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| CMS-PAS-EXO-17-009 | ||
| Search for pair production of first generation scalar leptoquarks at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| July 2018 | ||
| Abstract: A search for the pair production of first generation scalar leptoquarks is performed using proton-proton collision data recorded at 13 TeV center-of-mass energy with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$. The leptoquarks are assumed to decay to either an electron or a neutrino and a quark with branching fraction $\beta$ and $ 1-\beta $, respectively. The final states arising from these decays comprise two electrons, or one electron and large missing transverse momentum, and two quarks that are detected as hadronic jets. First generation scalar leptoquarks with masses below 1435 (1180) TeV are excluded for $\beta = $ 1.0 (0.5). These are the most stringent limits on the production of first generation scalar leptoquarks to date. The data are also interpreted to set exclusion limits in the context of a long-lived R-parity violating supersymmetry model having equivalent final states. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRD 99 (2019) 052002. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Feynman diagrams for the dominant scalar leptoquark pair production channels at the LHC. |
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Figure 1-a:
Feynman diagrams for the dominant scalar leptoquark pair production channels at the LHC. |
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Figure 1-b:
Feynman diagrams for the dominant scalar leptoquark pair production channels at the LHC. |
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Figure 1-c:
Feynman diagrams for the dominant scalar leptoquark pair production channels at the LHC. |
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Figure 1-d:
Feynman diagrams for the dominant scalar leptoquark pair production channels at the LHC. |
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Figure 2:
Final selection thresholds for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) channels as a function of LQ mass. |
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Figure 2-a:
Final selection thresholds for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) channels as a function of LQ mass. |
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Figure 2-b:
Final selection thresholds for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) channels as a function of LQ mass. |
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Figure 3:
Data and background comparison for events passing initial selection requirements for the ${{\mathrm {e}} {\mathrm {e}}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${\text M_{{\mathrm {e}} {\mathrm {e}}}}$ (top), ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (bottom left), and ${{\text S}_{\mathrm {T}}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 3-a:
Data and background comparison for events passing initial selection requirements for the ${{\mathrm {e}} {\mathrm {e}}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${\text M_{{\mathrm {e}} {\mathrm {e}}}}$ (top), ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (bottom left), and ${{\text S}_{\mathrm {T}}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 3-b:
Data and background comparison for events passing initial selection requirements for the ${{\mathrm {e}} {\mathrm {e}}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${\text M_{{\mathrm {e}} {\mathrm {e}}}}$ (top), ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (bottom left), and ${{\text S}_{\mathrm {T}}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 3-c:
Data and background comparison for events passing initial selection requirements for the ${{\mathrm {e}} {\mathrm {e}}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${\text M_{{\mathrm {e}} {\mathrm {e}}}}$ (top), ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (bottom left), and ${{\text S}_{\mathrm {T}}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 4:
Data and background for events passing initial selection requirements in the ${{\mathrm {e}} {\nu}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${{\text M}_{\mathrm {T}}}$ (top right), ${{\text M}_{{\mathrm {e}}\text {j}}}$ (top left), ${{\text S}_{\mathrm {T}}}$ (bottom left), and ${{p_{\mathrm {T}}} ^\text {miss}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 4-a:
Data and background for events passing initial selection requirements in the ${{\mathrm {e}} {\nu}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${{\text M}_{\mathrm {T}}}$ (top right), ${{\text M}_{{\mathrm {e}}\text {j}}}$ (top left), ${{\text S}_{\mathrm {T}}}$ (bottom left), and ${{p_{\mathrm {T}}} ^\text {miss}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 4-b:
Data and background for events passing initial selection requirements in the ${{\mathrm {e}} {\nu}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${{\text M}_{\mathrm {T}}}$ (top right), ${{\text M}_{{\mathrm {e}}\text {j}}}$ (top left), ${{\text S}_{\mathrm {T}}}$ (bottom left), and ${{p_{\mathrm {T}}} ^\text {miss}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 4-c:
Data and background for events passing initial selection requirements in the ${{\mathrm {e}} {\nu}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${{\text M}_{\mathrm {T}}}$ (top right), ${{\text M}_{{\mathrm {e}}\text {j}}}$ (top left), ${{\text S}_{\mathrm {T}}}$ (bottom left), and ${{p_{\mathrm {T}}} ^\text {miss}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 4-d:
Data and background for events passing initial selection requirements in the ${{\mathrm {e}} {\nu}\text {jj}}$ channel, shown for the variables used for final selection optimization: ${{\text M}_{\mathrm {T}}}$ (top right), ${{\text M}_{{\mathrm {e}}\text {j}}}$ (top left), ${{\text S}_{\mathrm {T}}}$ (bottom left), and ${{p_{\mathrm {T}}} ^\text {miss}}$ (bottom right). The last bin includes all events beyond the upper x-axis boundary. |
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Figure 5:
The ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (left) and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and photon+jets contributions. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 5-a:
The ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (left) and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and photon+jets contributions. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 5-b:
The ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (left) and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and photon+jets contributions. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 5-c:
The ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (left) and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and photon+jets contributions. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 5-d:
The ${{\text M}_{{\mathrm {e}}\text {j}}^\mathrm {min}}$ (left) and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and photon+jets contributions. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 6:
The ${{\text M}_{{\mathrm {e}}\text {j}}}$ (left), and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the Z/$\gamma$+jets, diboson, single top quark, and photon+jets backgrounds. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 6-a:
The ${{\text M}_{{\mathrm {e}}\text {j}}}$ (left), and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the Z/$\gamma$+jets, diboson, single top quark, and photon+jets backgrounds. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
png pdf |
Figure 6-b:
The ${{\text M}_{{\mathrm {e}}\text {j}}}$ (left), and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the Z/$\gamma$+jets, diboson, single top quark, and photon+jets backgrounds. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
png pdf |
Figure 6-c:
The ${{\text M}_{{\mathrm {e}}\text {j}}}$ (left), and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the Z/$\gamma$+jets, diboson, single top quark, and photon+jets backgrounds. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
png pdf |
Figure 6-d:
The ${{\text M}_{{\mathrm {e}}\text {j}}}$ (left), and ${{\text S}_{\mathrm {T}}}$ (right) distributions for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for leptoquarks of mass 650 GeV (top) and 1200 GeV (bottom). The predicted signal model distributions are shown, along with major backgrounds, and "other background'' which consists of the sum of the Z/$\gamma$+jets, diboson, single top quark, and photon+jets backgrounds. The dark shaded region indicates the statistical and systematic uncertainty on the total predicted background. The last bin includes all events beyond the upper x-axis boundary. |
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Figure 7:
Data, background, and expected signal yields after applying the final $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ selection criteria as a function of LQ mass. 'Other background' includes diboson, single top quark, and W+jets. The bins are correlated, because events selected for higher LQ searches are a subset of those selected for lower mass searches. |
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Figure 8:
Data, background, and signal yields after applying the final $ {{\mathrm {e}} {\nu}\text {jj}} $ selection criteria as a function of LQ mass. 'Other background' includes diboson, single top quark, and Z/$\gamma$+jets. The bins are correlated, because events selected for higher LQ searches are a subset of those selected for lower mass searches. |
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Figure 9:
Observed upper limits for scalar leptoquark pair-production cross section times $\beta ^2$ (left plot) and $\beta (1-\beta)$ (right plot) at the 95% confidence level obtained with the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left plot) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right plot) analysis. The median (dashed line), 1$\sigma $ (inner band), and 2$\sigma $ (outer band) expected limits are also shown. |
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Figure 9-a:
Observed upper limits for scalar leptoquark pair-production cross section times $\beta ^2$ (left plot) and $\beta (1-\beta)$ (right plot) at the 95% confidence level obtained with the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left plot) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right plot) analysis. The median (dashed line), 1$\sigma $ (inner band), and 2$\sigma $ (outer band) expected limits are also shown. |
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Figure 9-b:
Observed upper limits for scalar leptoquark pair-production cross section times $\beta ^2$ (left plot) and $\beta (1-\beta)$ (right plot) at the 95% confidence level obtained with the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left plot) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right plot) analysis. The median (dashed line), 1$\sigma $ (inner band), and 2$\sigma $ (outer band) expected limits are also shown. |
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Figure 10:
Expected and observed exclusion limits at 95% CL for pair production of first generation scalar leptoquarks shown in the $\beta $ versus $ {{\text M}_{\text {LQ}}} $ plane for the individual $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ and $ {{\mathrm {e}} {\nu}\text {jj}} $ channels and their combination. The inner and outer uncertainty bands represent the 68% and 95% confidence intervals on the expected limits. |
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Figure 11:
Expected and observed upper limits at 95% CL on the long-lived RPV SUSY $ \mathrm{ t \bar{t} } $ pair production cross section as a function of $ \mathrm{ t \bar{t} } $ mass for $c\tau =$ 0.1 cm (left) and 1 cm (right). The expected limits represent the median values while the uncertainty bands are the 68% and 95% confidence intervals. |
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Figure 11-a:
Expected and observed upper limits at 95% CL on the long-lived RPV SUSY $ \mathrm{ t \bar{t} } $ pair production cross section as a function of $ \mathrm{ t \bar{t} } $ mass for $c\tau =$ 0.1 cm (left) and 1 cm (right). The expected limits represent the median values while the uncertainty bands are the 68% and 95% confidence intervals. |
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Figure 11-b:
Expected and observed upper limits at 95% CL on the long-lived RPV SUSY $ \mathrm{ t \bar{t} } $ pair production cross section as a function of $ \mathrm{ t \bar{t} } $ mass for $c\tau =$ 0.1 cm (left) and 1 cm (right). The expected limits represent the median values while the uncertainty bands are the 68% and 95% confidence intervals. |
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Figure 12:
Expected and observed upper limits at 95% CL on the long-lived RPV SUSY $\tilde{ \mathrm{t} }$ pair production cross section as a function of $\tilde{ \mathrm{t} }$ mass (x-axis) and lifetime (y-axis). The expected limits and uncertainty bands represent the median expected limits and the 68% and 95% confidence intervals. |
| Tables | |
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Table 1:
Systematic uncertainties for the ${{\mathrm {e}} {\mathrm {e}}\text {jj}}$ and ${{\mathrm {e}} {\nu}\text {jj}}$ channels. The values shown are calculated for the selections used in the $M_{\text LQ}= $ 1000 GeV search hypothesis and reflect the variations in event yields due to each source. |
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Table 2:
Event yields after the optimized $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ selections. Uncertainties are statistical except for the total background, where both statistical and systematic uncertainties are shown. LQ masses are in GeV. |
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Table 3:
Event yields after the optimized $ {{\mathrm {e}} {\nu}\text {jj}} $ selections. Uncertainties are statistical except for the total background, where both statistical and systematic uncertainties are shown. LQ masses are in GeV. |
| Summary |
| A search has been performed for pair-produced first generation scalar leptoquarks in final states consisting of two high-momentum electrons and two jets, as well as one electron, large missing transverse momentum and two jets. The data sample used in the study corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS experiment at $\sqrt{s}=13$ TeV. The data are found to be in agreement with SM background expectations and a 95% confidence level lower limit is set on the scalar leptoquark mass at 1435 (1196) GeV for $\beta= $ 1.0 (0.5), where $\beta$ is the branching fraction of the leptoquark decay to an electron and a quark. These constitute the most stringent limits on first generation scalar leptoquark production to date. The data are also interpreted in the context of a long-lived R-parity violating supersymmetry model, where the squarks can decay into leptoquark-like final states. Top squarks with lifetime $c\tau = $ 0.1 (1.0) cm are excluded for masses below 800 (270) GeV. |
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