair production, the analysis is most sensitive to a $\tilde{\tau}$ mass of 125 GeV when the neutralino is nearly massless. The observed limit is a factor of 1.14 larger than the expected production cross section in this model. The limits observed for left-handed $\tilde{\tau}$ pair production are the strongest obtained thus far for low values of the $\tilde{\tau}$ mass. In a more optimistic, degenerate production model, in which both left- and right-handed $\tilde{\tau}$ pairs are produced, we exclude $\tilde{\tau}$ masses up to 150 GeV, again under the assumption of a nearly massless neutralino. These results represent the first exclusion reported for this model for low values of the $\tilde{\tau}$ mass between 90 and 120 GeV. |
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