CMS-PAS-SUS-16-032

CMS-PAS-SUS-16-032
Search for direct production of bottom and top squark pairs in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
March 2017

Abstract: This note presents a search for direct production of bottom or top squark pairs in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=$ 13 TeV collected by the CMS experiment at the LHC in 2016. The data used correspond to an integrated luminosity of 36 fb $^{-1}$ . This search is performed in a final state of two, three, or four jets accompanied by a significant imbalance in the transverse momentum. No statistically significant excess of events is found beyond the expected contribution from standard model processes. Exclusion limits are set in the context of simplified models of bottom- or top-squark pair production. Bottom squarks with masses below 1225 GeV are excluded at 95%CL for small values of the neutralino mass. Top squarks with masses below 525 GeV are excluded if the mass difference to the lightest neutralino is close to 10 GeV.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 778 (2018) 263. The superseded preliminary plots can be found here.

Figures & Tables	Summary	Additional Figures & Tables	References	CMS Publications

Additional information on efficiencies needed for reinterpretation of these results are available here.

Figures
png pdf	Figure 1: Diagrams showing the pair production of top or bottom squarks followed by their decays according to $\tilde{ \mathrm{ b } } \rightarrow \mathrm{ b } \tilde{\chi}^{0} _1$ (left) and $\tilde{ \mathrm{ t } } \rightarrow \tilde{\mathrm{c}} \tilde{\chi}^{0} _1$ (right).
png pdf	Figure 1-a: Diagram showing the pair production of bottom squarks followed by their decays according to $\tilde{ \mathrm{ b } } \rightarrow \mathrm{ b } \tilde{\chi}^{0} _1$ .
png pdf	Figure 1-b: Diagram showing the pair production of top squarks followed by their decays according to $\tilde{ \mathrm{ t } } \rightarrow \tilde{\mathrm{c}} \tilde{\chi}^{0} _1$ .
png pdf	Figure 2: Distribution of ${m_{\mathrm {CT}}}$ (left) and ${H_{\mathrm {T}}}$ (right) for the search in the non-compressed region as obtained from simulation. The stacked, filled histograms represent different background components while the lines show three different model points for bottom squark production.
png pdf	Figure 2-a: Distribution of ${m_{\mathrm {CT}}}$ for the search in the non-compressed region as obtained from simulation. The stacked, filled histograms represent different background components while the lines show three different model points for bottom squark production.
png pdf	Figure 2-b: Distribution of ${H_{\mathrm {T}}}$ for the search in the non-compressed region as obtained from simulation. The stacked, filled histograms represent different background components while the lines show three different model points for bottom squark production.
png pdf	Figure 3: Distributions of the combined b-, c-tagged jet, and SV multiplicity (left), and ${E_{ \mathrm {T}}^{ \mathrm {miss}}}$ for events with at least one b- or c-tagged jet (right) after the baseline selection for the compressed region as obtained from simulation. The stacked, filled histograms represent different background components while the lines show three different model points for bottom squark production.
png pdf	Figure 3-a: Distributions of the combined b-, c-tagged jet, and SV multiplicity after the baseline selection for the compressed region as obtained from simulation. The stacked, filled histograms represent different background components while the lines show three different model points for bottom squark production.
png pdf	Figure 3-b: Distributions of ${E_{ \mathrm {T}}^{ \mathrm {miss}}}$ for events with at least one b- or c-tagged jet after the baseline selection for the compressed region as obtained from simulation. The stacked, filled histograms represent different background components while the lines show three different model points for bottom squark production.
png pdf	Figure 4: Yields in the signal regions targeting the non-compressed (top left) and compressed (top right: ${N_{\mathrm {b-tags}}} =$ 1, 2, bottom left: ${N_{\mathrm {c-tags}}} =$ 1, 2, bottom right: ${N_{\mathrm {b-tags}}} + {N_{\mathrm {c-tags}}} =$ 0) scenarios. Data are shown as black points. The background predictions are represented by the stacked, filled histograms. The expected yields for two signal models are also shown. The lower panels show the ratio of data over total background prediction in each signal region.
png pdf	Figure 4-a: Yields in the signal region targeting the non-compressed scenario. Data are shown as black points. The background predictions are represented by the stacked, filled histograms. The expected yields for two signal models are also shown. The lower panel shows the ratio of data over total background prediction.
png pdf	Figure 4-b: Yields in the signal region targeting the compressed with ${N_{\mathrm {b-tags}}} =$ 1, 2 scenario. Data are shown as black points. The background predictions are represented by the stacked, filled histograms. The expected yields for two signal models are also shown. The lower panel shows the ratio of data over total background prediction.
png pdf	Figure 4-c: Yields in the signal region targeting the non-compressed compressed with ${N_{\mathrm {c-tags}}} =$ 1, 2 scenario. Data are shown as black points. The background predictions are represented by the stacked, filled histograms. The expected yields for two signal models are also shown. The lower panel shows the ratio of data over total background prediction.
png pdf	Figure 4-d: Yields in the signal region targeting the compressed with ${N_{\mathrm {b-tags}}} + {N_{\mathrm {c-tags}}} =$ 0) scenario. Data are shown as black points. The background predictions are represented by the stacked, filled histograms. The expected yields for two signal models are also shown. The lower panel shows the ratio of data over total background prediction.
png pdf	Figure 5: The 95% CL limits on the cross section, assuming 100% BR for the decay of the top squark shown in the legend (left). The combined 95% CL exclusion limits for top squark pair production assuming 100% branching fraction to the decay $\tilde{ \mathrm{ t } } \rightarrow \tilde{\mathrm{c}} \tilde{\chi}^{0} _1$ (right). The mass limits are shown as a black line for the observed limit and as a red line for the expected limit.
png pdf root	Figure 5-a: The 95% CL limits on the cross section, assuming 100% BR for the decay of the top squark shown in the legend. The mass limits are shown as a black line for the observed limit and as a red line for the expected limit.
png pdf root	Figure 5-b: The combined 95% CL exclusion limits for top squark pair production assuming 100% branching fraction to the decay $\tilde{ \mathrm{ t } } \rightarrow \tilde{\mathrm{c}} \tilde{\chi}^{0} _1$ . The mass limits are shown as a black line for the observed limit and as a red line for the expected limit.
png pdf	Figure 6: The covariance and correlation matrices for the estimated backgrounds in the compressed and non-compressed search regions.
png pdf root	Figure 6-a: The covariance matrix for the estimated backgrounds in the compressed search region.
png pdf root	Figure 6-b: The correlation matrix for the estimated backgrounds in the compressed search region.
png pdf root	Figure 6-c: The covariance matrix for the estimated backgrounds in the non-compressed search region.
png pdf root	Figure 6-d: The correlation matrix for the estimated backgrounds in the non-compressed search region.

