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| CMS-EXO-19-021 ; CERN-EP-2020-202 | ||
| Search for long-lived particles using displaced jets in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 2 December 2020 | ||
| Phys. Rev. D 104 (2021) 012015 | ||
| Abstract: An inclusive search is presented for long-lived particles using displaced jets. The search uses a data sample collected with the CMS detector at the CERN LHC in 2017 and 2018, from proton-proton collisions at a center-of-mass energy of 13 TeV. The results of this search are combined with those of a previous search using a data sample collected with the CMS detector in 2016, yielding a total integrated luminosity of 132 fb$^{-1}$. The analysis searches for the distinctive topology of displaced tracks and displaced vertices associated with a dijet system. For a simplified model, where pair-produced long-lived neutral particles decay into quark-antiquark pairs, pair production cross sections larger than 0.07 fb are excluded at 95% confidence level (CL) for long-lived particle masses larger than 500 GeV and mean proper decay lengths between 2 and 250 mm. For a model where the standard model-like Higgs boson decays to two long-lived scalar particles that each decays to a quark-antiquark pair, branching fractions larger than 1% are excluded at 95% CL for mean proper decay lengths between 1 mm and 340 mm. A group of supersymmetric models with pair-produced long-lived gluinos or top squarks decaying into various final-state topologies containing displaced jets is also tested. Gluino masses up to 2500 GeV and top squark masses up to 1600 GeV are excluded at 95% CL for mean proper decay lengths between 3 and 300 mm. The highest lower bounds on mass reach 2600 GeV for long-lived gluinos and 1800 GeV for long-lived top squarks. These are the most stringent limits to date on these models. | ||
| Links: e-print arXiv:2012.01581 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The Feynman diagrams for the different long-lived models considered, including the jet-jet model (upper left), models with an exotic decay of the SM-like Higgs boson (upper right), general gauge mediation models with ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ decay (second row, left), mini-split SUSY with ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ decay (second row, right), RPV SUSY with ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ decay (third row, left), RPV SUSY with $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ decay (third row, right), RPV SUSY with $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ decay (lower left), and dRPV SUSY with $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ decay (lower right). |
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Figure 1-a:
Feynman diagram for the jet-jet model. |
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Figure 1-b:
Feynman diagram for models with an exotic decay of the SM-like Higgs boson. |
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Figure 1-c:
Feynman diagram for general gauge mediation models with ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ decay. |
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Figure 1-d:
Feynman diagram for mini-split SUSY with ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ decay. |
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Figure 1-e:
Feynman diagram for RPV SUSY with ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ decay. |
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Figure 1-f:
Feynman diagram for RPV SUSY with $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ decay. |
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Figure 1-g:
Feynman diagram for RPV SUSY with $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ decay. |
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Figure 1-h:
Feynman diagram for dRPV SUSY with $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ decay. |
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Figure 2:
Left : the NI-veto map based on the NI vertex reconstruction in the 2017 and 2018 data collected by the CMS detector, the map corresponds to the geometry of the CMS pixel detector used in 2017-2018 data taking [79]. The structures of the different pixel layers can be clearly seen. Right : the efficiency for a given vertex candidate to pass the NI-veto as a function of radius $r$. |
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Figure 2-a:
The NI-veto map based on the NI vertex reconstruction in the 2017 and 2018 data collected by the CMS detector, the map corresponds to the geometry of the CMS pixel detector used in 2017-2018 data taking [79]. The structures of the different pixel layers can be clearly seen. |
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Figure 2-b:
The efficiency for a given vertex candidate to pass the NI-veto as a function of radius $r$. |
