CMS-PAS-SUS-16-011

CMS-PAS-SUS-16-011
Search for new physics in the one soft lepton final state using 2015 data at $\sqrt{s}=$ 13 TeV
CMS Collaboration
June 2016

Abstract: This note presents the results of a search for new physics using events with one soft lepton and large missing transverse momentum, inclusive in jet flavor and multiplicity. Results are based on a 2.3 fb$^{-1}$ data sample of $\sqrt{s} =$ 13 TeV proton-proton collisions collected with the CMS detector. No significant deviations from the standard model expectations are observed, and the results are used to set limits on models featuring compressed spectra. For pair production of top squarks decaying into four bodies, $\widetilde{t} \rightarrow b \widetilde\chi^{0} l (q) \nu (q^\prime)$, top squark masses below 340 GeV are excluded for $m_{\widetilde{t}} - m_{\widetilde\chi^{0}} =$ 50 GeV. For gluino pair production decaying to $\widetilde{g} \rightarrow q\bar{q} \widetilde\chi^{\pm}$ followed by $\widetilde\chi^{\pm} \rightarrow W^{*} \widetilde\chi^{0}$, with $m_{\widetilde\chi^{\pm}} - m_{\widetilde\chi^{0}} =$ 20 GeV, gluino masses in the range 900-1200 GeV are excluded for $\widetilde\chi^{0}$ masses in the range 100-800 GeV.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png	Figure 1-a: Feynman diagrams illustrating the signal processes considered. The left diagram depicts the 4-body decay of the top squark, $\widetilde{t} \rightarrow b \tilde{ \chi }^{0} l (q) \nu (q\prime )$. The right diagram depicts gluino pair-production, where the gluinos always decay through a chargino to a W and LSP, $\widetilde{g} \rightarrow q\bar{q} \widetilde{\chi} ^{0} $. Both models can decay into final states with 0, 1, or 2 leptons.
png pdf	Figure 1-b: Feynman diagrams illustrating the signal processes considered. The left diagram depicts the 4-body decay of the top squark, $\widetilde{t} \rightarrow b \tilde{ \chi }^{0} l (q) \nu (q\prime )$. The right diagram depicts gluino pair-production, where the gluinos always decay through a chargino to a W and LSP, $\widetilde{g} \rightarrow q\bar{q} \widetilde{\chi} ^{0} $. Both models can decay into final states with 0, 1, or 2 leptons.
png pdf	Figure 2-a: Comparison of estimated background, pre-fit (a) and post-fit (b), and observed data events in each signal region. The ${m_{\mathrm {T}}}$ ranges are shown on the $x$-axis. The grey band in the pre-fit histogram includes the total uncertainty assigned to each background, while in the post-fit histogram it represents the uncertainty measured by the background-only fit.
png pdf	Figure 2-b: Comparison of estimated background, pre-fit (a) and post-fit (b), and observed data events in each signal region. The ${m_{\mathrm {T}}}$ ranges are shown on the $x$-axis. The grey band in the pre-fit histogram includes the total uncertainty assigned to each background, while in the post-fit histogram it represents the uncertainty measured by the background-only fit.
png pdf	Figure 3-a: Exclusion limits at 95% CL for top squark (a) and gluino (b) production. The color axis indicates the excluded cross section, while the red and black lines show the expected and observed mass values for which the excluded cross-section is equal to the predicted cross section of the model. The area to the left and below the lines represents the exclusion region.
png pdf	Figure 3-b: Exclusion limits at 95% CL for top squark (a) and gluino (b) production. The color axis indicates the excluded cross section, while the red and black lines show the expected and observed mass values for which the excluded cross-section is equal to the predicted cross section of the model. The area to the left and below the lines represents the exclusion region.
png pdf	Figure 4-a: Comparisons of estimated backgrounds and observed data events in the sum of all signal regions, as a function number of jets (a) heavy flavor category (b), ${E_{\mathrm {T}}^{\text {miss}}}$ (c), ${m_{\mathrm {T}}(\vec{\ell} , {\vec{p}_{ \mathrm {T}}^{ \mathrm {miss}}} )}$ (d). Each estimated background distribution is formed by summing the MC shapes for all signal regions, where each MC shape is first scaled to the predicted background (pre-fit) in that region. The grey band represents the statistical and systematic uncertainty on the estimates.
png pdf	Figure 4-b: Comparisons of estimated backgrounds and observed data events in the sum of all signal regions, as a function number of jets (a) heavy flavor category (b), ${E_{\mathrm {T}}^{\text {miss}}}$ (c), ${m_{\mathrm {T}}(\vec{\ell} , {\vec{p}_{ \mathrm {T}}^{ \mathrm {miss}}} )}$ (d). Each estimated background distribution is formed by summing the MC shapes for all signal regions, where each MC shape is first scaled to the predicted background (pre-fit) in that region. The grey band represents the statistical and systematic uncertainty on the estimates.
png pdf	Figure 4-c: Comparisons of estimated backgrounds and observed data events in the sum of all signal regions, as a function number of jets (a) heavy flavor category (b), ${E_{\mathrm {T}}^{\text {miss}}}$ (c), ${m_{\mathrm {T}}(\vec{\ell} , {\vec{p}_{ \mathrm {T}}^{ \mathrm {miss}}} )}$ (d). Each estimated background distribution is formed by summing the MC shapes for all signal regions, where each MC shape is first scaled to the predicted background (pre-fit) in that region. The grey band represents the statistical and systematic uncertainty on the estimates.
png pdf	Figure 4-d: Comparisons of estimated backgrounds and observed data events in the sum of all signal regions, as a function number of jets (a) heavy flavor category (b), ${E_{\mathrm {T}}^{\text {miss}}}$ (c), ${m_{\mathrm {T}}(\vec{\ell} , {\vec{p}_{ \mathrm {T}}^{ \mathrm {miss}}} )}$ (d). Each estimated background distribution is formed by summing the MC shapes for all signal regions, where each MC shape is first scaled to the predicted background (pre-fit) in that region. The grey band represents the statistical and systematic uncertainty on the estimates.