Tables
png pdf	Table 1: The ${m_{\mathrm {CT}}}$ and ${H_{\mathrm {T}}}$ signal bins in the non-compressed search region.
png pdf	Table 2: The signal bin definitions in the compressed search region.
png pdf	Table 3: Baseline selections in both the non-compressed and compressed regions.
png pdf	Table 4: Typical ranges for the different systematic uncertainties on the lost lepton background estimate.
png pdf	Table 5: Observed number of events and background prediction (individual, total) in the non-compressed region. The uncertainties shown combine the statistical and systematic components.
png pdf	Table 6: Observed number of events and background prediction (individual and total) in the compressed region with ${N_{\mathrm {b-tags}}} =$ 1, 2. the uncertainties shown combine the statistical and systematic components.
png pdf	Table 7: Observed number of events and background prediction (individual and total) in the compressed region with ${N_{\mathrm {c-tags}}} =$ 1, 2. The uncertainties shown combine the statistical and systematic components.
png pdf	Table 8: Observed number of events and background prediction (individual and total) in the compressed region with ${N_{\mathrm {b-tags}}} + {N_{\mathrm {c-tags}}} =$ 0. The uncertainties shown combine the statistical and systematic components.
png pdf	Table 9: The bin number and definition in the compressed search region.

Summary

A search for pair production of bottom and top squarks is reported, based on a data sample of pp collisions collected with the CMS detector at

$\sqrt{s} =$ 13 TeV in 2016, corresponding to an integrated luminosity of 36 fb

$^{-1}$ . Final states with two, three, and four jets, two of which originate from b or c quarks, and significant

${E_{\, \mathrm{T}}^{\, \mathrm{miss}}}$ have been analyzed. The search has been performed in exclusive binned signal regions defined by the number of jets identified as originating from a b or c quark, missing energy, scalar sum of the jets

$p_{\mathrm{T}}$ , and the contransverse mass. The standard model backgrounds per bin have been estimated from data control samples. We observe no excess above the SM predictions. Exclusion limits are set at the 95% CL on the simplified model production of a pair of bottom (top) squarks, with each bottom (top) squark decaying to a bottom (charm) quark and the lightest neutralino. The production of bottom squarks with masses up to 1225 GeV is excluded at 95% confidence level for neutralino masses less than 100 GeV. Top squarks with masses below 525 GeV are excluded if mass splitting between a top squark and an LSP is close to 10 GeV.

Additional Figures
png pdf	Additional Figure 1: Observed significances for simplified models of top squark pair production in the $\tilde{ \mathrm{ b } } \rightarrow \mathrm{ b } \tilde{\chi}^{0} _1$ ("T2bb") decay scenario.
png pdf	Additional Figure 2: Observed significances for simplified models of top squark pair production in the $\tilde{ \mathrm{ t } } \rightarrow \tilde{\mathrm{c}} \tilde{\chi}^{0} _1$ ("T2cc") decay scenario.

Additional Tables
png pdf	Additional Table 1: Event yields from simulation for two signal points ( $m_{\tilde{ \mathrm{ b } } } =$ 900 GeV and $m_{\tilde{\chi}^{0} _1} =$ 300 GeV) and ( $m_{\tilde{ \mathrm{ b } } } =$ 1200 GeV and $m_{\tilde{\chi}^{0} _1} =$ 100 GeV) after applying each requirement in the non-compressed search region. The numbers are normalized to an integrated luminosity of 36 fb $^{-1}$ and the uncertainties correspond to statistical uncertainty from the MC samples.
png pdf	Additional Table 2: Event yields from simulation for two signal points ( $m_{\tilde{ \mathrm{ b } } } =$ 550 GeV and $m_{\tilde{\chi}^{0} _1} =$ 500 GeV) and ( $m_{\tilde{ \mathrm{ t } } } =$ 400 GeV and $m_{\tilde{\chi}^{0} _1} =$ 370 GeV) after applying each requirement in the compressed search region. The numbers are normalized to an integrated luminosity of 36 fb $^{-1}$ and the uncertainties correspond to statistical uncertainty from the MC samples.

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