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Figure 3:
The distributions of the vertex track multiplicity (upper left), vertex $L_{xy}$ significance (upper right), cluster RMS (lower left), and the magnitude of the signed ${\mathrm {Sig[IP_{2D}]}}$ sum $ {| \kappa |}$ (lower right), for data, simulated QCD multijet events, and simulated signal events. Data and simulated events are selected with the displaced-jet triggers and with the offline ${H_{\mathrm {T}}}$, jets ${p_{\mathrm {T}}}$, and $\eta $ selections applied. For a given event, if there is more than one SV candidate being reconstructed, the one with the largest vertex track multiplicity is chosen. If the track multiplicities are the same, the one with the smallest $\chi ^{2}/\mathrm {n_{dof}}$ is chosen. The lower panels show the ratios between the data and the simulated QCD multijet events. The blue shaded error bands and vertical bars represent the statistical uncertainties. Three benchmark signal distributions are shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and varying $c\tau _{0}$. For visualization purposes, each signal process is given a cross section that yields 10$^{6}$ events produced in the analyzed data sample. |
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Figure 3-a:
Distribution of the vertex track multiplicity, for data, simulated QCD multijet events, and simulated signal events. Data and simulated events are selected with the displaced-jet triggers and with the offline ${H_{\mathrm {T}}}$, jets ${p_{\mathrm {T}}}$, and $\eta $ selections applied. For a given event, if there is more than one SV candidate being reconstructed, the one with the largest vertex track multiplicity is chosen. If the track multiplicities are the same, the one with the smallest $\chi ^{2}/\mathrm {n_{dof}}$ is chosen. The lower panel shows the ratios between the data and the simulated QCD multijet events. The blue shaded error bands and vertical bars represent the statistical uncertainties. Three benchmark signal distributions are shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and varying $c\tau _{0}$. For visualization purposes, each signal process is given a cross section that yields 10$^{6}$ events produced in the analyzed data sample. |
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Figure 3-b:
Distribution of the vertex $L_{xy}$ significance, for data, simulated QCD multijet events, and simulated signal events. Data and simulated events are selected with the displaced-jet triggers and with the offline ${H_{\mathrm {T}}}$, jets ${p_{\mathrm {T}}}$, and $\eta $ selections applied. For a given event, if there is more than one SV candidate being reconstructed, the one with the largest vertex track multiplicity is chosen. If the track multiplicities are the same, the one with the smallest $\chi ^{2}/\mathrm {n_{dof}}$ is chosen. The lower panel shows the ratios between the data and the simulated QCD multijet events. The blue shaded error bands and vertical bars represent the statistical uncertainties. Three benchmark signal distributions are shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and varying $c\tau _{0}$. For visualization purposes, each signal process is given a cross section that yields 10$^{6}$ events produced in the analyzed data sample. |
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Figure 3-c:
Distribution of the cluster RMS, for data, simulated QCD multijet events, and simulated signal events. Data and simulated events are selected with the displaced-jet triggers and with the offline ${H_{\mathrm {T}}}$, jets ${p_{\mathrm {T}}}$, and $\eta $ selections applied. For a given event, if there is more than one SV candidate being reconstructed, the one with the largest vertex track multiplicity is chosen. If the track multiplicities are the same, the one with the smallest $\chi ^{2}/\mathrm {n_{dof}}$ is chosen. The lower panel shows the ratios between the data and the simulated QCD multijet events. The blue shaded error bands and vertical bars represent the statistical uncertainties. Three benchmark signal distributions are shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and varying $c\tau _{0}$. For visualization purposes, each signal process is given a cross section that yields 10$^{6}$ events produced in the analyzed data sample. |
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Figure 3-d:
Distribution of the magnitude of the signed ${\mathrm {Sig[IP_{2D}]}}$ sum $ {| \kappa |}$, for data, simulated QCD multijet events, and simulated signal events. Data and simulated events are selected with the displaced-jet triggers and with the offline ${H_{\mathrm {T}}}$, jets ${p_{\mathrm {T}}}$, and $\eta $ selections applied. For a given event, if there is more than one SV candidate being reconstructed, the one with the largest vertex track multiplicity is chosen. If the track multiplicities are the same, the one with the smallest $\chi ^{2}/\mathrm {n_{dof}}$ is chosen. The lower panel shows the ratios between the data and the simulated QCD multijet events. The blue shaded error bands and vertical bars represent the statistical uncertainties. Three benchmark signal distributions are shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and varying $c\tau _{0}$. For visualization purposes, each signal process is given a cross section that yields 10$^{6}$ events produced in the analyzed data sample. |
