CMS-PAS-SUS-17-003 | ||
Search for pair production of tau sleptons in $\sqrt{s}= $ 13 TeV pp collisions in the all-hadronic final state | ||
CMS Collaboration | ||
July 2017 | ||
Abstract: A search for direct tau slepton pair production in pp collisions at a center-of-mass energy of 13 TeV is presented. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected with the CMS detector at the Run-2 of the CERN LHC in 2016. The search is performed using events with two hadronically decaying tau leptons and a large imbalance in the measured transverse momentum of the event. The results are interpreted as upper limits on the cross section for tau slepton pair production in different helicity scenarios. | ||
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These preliminary results are superseded in this paper, JHEP 11 (2018) 151. The superseded preliminary plots can be found here. |
Figures & Tables | Summary | Additional Figures & Tables | References | CMS Publications |
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Additional information on efficiencies needed for reinterpretation of these results are available here. Additional technical material for CMS speakers can be found here. |
Figures | |
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Figure 1:
Simplified model for direct stau pair production followed by each stau decaying to a $\tau $ lepton and an LSP. |
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Figure 2:
The $\Sigma {M_{\mathrm {T}}} $ (left) and $ {M_{\mathrm {T2}}} $ (right) distributions after the baseline selection. The signatures of stau pair production with different stau masses are shown. A requirement of large $ {M_{\mathrm {T2}}} $, while efficient at reducing the SM background, greatly reduces the signal acceptance for low stau masses. We therefore define additional search regions with moderate $ {M_{\mathrm {T2}}} $ and use $\Sigma {M_{\mathrm {T}}} $ as a discriminating variable to target smaller stau masses. Three signal hypotheses in the maximally-mixed scenario are overlaid, with the first number indicating the stau mass and the second the LSP mass. |
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Figure 2-a:
The $\Sigma {M_{\mathrm {T}}} $ distribution after the baseline selection. The signatures of stau pair production with different stau masses are shown. A requirement of large $ {M_{\mathrm {T2}}} $, while efficient at reducing the SM background, greatly reduces the signal acceptance for low stau masses. We therefore define additional search regions with moderate $ {M_{\mathrm {T2}}} $ and use $\Sigma {M_{\mathrm {T}}} $ as a discriminating variable to target smaller stau masses. Three signal hypotheses in the maximally-mixed scenario are overlaid, with the first number indicating the stau mass and the second the LSP mass. |
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Figure 2-b:
The $ {M_{\mathrm {T2}}} $ distribution after the baseline selection. The signatures of stau pair production with different stau masses are shown. A requirement of large $ {M_{\mathrm {T2}}} $, while efficient at reducing the SM background, greatly reduces the signal acceptance for low stau masses. We therefore define additional search regions with moderate $ {M_{\mathrm {T2}}} $ and use $\Sigma {M_{\mathrm {T}}} $ as a discriminating variable to target smaller stau masses. Three signal hypotheses in the maximally-mixed scenario are overlaid, with the first number indicating the stau mass and the second the LSP mass. |
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Figure 3:
(Left) Closure test for the fake rate method in a data control region where the $ {M_{\mathrm {T2}}} $ or $\Sigma {M_{\mathrm {T}}} $ requirements are inverted. The predicted and observed yields show good agreement. (Right) The visible mass spectrum is used to validate our modeling of Drell-Yan backgrounds. A minimum di-$ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ of 50 GeV is required to reduce the QCD multijet background. Data and simulation agree within the experimental uncertainties. |
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Figure 3-a:
Closure test for the fake rate method in a data control region where the $ {M_{\mathrm {T2}}} $ or $\Sigma {M_{\mathrm {T}}} $ requirements are inverted. The predicted and observed yields show good agreement. |
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Figure 3-b:
The visible mass spectrum is used to validate our modeling of Drell-Yan backgrounds. A minimum di-$ {\tau _\mathrm {h}} $ ${p_{\mathrm {T}}}$ of 50 GeV is required to reduce the QCD multijet background. Data and simulation agree within the experimental uncertainties. |
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Figure 4:
The excluded stau pair production cross section as a function of the stau mass for the three different helicities: left-handed (left), maximally-mixed (middle), right-handed (right). The plots in the top row assume a fixed LSP mass of 1 GeV, the ones on the middle row 20 GeV, and the ones on the bottom row 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-a:
The excluded stau pair production cross section as a function of the stau mass for left-handed helicity. The plot assumes a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-b:
The excluded stau pair production cross section as a function of the stau mass for maximally-mixed helicity. The plot assumes a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-c:
The excluded stau pair production cross section as a function of the stau mass for right-handed helicity. The plot assumes a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-d:
The excluded stau pair production cross section as a function of the stau mass for left-handed helicity. The plot assumes a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-e:
The excluded stau pair production cross section as a function of the stau mass for maximally-mixed helicity. The plot assumes a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-f:
The excluded stau pair production cross section as a function of the stau mass for right-handed helicity. The plot assumes a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-g:
The excluded stau pair production cross section as a function of the stau mass for left-handed helicity. The plot assumes a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-h:
The excluded stau pair production cross section as a function of the stau mass for maximally-mixed helicity. The plot assumes a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
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Figure 4-i:
The excluded stau pair production cross section as a function of the stau mass for right-handed helicity. The plot assumes a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
Tables | |
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Table 1:
The largest systematic uncertainties in the analysis for the signal models and the different SM background predictions. For the signal models the uncertainties are re-evaluated for the different mass hypotheses. |
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Table 2:
Final predicted and observed event yields in all SRs with all statistical and systematic uncertainties combined. For the background estimates with no events in the sideband or the simulated sample, the 68% statistical upper limit is presented. For the total background estimate the central value and the uncertainties are extracted from the full pre-fit likelihood. |
Summary |
A search for tau sleptons in the all-hadronic final state was performed in pp collisions at a center-of-mass energy of 13 TeV using three complementary search regions. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$. No excess was observed in any of the search regions. Upper limits on the cross section of direct tau slepton (stau) pair production are derived, for each stau decaying to a tau lepton and an LSP. The analysis is most sensitive to left-handed staus. For a left-handed stau of 125 GeV decaying to a massless LSP the observed limit is 1.5 times the expected production cross section in the simplified model. |
Additional Figures | |
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Additional Figure 1:
Misidentification rate as a function of $\tau$ $p_{\mathrm {T}}$ for various parton types without any cut on the isolation (left) or after applying a loose isolation requirement as done in the analysis (right). The variation across parton types is greatly reduced by applying such a requirement. After applying the loose isolation requirement, a systematic uncertainty of 30% is assigned to the misidentification rate to cover the jet parton dependence as this analysis does not determine the jet parton type. |
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Additional Figure 1-a:
Misidentification rate as a function of $\tau$ $p_{\mathrm {T}}$ for various parton types without any cut on the isolation. The variation across parton types is greatly reduced by applying such a requirement. |
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Additional Figure 1-b:
Misidentification rate as a function of $\tau$ $p_{\mathrm {T}}$ for various parton types after applying a loose isolation requirement as done in the analysis. The variation across parton types is greatly reduced by applying such a requirement. After applying the loose isolation requirement, a systematic uncertainty of 30% is assigned to the misidentification rate to cover the jet parton dependence as this analysis does not determine the jet parton type. |
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Additional Figure 2:
Illustration showing the complementarity of the different search and control regions. |
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Additional Figure 3:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 1 GeV (left), 20 GeV (middle), and 50 GeV (right). The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model. |
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Additional Figure 3-a:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 1 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model. |
png pdf |
Additional Figure 3-b:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 20 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model. |
png pdf |
Additional Figure 3-c:
The excluded cross sections for stau pair production as a function of the stau mass for a model where the left-handed and right-handed staus are considered to be mass degenerate. The plots are shown for a fixed LSP mass of 50 GeV. The inner (green) band and the outer (yellow) band indicate the regions containing 68% (1 s.d.) and 95% (2 s.d.), respectively, of the distribution of limits expected under the background-only hypothesis. Several mass hypotheses are just excluded in this model. |
Additional Tables | |
png pdf |
Additional Table 1:
Cut-flow for different mass points of the left-handed stau sample for all three search regions corresponding to 35.9 fb$^{-1}$ of integrated luminosity for various signal model points, given as the mass pair ($\tilde{\tau }$,$\tilde{\chi }_1^{0}$). The yields are normalized to the theoretical cross sections. The baseline selection requires exactly two hadronic tau candidates passing the kinematic and trigger requirements and no additional electrons or muons. |
References | ||||
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Compact Muon Solenoid LHC, CERN |