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| CMS-EXO-17-009 ; CERN-EP-2018-265 | ||
| Search for pair production of first-generation scalar leptoquarks at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 3 November 2018 | ||
| Phys. Rev. D 99 (2019) 052002 | ||
| 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 LHC. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$. The leptoquarks are assumed to decay promptly to a quark and either an electron or a neutrino, with branching fractions $\beta$ and $ 1{-}\beta $, respectively. The search targets the decay final states comprising two electrons, or one electron and large missing transverse momentum, along with two quarks that are detected as hadronic jets. First-generation scalar leptoquarks with masses below 1435 (1270) GeV are excluded for $\beta =$ 1.0 (0.5). These are the most stringent limits on the mass of first-generation scalar leptoquarks to date. The data are also interpreted to set exclusion limits in the context of an $R$-parity violating supersymmetric model, predicting promptly decaying top squarks with a similar dielectron final state. | ||
| Links: e-print arXiv:1811.01197 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading order Feynman diagrams for the scalar LQ pair production channels at the LHC. |
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Figure 1-a:
Leading order Feynman diagram for the scalar LQ pair production at the LHC. |
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Figure 1-b:
Leading order Feynman diagram for the scalar LQ pair production at the LHC. |
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Figure 1-c:
Leading order Feynman diagram for the scalar LQ pair production at the LHC. |
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Figure 1-d:
Leading order Feynman diagram for the scalar LQ pair production at the LHC. |
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Figure 2:
Optimized threshold values applied for the selection variables in the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) channels as a function of $ {m_{\text {LQ}}} $. |
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Figure 2-a:
Optimized threshold values applied for the selection variables in the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel as a function of $ {m_{\text {LQ}}} $. |
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Figure 2-b:
Optimized threshold values applied for the selection variables in the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel as a function of $ {m_{\text {LQ}}} $. |
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Figure 3:
Data and background comparison for events passing the initial selection requirements for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel, shown for the variables used for final selection optimization: $ {m_{{\mathrm {e}} {\mathrm {e}}}} $ (upper), $ {m_{{\mathrm {e}}\text {j}}^\text {min}} $ (lower left), and $ {S_{\mathrm {T}}} $ (lower right). "Other background" includes diboson, single top quark, and W+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plots. 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 the initial selection requirements for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel, shown for the $ {m_{{\mathrm {e}} {\mathrm {e}}}} $ variable. "Other background" includes diboson, single top quark, and W+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. 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 the initial selection requirements for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel, shown for the $ {m_{{\mathrm {e}}\text {j}}^\text {min}} $ variable. "Other background" includes diboson, single top quark, and W+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. 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 the initial selection requirements for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel, shown for the $ {S_{\mathrm {T}}} $ variable. "Other background" includes diboson, single top quark, and W+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 4:
Data and background for events passing the initial selection requirements in the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel, shown for the variables used for final selection optimization: $ {m_{\mathrm {T}}} $ (upper left), $ {m_{{\mathrm {e}}\text {j}}} $ (upper right), $ {S_{\mathrm {T}}} $ (lower left), and $ {{p_{\mathrm {T}}} ^\text {miss}} $ (lower right). "Other background" includes diboson, single top quark, and Z/$\gamma^{*}$+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plots. 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 the initial selection requirements in the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel, shown for the $ {m_{\mathrm {T}}} $ variable. "Other background" includes diboson, single top quark, and Z/$\gamma^{*}$+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. 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 the initial selection requirements in the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel, shown for the $ {m_{{\mathrm {e}}\text {j}}} $ variable. "Other background" includes diboson, single top quark, and Z/$\gamma^{*}$+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. 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 the initial selection requirements in the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel, shown for the $ {S_{\mathrm {T}}} $ variable. "Other background" includes diboson, single top quark, and Z/$\gamma^{*}$+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. 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 the initial selection requirements in the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel, shown for the $ {{p_{\mathrm {T}}} ^\text {miss}} $ variable. "Other background" includes diboson, single top quark, and Z/$\gamma^{*}$+jets. Signal predictions for $ {m_{\text {LQ}}} = $ 650 and 1200 GeV hypotheses are overlaid on the plot. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 5:
$ {m_{{\mathrm {e}}\text {j}}^\text {min}} $ (left) and $ {S_{\mathrm {T}}} $ (right) distributions for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for LQs of mass 650 (upper) and 1200 (lower) GeV. 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 $\gamma$+jets contributions. The background contributions are stacked, while the signal distributions are plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 5-a:
$ {m_{{\mathrm {e}}\text {j}}^\text {min}} $ distribution for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for LQs of mass 650 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 5-b:
$ {S_{\mathrm {T}}} $ distribution for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for LQs of mass 650 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 5-c:
$ {m_{{\mathrm {e}}\text {j}}^\text {min}} $ distribution for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for LQs of mass 1200 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 5-d:
$ {S_{\mathrm {T}}} $ distribution for events passing the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ final selection for LQs of mass 1200 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of the W+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 6:
$ {m_{{\mathrm {e}}\text {j}}} $ (left) and $ {S_{\mathrm {T}}} $ (right) distributions for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for LQs of mass 650 (upper) and 1200 (lower) GeV. The predicted signal model distributions are shown, along with major backgrounds and "other background'' which consists of the sum of Z/$\gamma^{*}$+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distributions are plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 6-a:
$ {m_{{\mathrm {e}}\text {j}}} $ distribution for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for LQs of mass 650 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of Z/$\gamma^{*}$+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 6-b:
$ {S_{\mathrm {T}}} $ distribution for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for LQs of mass 650 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of Z/$\gamma^{*}$+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 6-c:
$ {m_{{\mathrm {e}}\text {j}}} $ distribution for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for LQs of mass 1200 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of Z/$\gamma^{*}$+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total background. The last bin includes all events beyond the upper $x$-axis boundary. |
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Figure 6-d:
$ {S_{\mathrm {T}}} $ distribution for events passing the $ {{\mathrm {e}} {\nu}\text {jj}} $ final selection for LQs of mass 1200 GeV. The predicted signal model distribution is shown, along with major backgrounds and "other background'' which consists of the sum of Z/$\gamma^{*}$+jets, diboson, single top quark, and $\gamma$+jets contributions. The background contributions are stacked, while the signal distribution is plotted unstacked. The dark shaded region indicates the statistical and systematic uncertainty in the total 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 selection criteria for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) channels. "Other background" includes diboson, single top quark, and W+jets (for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel) or Z/$\gamma^{*}$+jets (for the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel). The bin contents are correlated, because events selected for higher-mass LQ searches are a subset of those selected for lower mass searches. |
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Figure 7-a:
Data, background, and expected signal yields after applying the final selection criteria for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel. "Other background" includes diboson, single top quark, and W+jets (for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel) or Z/$\gamma^{*}$+jets (for the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel). The bin contents are correlated, because events selected for higher-mass LQ searches are a subset of those selected for lower mass searches. |
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Figure 7-b:
Data, background, and expected signal yields after applying the final selection criteria for the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel. "Other background" includes diboson, single top quark, and W+jets (for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel) or Z/$\gamma^{*}$+jets (for the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel). The bin contents are correlated, because events selected for higher-mass LQ searches are a subset of those selected for lower mass searches. |
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Figure 8:
Observed upper limits for scalar LQ pair-production cross section times $\beta ^2$ (left) and $\beta (1{-}\beta)$ (right) at 95% CL obtained with the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) analysis. The median (dashed line), 68% (inner green band) and 95% (outer yellow band) confidence-interval expected limits are also shown. |
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Figure 8-a:
Observed upper limits for scalar LQ pair-production cross section times $\beta ^2$ at 95% CL obtained with the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ analysis. The median (dashed line), 68% (inner green band) and 95% (outer yellow band) confidence-interval expected limits are also shown. |
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Figure 8-b:
Observed upper limits for scalar LQ pair-production cross section times $\beta (1{-}\beta)$ at 95% CL obtained with the $ {{\mathrm {e}} {\nu}\text {jj}} $ analysis. The median (dashed line), 68% (inner green band) and 95% (outer yellow band) confidence-interval expected limits are also shown. |
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Figure 9:
Expected and observed exclusion limits at 95% CL for pair production of first-generation scalar LQ shown in the $\beta $ versus $ {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 green and outer yellow bands represent the 68% and 95% confidence intervals on the expected limits. |
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Figure 10:
Expected and observed upper limits at 95% CL on the RPV SUSY $ {\tilde{\mathrm {t}}} $ squark pair production cross section as a function of $M_{{\tilde{\mathrm {t}}}}$ for $c\tau =$ 0 cm. The expected limits represent the median values, while the inner green and outer yellow bands are the 68% and 95% confidence intervals, respectively. |
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Figure 11:
The product of signal acceptance and efficiency after final optimized selections, as a function of $ {m_{\text {LQ}}} $ for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ (left) and $ {{\mathrm {e}} {\nu}\text {jj}} $ (right) channels. |
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Figure 11-a:
The product of signal acceptance and efficiency after final optimized selections, as a function of $ {m_{\text {LQ}}} $ for the $ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $ channel. |
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Figure 11-b:
The product of signal acceptance and efficiency after final optimized selections, as a function of $ {m_{\text {LQ}}} $ for the $ {{\mathrm {e}} {\nu}\text {jj}} $ channel. |
| 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 the event yields due to each source. Major backgrounds, namely Z/$\gamma^{*}$+jets \ ($ {{\mathrm {e}} {\mathrm {e}}\text {jj}} $), W+jets and $ {{\mathrm {t}\overline {\mathrm {t}}}} $ ($ {{\mathrm {e}} {\nu}\text {jj}} $), are normalized at the initial selection level when calculating the effect of shifts for various systematics. |
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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. An entry of 0.0 quoted for the uncertainty indicates that its value is negligibly small. LQ masses are given in units of GeV and init. sel. refers to initial selection. |
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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. An entry of 0.0 quoted for the uncertainty indicates that its value is negligibly small. LQ masses are given in units of GeV and init. sel. refers to initial selection. |
| Summary |
| A search has been performed for the pair production of first-generation scalar leptoquarks in final states consisting of two high-momentum electrons and two jets, or 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 standard model background expectations and a lower limit at 95% confidence level is set on the scalar leptoquark mass at 1435 (1270) GeV for $\beta=$ 1.0 (0.5), where $\beta$ is the branching fraction of the leptoquark decay to an electron and a quark. These results constitute the most stringent limits on the mass of first-generation scalar leptoquarks to date. The data are also interpreted in the context of an $R$-parity violating supersymmetric model with promptly decaying top squarks, which can decay into leptoquark-like final states. Top squarks are excluded for masses below 1100 GeV. |
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