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Figure 4:
The distributions of the GBDT output score for data, simulated QCD multijet events, and simulated signal events. Data and simulated events are selected with the displaced-jet triggers and with the offline ${H_{\mathrm {T}}}$, jets ${p_{\mathrm {T}}}$, and $\eta $ selections applied. For a given event, if there is more than one SV candidate being reconstructed, the one with the largest vertex track multiplicity is chosen. If the track multiplicities are the same, the one with the smallest $\chi ^{2}/\mathrm {n_{dof}}$ is chosen. The lower panel shows the ratio between the data and the simulated QCD multijet events. The blue shaded error bands and vertical bars represent the statistical uncertainties. Three benchmark signal distributions are shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and varying $c\tau _{0}$. For visualization purposes, each signal process is given a cross section corresponding to 10$^{6}$ events produced in the analyzed data sample. The signal events shown in this plot are not used in the GBDT training. |
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Figure 5:
The predicted background yields and the numbers of observed events in the control region, for different bins of the GBDT scores. The background predictions in different bins are correlated, since the events that are used for background predictions in lower bins are also used in the background predictions in higher bins. The error bands for the predictions represent statistical uncertainties and systematic uncertainties added in quadrature. The error bars for the observed events represent statistical uncertainties, assuming Poisson statistics. |
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Figure 6:
The predicted background yields and the number of observed events for the data in the signal region, with $N_{\mathrm {tracks}}^{\mathrm {3D}}$ smaller than 3 for both jets, shown for different bins of the GBDT scores. The background predictions in different bins are correlated, since the events that are used for background predictions in lower bins are also used in the background predictions in higher bins. For comparison, three benchmark signal points are also shown (dashed lines) for the jet-jet model with $m_{\mathrm {X}} = $ 300 GeV and different lifetimes. For visualization purposes, each signal process is given a cross section that yields 100 events produced in the analyzed data sample. |
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Figure 7:
The 95% CL upper limits on the pair production cross section of the LLP $\mathrm {X}$, where a 100% branching fraction for $\mathrm {X}$ to decay to a quark-antiquark pair is assumed. Left : the upper limits as functions of $c\tau _{0}$ for different masses. Right : the upper limits as functions of the particle mass for different $c\tau _{0}$. The solid (dashed) curves show the observed (median expected) limits. The shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 7-a:
The 95% CL upper limits on the pair production cross section of the LLP $\mathrm {X}$, where a 100% branching fraction for $\mathrm {X}$ to decay to a quark-antiquark pair is assumed: the upper limits as functions of $c\tau _{0}$ for different masses. The solid (dashed) curves show the observed (median expected) limits. The shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 7-b:
The 95% CL upper limits on the pair production cross section of the LLP $\mathrm {X}$, where a 100% branching fraction for $\mathrm {X}$ to decay to a quark-antiquark pair is assumed: the upper limits as functions of the particle mass for different $c\tau _{0}$. The solid (dashed) curves show the observed (median expected) limits. The shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 8:
The expected and observed 95$%$ CL upper limits on the branching fraction of the SM-like Higgs boson to decay to two long-lived scalar particles, assuming the gluon-gluon fusion Higgs boson production cross section of 49 pb at 13 TeV with $m_{\mathrm{H}} = $ 125 GeV, shown at different masses and $c\tau _{0}$ for the scalar particle $\mathrm {S}$. Left : the upper limits when each scalar particle decays to a down quark-antiquark pair. Right : the upper limits when each scalar particle decays to a bottom quark-antiquark pair. The solid (dashed) curves represent the observed (median expected) limits. The shaded bands represent the regions containing 68% of the distributions of the expected limits under the background-only hypothesis. |