Tables
png pdf	Table 1: Ranges of typical values for different sources of systematic uncertainty on the background estimates.
png pdf	Table 2: Ranges of typical values for different sources of systematic uncertainty on the signal yields.
png pdf	Table 3: Definitions of aggregate signal regions. Each region is obtained by selecting all events that pass the logical OR of the listed selections.
png pdf	Table 4: Post-fit predictions and observations for the aggregated regions defined in Table 3, together with the observed 95% CL limit on the number of signal events contributing to each region ($N_{95}^{\mathrm {obs}}$). A signal efficiency uncertainty of either 15 or 30% is assumed for calculating the limits.
png pdf	Table 5: Pre-fit predictions and observations for the aggregated regions defined in Table 3, together with the observed 95% CL limit on the number of signal events contributing to each region ($N_{95}^{\mathrm {obs}}$). A signal efficiency uncertainty of either 15 or 30% is assumed for calculating the limits.
png pdf	Table 6: Expected upper limits on the cross section of different simplified models, as determined from the full analysis, are compared to the upper limits obtained using only the aggregate signal region with the best sensitivity to each considered signal model. A 15% uncertainty in the signal selection efficiency is assumed for calculating these limits. The signal yields expected for an integrated luminosity of 2.3 fb are also shown.

Summary

This note presents the results of a search for new physics using events with one soft lepton and large $E_{\mathrm{T}}^{\text{miss}}$, inclusive in jet flavor and multiplicity. Results are based on a 2.3 fb$^{-1}$ data sample of $\sqrt{s}=$ 13 TeV proton-proton collisions collected with the CMS detector. No significant deviations from the standard model expectations are observed, and the results are used to set limits on models featuring compressed spectra. For pair production of top squarks decaying into four bodies, $\widetilde{t} \rightarrow b \widetilde\chi^{0} l (q) \nu (q^\prime)$, top squark masses below 340 GeV are excluded for $m_{\widetilde{t}} - m_{\widetilde\chi^{0}} =$ 50 GeV. For gluino pair production decaying to $\widetilde{g} \rightarrow q\bar{q} \widetilde\chi^{\pm}$ followed by $\widetilde\chi^{\pm} \rightarrow W^{*} \widetilde\chi^{0}$, with $m_{\widetilde\chi^{\pm}} - m_{\widetilde\chi^{0}} = $ 20 GeV, gluino masses in the range 900-1200 GeV are excluded for $\widetilde\chi^{0}$ masses in the range 100-800 GeV.

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