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| CMS-PAS-SUS-21-003 | ||
| Search for top squarks decaying via the four-body mode in single-lepton final states from Run 2 of the LHC | ||
| CMS Collaboration | ||
| June 2022 | ||
| Abstract: Results are presented from a search for the pair production of the lightest supersymmetric partner of the top quark ($\mathrm{\tilde{t}}_{1}$). The search targets the four-body decay of the $\mathrm{\tilde{t}}_{1}$, which is allowed when the mass difference between the top squark and the lightest supersymmetric particle is smaller than the mass of the W boson. This decay mode consists of a bottom quark, two other fermions, and a $\tilde{\chi}^{0}_{1}$, often considered to be the lightest supersymmetric particle. The data correspond to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector. The signature of the selected events is defined by a high-momentum jet, significant missing transverse momentum, and a low transverse momentum electron or muon. The selection of the signal is based on a multivariate approach that is adapted to the $m(\mathrm{\tilde{t}}_{1}) - m(\tilde{\chi}^{0}_{1})$ mass difference. Leading background processes are determined from data. No significant excess in data is observed above the expectation from standard model processes. The results of this search exclude top squark masses up to 700 GeV, depending on the $m(\mathrm{\tilde{t}}_{1}) - m(\tilde{\chi}^{0}_{1})$ mass difference. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 06 (2023) 060. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Top squark pair production at the LHC with four-body decays. |
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Figure 2:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 2-a:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 2-b:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 2-c:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 2-d:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 2-e:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 2-f:
Distributions of ${{p_{\mathrm {T}}} (\ell)}$ (left), ${{p_{\mathrm {T}}} ^\text {miss}}$ (middle), and ${N_{\text {jets}}}$ (right), for the data of 2017 (top) and 2018 (bottom) at the preselection level in data and simulation. The background distributions are obtained directly from simulation, and are normalized to an integrated luminosity of 41.5 fb$^{-1}$ and 59.8 fb$^{-1}$ for 2017 and 2018, respectively. The distributions of two signal points are represented, while not being added to the background: ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))} =$ (500, 490) and (500, 420) GeV. The last bin in each plot includes the overflow events. The lower panels show the ratio of data to the sum of the SM backgrounds, where the dark shaded bands indicate the statistical uncertainties of simulated data. |
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Figure 3:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 3-a:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 3-b:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 3-c:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 3-d:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 3-e:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 3-f:
Simulated distribution of ${{p_{\mathrm {T}}} (\ell)}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, and ${N_{\text {jets}}}$ at the preselection level. The area of each signal distribution and the total background are normalized to unit area. Top: Each distribution is shown for signal samples with $ {\Delta {m}}=$ 10, 30, 50, and 80 GeV, as well as the W+jets and ${\mathrm{t} \mathrm{\bar{t}}}$ background processes. Bottom: Each distribution is shown for various signal points with the same $ {\Delta {m}}=$ 30 GeV. |
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Figure 4:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-a:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-b:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-c:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-d:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-e:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-f:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-g:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 4-h:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2017. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-a:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-b:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-c:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-d:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-e:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-f:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-g:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 5-h:
Distributions of the BDT output at the preselection level in data and simulation in 10 GeV steps of ${\Delta {m}}$ from 10 (top-left) to 80 GeV (bottom-right) for the data of 2018. The last bin represents the SR. For each BDT training, a representative ${({m}({\tilde{\mathrm{t}} _{1}}), {m}(\tilde{\chi}^0_1))}$ signal point is also presented, while not added to the SM background. The shaded area on the Data/MC ratio represents the statistical uncertainty of the simulated background. |
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Figure 6:
2017 analysis: Prediction of the total background and its composition in the eight SRs as defined in Table 2. The predictions of W+jets, ${\mathrm{t} \mathrm{\bar{t}}}$, and nonprompt lepton processes are based on data, while that of rare backgrounds is based on simulation. The predictions and their associated uncertainties are pre-fit, as in Table 2. The yield of two signal points, with $ {\Delta {m}}= $ 10 and $ {\Delta {m}}= $ 80 GeV, is also represented. The bins corresponding to different ${\Delta {m}}$ trainings are not statistically independent. The lower panel shows the ratio of the number of observed events over the predicted total background per SR. |