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Figure 8-a:
The expected and observed 95$%$ CL upper limits on the branching fraction of the SM-like Higgs boson to decay to two long-lived scalar particles, assuming the gluon-gluon fusion Higgs boson production cross section of 49 pb at 13 TeV with $m_{\mathrm{H}} = $ 125 GeV, shown at different masses and $c\tau _{0}$ for the scalar particle $\mathrm {S}$: the upper limits when each scalar particle decays to a down quark-antiquark pair. The solid (dashed) curves represent the observed (median expected) limits. The shaded bands represent the regions containing 68% of the distributions of the expected limits under the background-only hypothesis. |
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Figure 8-b:
The expected and observed 95$%$ CL upper limits on the branching fraction of the SM-like Higgs boson to decay to two long-lived scalar particles, assuming the gluon-gluon fusion Higgs boson production cross section of 49 pb at 13 TeV with $m_{\mathrm{H}} = $ 125 GeV, shown at different masses and $c\tau _{0}$ for the scalar particle $\mathrm {S}$: the upper limits when each scalar particle decays to a bottom quark-antiquark pair. The solid (dashed) curves represent the observed (median expected) limits. The shaded bands represent the regions containing 68% of the distributions of the expected limits under the background-only hypothesis. |
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Figure 9:
Left : the 95% CL upper limits on the pair production cross section for the long-lived gluinos with $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, where a 100% branching fraction for ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ decays is assumed. The NNLO$_{approx}$+NNLL gluino pair production cross sections for $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. The observed limits from the CMS search utilizing the timing capabilities of the ECAL system [48] are also shown for comparison. Right : the 95% CL upper limits on the pair production cross section for the ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ model as a function of the mean proper decay length $c\tau _{0}$ and the gluino mass $m_{{\mathrm{\widetilde{g}}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limit on the gluino mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 9-a:
The 95% CL upper limits on the pair production cross section for the long-lived gluinos with $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, where a 100% branching fraction for ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ decays is assumed. The NNLO$_{approx}$+NNLL gluino pair production cross sections for $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. The observed limits from the CMS search utilizing the timing capabilities of the ECAL system [48] are also shown for comparison. |
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Figure 9-b:
The 95% CL upper limits on the pair production cross section for the ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ model as a function of the mean proper decay length $c\tau _{0}$ and the gluino mass $m_{{\mathrm{\widetilde{g}}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limit on the gluino mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 10:
Left : the 95% CL upper limits on the pair production cross section for the long-lived gluinos with $m_{{\mathrm{\widetilde{g}}}} = $ 2400 GeV and 1600 GeV, where a 100% branching fraction for ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ decays is assumed. The NNLO$_{approx}$+NNLL gluino pair production cross sections for $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. Right : the 95% CL limits on the pair production cross section for the ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ model as a function of the mean proper decay length $c\tau _{0}$ and the gluino mass $m_{{\mathrm{\widetilde{g}}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the gluino mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 10-a:
The 95% CL upper limits on the pair production cross section for the long-lived gluinos with $m_{{\mathrm{\widetilde{g}}}} = $ 2400 GeV and 1600 GeV, where a 100% branching fraction for ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ decays is assumed. The NNLO$_{approx}$+NNLL gluino pair production cross sections for $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 10-b:
The 95% CL limits on the pair production cross section for the ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ model as a function of the mean proper decay length $c\tau _{0}$ and the gluino mass $m_{{\mathrm{\widetilde{g}}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the gluino mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 11:
Left : the 95% CL upper limits on the pair production cross section for the long-lived gluinos with $m_{{\mathrm{\widetilde{g}}}} = $ 2000 GeV and 1400 GeV, where a 100% branching fraction for ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ decays is assumed. The NNLO$_{approx}$+NNLL gluino pair production cross sections for $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. Right : the 95% CL limits on the pair production cross section for the ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ model as a function of the mean proper decay length $c\tau _{0}$ and the gluino mass $m_{{\mathrm{\widetilde{g}}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the gluino mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 11-a:
The 95% CL upper limits on the pair production cross section for the long-lived gluinos with $m_{{\mathrm{\widetilde{g}}}} = $ 2000 GeV and 1400 GeV, where a 100% branching fraction for ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ decays is assumed. The NNLO$_{approx}$+NNLL gluino pair production cross sections for $m_{{\mathrm{\widetilde{g}}}}= $ 2400 and 1600 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 11-b:
The 95% CL limits on the pair production cross section for the ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ model as a function of the mean proper decay length $c\tau _{0}$ and the gluino mass $m_{{\mathrm{\widetilde{g}}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the gluino mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 12:
Left : the 95% CL upper limits on the pair production cross section for the long-lived top squarks with $m_{\tilde{\mathrm{t}}} = $ 1600 GeV and 800 GeV, where a 100% branching fraction for $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ decays is assumed, with equal branching fractions for e, $\mu $, and $\tau $. The NNLO$_{approx}$+NNLL top squark pair production cross sections for $m_{\tilde{\mathrm{t}}}=1600$ and 1000 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. Right : the 95% CL limits on the pair production cross section for the $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ model as a function of the mean proper decay length $c\tau _{0}$ and the top squark mass $m_{\tilde{\mathrm{t}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the top squark mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 12-a:
The 95% CL upper limits on the pair production cross section for the long-lived top squarks with $m_{\tilde{\mathrm{t}}} = $ 1600 GeV and 800 GeV, where a 100% branching fraction for $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ decays is assumed, with equal branching fractions for e, $\mu $, and $\tau $. The NNLO$_{approx}$+NNLL top squark pair production cross sections for $m_{\tilde{\mathrm{t}}}=1600$ and 1000 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 12-b:
The 95% CL limits on the pair production cross section for the $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ model as a function of the mean proper decay length $c\tau _{0}$ and the top squark mass $m_{\tilde{\mathrm{t}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the top squark mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 13:
Left : the 95% CL upper limits on the pair production cross section for the long-lived top squarks with $m_{\tilde{\mathrm{t}}} = $ 1600 GeV and 800 GeV, where a 100% branching fraction for $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ decays is assumed, with equal branching fractions for e, $\mu $, and $\tau $. The NNLO$_{approx}$+NNLL top squark pair production cross sections for $m_{\tilde{\mathrm{t}}}=1600$ and 1000 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. Right : the 95% CL limits on the pair production cross section for the $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ model as a function of the mean proper decay length $c\tau _{0}$ and the top squark mass $m_{\tilde{\mathrm{t}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the top squark mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 13-a:
The 95% CL upper limits on the pair production cross section for the long-lived top squarks with $m_{\tilde{\mathrm{t}}} = $ 1600 GeV and 800 GeV, where a 100% branching fraction for $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ decays is assumed, with equal branching fractions for e, $\mu $, and $\tau $. The NNLO$_{approx}$+NNLL top squark pair production cross sections for $m_{\tilde{\mathrm{t}}}=1600$ and 1000 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 13-b:
The 95% CL limits on the pair production cross section for the $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ model as a function of the mean proper decay length $c\tau _{0}$ and the top squark mass $m_{\tilde{\mathrm{t}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the top squark mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 14:
Left : the 95% CL upper limits on the pair production cross section for the long-lived top squarks with $m_{\tilde{\mathrm{t}}} = $ 1600 GeV and 800 GeV, where a 100% branching fraction for $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ decays is assumed. The NNLO$_{approx}$+NNLL top squark pair production cross sections for $m_{\tilde{\mathrm{t}}}=1600$ and 1000 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. Right : the 95% CL limits on the pair production cross section for the $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ model as a function of the mean proper decay length $c\tau _{0}$ and the top squark mass $m_{\tilde{\mathrm{t}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the top squark mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure 14-a:
The 95% CL upper limits on the pair production cross section for the long-lived top squarks with $m_{\tilde{\mathrm{t}}} = $ 1600 GeV and 800 GeV, where a 100% branching fraction for $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ decays is assumed. The NNLO$_{approx}$+NNLL top squark pair production cross sections for $m_{\tilde{\mathrm{t}}}=1600$ and 1000 GeV, as well as their variations due to the theoretical uncertainties, are shown as horizontal lines. The solid (dashed) curves show the observed (median expected) limits, and the shaded bands indicate the regions containing 68% of the distributions of the limits expected under the background-only hypothesis. |
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Figure 14-b:
The 95% CL limits on the pair production cross section for the $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ model as a function of the mean proper decay length $c\tau _{0}$ and the top squark mass $m_{\tilde{\mathrm{t}}}$. The thick solid black (dashed red) curve shows the observed (median expected) 95% CL limits on the top squark mass as a function of $c\tau _{0}$, assuming the NNLO$_{approx}$+NNLL cross sections. The thin dashed red curves indicate the region containing 68% of the distribution of the limits expected under the background-only hypothesis. The thin solid black curves represent the change in the observed limit when the signal cross sections are varied according to their theoretical uncertainties. |
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Figure A1:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ model (upper left), the ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ model (upper right), the ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ model (middle left), the $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ model (middle right), the $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ model (lower left), and the $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ model (lower right). |
png pdf |
Figure A1-a:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ model. |
png pdf |
Figure A1-b:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ model. |
png pdf |
Figure A1-c:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ model. |
png pdf |
Figure A1-d:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ model. |
png pdf |
Figure A1-e:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ model. |
png pdf |
Figure A1-f:
The signal efficiencies as functions of the long-lived particle mass and mean proper decay length in the 2017 and 2018 analysis, for the $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ model. |
| Tables | |
png pdf |
Table 1:
Summary of the preselection criteria. |
png pdf |
Table 2:
The definitions of the different regions used in the background estimation. |
png pdf |
Table 3:
Summary of the systematic uncertainties in the signal yields. |
png pdf |
Table 4:
Event yields after different selection requirements have been applied for data collected in 2017 and 2018. Signal efficiencies for the jet-jet model with $m_{\mathrm {X}} = $ 1000 GeV and different $c\tau _{0}$ are also shown for comparison. Selection requirements are cumulative from the first row to the last. |
png pdf |
Table A1:
Signal efficiencies for the jet-jet model in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{\mathrm {X}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{\mathrm {X}}$. Uncertainties are statistical only. |
png pdf |
Table A2:
Signal efficiencies for the model where the SM-like Higgs boson decays to two long-lived scalar particles $\mathrm {S}$ in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and with $m_{\mathrm {S}} = $ 55 GeV. The long-lived scalar particle is assumed to decay to a down quark-antiquark pair ($\mathrm {S}\to \mathrm{d} \mathrm{\bar{d}} $). Selection requirements are cumulative from the first row to the last. Uncertainties are statistical only. |
png pdf |
Table A3:
Signal efficiencies for the model where the SM-like Higgs boson decays to two long-lived scalar particles $\mathrm {S}$ in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and with $m_{\mathrm {S}} = $ 55 GeV. The long-lived scalar particle is assumed to decay to a bottom quark-antiquark pair ($\mathrm {S}\to \mathrm{b} \mathrm{\bar{b}} $). Selection requirements are cumulative from the first row to the last. Uncertainties are statistical only. |