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Figure 7:
2018 analysis: Prediction of the total background and its composition in the eight SRs as defined in Table 3. The predictions of W+jets, ${\mathrm{t} \mathrm{\bar{t}}}$, and nonprompt lepton processes are based on data, while that of rare backgrounds is based on simulation. The predictions and their associated uncertainties are pre-fit, as in Table 3. The yield of two signal points, with $ {\Delta {m}}= $ 10 and $ {\Delta {m}}= $ 80 GeV, is also represented. The bins corresponding to different ${\Delta {m}}$ trainings are not statistically independent. The lower panel shows the ratio of the number of observed events over the predicted total background per SR. |
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Figure 8:
Exclusion limit at 95% CL for the four-body decay of the top squark as a function of $m({\tilde{\mathrm{t}} _{1}})$ and ${\Delta {m}}$ for the data of Run 2. The color shading represents the observed limit on the cross section. The solid black and dashed red lines represent the observed and expected limits, respectively. These limits are derived using the expected top squark pair production cross section. The thick lines represent the central values, and the thin lines the variations due to the theoretical or experimental uncertainties. |
| Tables | |
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Table 1:
Relative systematic uncertainties (in %) on the total background, and signal prediction for the 2017 (left) and 2018 (right) data analysis. The "---'' means that a given source of uncertainty is not applicable. In the case of the background, the uncertainties are on the total background. The range of each systematic uncertainty is provided across the eight SRs. |
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Table 2:
2017 analysis: Prediction of the W+jets, ${\mathrm{t} \mathrm{\bar{t}}}$, nonprompt lepton, and other backgrounds in the eight SRs defined by the threshold on the BDT output reported in the second column. The prediction of the first three processes is data driven, while that of rare backgrounds, $N^{SR}(\text {Rare})$, is based on simulation. The uncertainties are the quadrature sum of the statistical uncertainties, the systematic uncertainties of Table 1, and for the backgrounds predicted from simulation, the cross section uncertainties. The number of total expected background ($N^{SR}\text {(B)}$) and observed data ($N^{SR}\text {(D)}$) events in each SR are also reported. |
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Table 3:
2018 analysis: Prediction of the W+jets, ${\mathrm{t} \mathrm{\bar{t}}}$, nonprompt lepton, and other backgrounds in the eight SRs defined by the threshold on the BDT output reported in the second column. The prediction of the first three processes is data driven, while that of rare backgrounds, $N^{SR}(\text {Rare})$, is based on simulation. The uncertainties are the quadrature sum of the statistical uncertainties, the systematic uncertainties of Table 1, and for the backgrounds predicted from simulation, the cross section uncertainties. The number of total expected background ($N^{SR}\text {(B)}$) and observed data ($N^{SR}\text {(D)}$) events in each SR are also reported. |
| Summary |
|
A search for the direct pair production of top squarks is performed in a compressed scenario where the mass difference ${\Delta {m}} = m({\tilde{\mathrm{t}}_{1}} ) - m(\tilde{\chi}^0_1)$ between the lightest top squark and the lightest supersymmetric particle, taken to be the lightest neutralino $\tilde{\chi}^0_1$, does not exceed the W boson mass. The considered decay mode of the top squark is the prompt four-body decay to $\mathrm{b} \mathrm{f} \overline{\mathrm{f}}^{\,\prime} \tilde{\chi}^0_1$. The result is based on data collected from proton-proton collisions at $\sqrt{s} = $ 13 TeV, recorded with the CMS detector during the Run 2 of the LHC, and corresponds to an integrated luminosity of 138 fb$^{-1}$. Events are selected where the presence of a single lepton (electron or muon), at least one high-momentum jet, and significant missing transverse momentum are required. The search strategy is based on a multivariate tool that is specifically trained for different ${\Delta {m}}$ regions, thus adapting the selection of th e signal to the evolution of its kinematics through the mmplane plane. The dominant background processes in this search are W+jets, $\mathrm{t\bar{t}}$, and events with nonprompt leptons, and are predicted from control regions in data. After the final selection, data are compatible with the predicted backgrounds stemming from the standard model in all signal regions. Limits are therefore set at 95% confidence level on the production cross section as a function of the ${\tilde{\mathrm{t}}_{1}}$ and $\tilde{\chi}^0_1$ masses, within the context of simplified models. Assuming 100% branching fraction in the four-body decay mode, and computing the top squark pair production cross section at next-to-next-to-leading order accuracy plus next-to-next-to-leading logarithmic precision [26,27,28,29,30,31,32], these limits are translated into mass limits. The search excludes top squark masses up to 480 and 700 GeV at ${\Delta {m}}$ = 10 and 80 GeV, respectively. The results summarized in this note represent the most stringent limits to date on the top squark pair production cross section, where the top squark decays via the four-body mode. |
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