png pdf |
Table A4:
Signal efficiencies for the ${\mathrm{\widetilde{g}}} \to \mathrm{g} \tilde{\mathrm{G}} $ model in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{{\mathrm{\widetilde{g}}}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{{\mathrm{\widetilde{g}}}}$. Uncertainties are statistical only. |
png pdf |
Table A5:
Signal efficiencies for the ${\mathrm{\widetilde{g}}} \to \mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^{0}_{1}$ model ($m_{\tilde{\chi}^{0}_{1}} = $ 100 GeV) in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{{\mathrm{\widetilde{g}}}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{{\mathrm{\widetilde{g}}}}$. Uncertainties are statistical only. |
png pdf |
Table A6:
Signal efficiencies for the ${\mathrm{\widetilde{g}}} \to \mathrm{t} \mathrm{b} \mathrm{s} $ model in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{{\mathrm{\widetilde{g}}}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{{\mathrm{\widetilde{g}}}}$. Uncertainties are statistical only. |
png pdf |
Table A7:
Signal efficiencies for the $\tilde{\mathrm{t}} \to \mathrm{b} \ell $ model in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{\tilde{\mathrm{t}}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{\tilde{\mathrm{t}}}$. Uncertainties are statistical only. |
png pdf |
Table A8:
Signal efficiencies for the $\tilde{\mathrm{t}} \to \mathrm{d} \ell $ model in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{\tilde{\mathrm{t}}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{\tilde{\mathrm{t}}}$. Uncertainties are statistical only. |
png pdf |
Table A9:
Signal efficiencies for the $\tilde{\mathrm{t}} \to \mathrm{\bar{d}} \mathrm{\bar{d}} $ model in the 2017 and 2018 analysis at different mean proper decay lengths $c\tau _{0}$ and different masses $m_{\tilde{\mathrm{t}}}$. Selection requirements are cumulative from the first row to the last for each value of $m_{\tilde{\mathrm{t}}}$. Uncertainties are statistical only. |
| Summary |
|
A search has been presented for long-lived particles decaying to jets, using proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV in 2017 and 2018. The results are combined with those of a previous CMS search for displaced jets using proton-proton collision data from 2016, accumulating to a total integrated luminosity of 132 fb$^{-1}$. After all selections, one event is observed in the data collected in 2017 and 2018, which is consistent with the predicted background yield. The search is designed to be model independent, and is sensitive to a large number of models predicting displaced-jets signatures with different final-state topologies. The best current limits are set on a variety of models that have long-lived particles with mean proper decay lengths between 1 mm and 10 m. All limits are computed at the 95% confidence level. For a simplified model where pair-produced long-lived neutral particles decay to quark-antiquark pairs, pair production cross sections larger than 0.07 fb are excluded for mean proper decay lengths between 2 and 250 mm at high mass ($m_{\mathrm{X}} > $ 500 GeV). For a model where the standard model-like Higgs boson decays to two long-lived scalar particles and each long-lived scalar particle decays to a down (bottom) quark-antiquark pair, branching fractions for the exotic Higgs boson decay larger than 1% (10%) are excluded for mean proper decay lengths between 1 and 340 mm (530 mm) when the scalar particle mass is larger than 40 GeV. For a supersymmetric (SUSY) model in the general gauge mediation scenario, where the long-lived gluino decays to a gluon and a lightest SUSY particle, gluino masses up to 2450 GeV are excluded for mean proper decay lengths between 6 and 550 mm. For another SUSY model in the mini-split scenario, where the long-lived gluino can decay to a quark-antiquark pair and the lightest neutralino, gluino masses up to 2500 GeV are excluded for mean proper decay lengths between 7 and 360 mm. An $R$-parity violating (RPV) SUSY model is also tested, where the long-lived gluino can decay to top, bottom, and strange antiquarks, and gluino masses up to 2500 GeV are excluded for mean proper decay lengths between 3 and 1000 mm. Another RPV SUSY model is studied, where the long-lived top squark can decay to a bottom quark and a charged lepton, and top squark masses up to 1600 GeV are excluded for mean proper decay lengths between 5 and 240 mm. For an RPV SUSY model, where the long-lived top squark can decay to a down quark and a charged lepton, top squark masses up to 1600 GeV are excluded for mean proper decay lengths between 3 and 360 mm. Finally, for a dynamical-RPV SUSY model, where the long-lived top squark can decay to two down antiquarks, top squark masses up to 1600 GeV are excluded for mean proper decay lengths between 2 and 1320 mm. These are the most stringent limits to date on these models. |
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