Search for supersymmetry in events with one lepton and multiple jets in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

A search for supersymmetry is performed in events with a single electron or muon in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of $2.3{\mathrm{fb}}^{-1}$. Several exclusive search regions are defined based on the number of jets and $b$-tagged jets, the scalar sum of the jet transverse momenta, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. The observed event yields in data are consistent with the expected backgrounds from standard model processes. The results are interpreted using two simplified models of supersymmetric particle spectra, both of which describe gluino pair production. In the first model, each gluino decays via a three-body process to top quarks and a neutralino, which is associated with the observed missing transverse momentum in the event. Gluinos with masses up to 1.6 TeV are excluded for neutralino masses below 600 GeV. In the second model, each gluino decays via a three-body process to two light quarks and a chargino, which subsequently decays to a $W$ boson and a neutralino. The mass of the chargino is taken to be midway between the gluino and neutralino masses. In this model, gluinos with masses below 1.4 TeV are excluded for neutralino masses below 700 GeV.

Figure 1

Diagrams showing the simplified models (left) T1tttt and (right) T5qqqqWW. Depending on the mass difference between the chargino (${\tilde{\chi }}_1^{\pm }$) and the neutralino (${\tilde{\chi }}_1^0$), the $W$ boson can be virtual.

Figure 2

The $H_{\mathrm{T}}$ distribution for (left) the multi-$b$ analysis and (right) the zero-$b$ analysis, both after the baseline selection. The simulated background events are stacked on top of each other, and several signal points are overlaid for illustration, but without stacking. Overflows are included in the last bin. The label DY refers to $q\overline{q}\to \mathrm{Z}/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}$ events, and QCD refers to multijet events. The event yields for the benchmark models have been scaled up by a factor of 10. The ratio of data to simulation is given below each of the panels. All uncertainties are statistical only.

Figure 3

Comparison of the $\mathrm{\Delta }\mathrm{\Phi }$ distribution for (left) the multi-$b$ and (right) the zero-$b$ analysis after the baseline selection. The simulated background events are stacked on top of each other, and several signal points are overlaid for illustration, but without stacking. The wider bins are normalized to a bin width of 0.1. The label DY refers to $q\overline{q}\to \mathrm{Z}/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}$ events, and QCD refers to multijet events. The event yields for the benchmark models have been scaled up by a factor of 10. The ratio of data to simulation is given below each of the panels.

Figure 4

Fits to the $n_b$ multiplicity for control regions in (left) $3\le n_{\text{jet}}\le 4$ ($250\le L_{\mathrm{T}}<350\mathrm{GeV}$, $H_{\mathrm{T}}\ge 500\mathrm{GeV}$, $\mathrm{\Delta }\mathrm{\Phi }<1$) and (right) $6\le n_{\text{jet}}\le 7$ ($250\le L_{\mathrm{T}}<350\mathrm{GeV}$, $H_{\mathrm{T}}\ge 750\mathrm{GeV}$, $\mathrm{\Delta }\mathrm{\Phi }<1$) in data (muon channel). The solid lines represent the templates scaled according to the fit result (blue for $t\overline{t}+\mathrm{jets}$, green for $W+\mathrm{jets}$, turquoise for QCD, and red for the remaining backgrounds), the dashed line shows the sum after the fit, and the points with error bars represent data.

Figure 5

Multi-$b$ search: Comparison of observed and predicted background event yields in the 30 search regions. Upper panel: The data are shown by black points with error bars, while the total SM background predictions are shown by a grey line, with a hatched region representing its uncertainty. For illustration, the relative fraction of the different SM background contributions, as determined from simulation, is shown by the stacked, colored histograms, whose total normalization is set by the total background yields obtained from the control samples in the data. The expected event yields for two T1tttt SUSY benchmark models are shown by open histograms, each of which is shown stacked on the total background prediction. The vertical dashed and dotted lines separate different $n_{\text{jet}}$ and $L_{\mathrm{T}}$ bins, respectively, as indicated by the $x$-axis labels. Lower panel: The ratio of the yield observed in data to the predicted background yield is shown for each bin. The error bars on the data points indicate the combined statistical and systematic uncertainty in the ratio. The grey hatched region indicates the uncertainty on the ratio that arises from the uncertainty on the background prediction.

Figure 6

Zero-$b$ search: Observed and predicted event counts in the 13 search regions. Upper panel: The black points with error bars show the number of observed events. The filled, stacked histograms represent the predictions for $t\overline{t}+\mathrm{jets}$, $W+\mathrm{jets}$ events, and the remaining backgrounds. The uncertainty on the background prediction is shown as a grey hatched region. The expected yields from three T5qqqqWW model points, added to the SM background, are shown as solid lines. Lower panel: The ratio of the yield observed in data to the predicted background yield is shown for each bin. The error bars on the data points indicate the combined statistical and systematic uncertainty in the ratio. The grey hatched region indicates the uncertainty on the ratio that arises from the uncertainty on the background prediction.

Figure 7

Cross-section limits at a 95% C.L. for the (left) T1tttt and (right) T5qqqqWW models, as a function of the gluino and LSP masses. In T5qqqqWW, the pair-produced gluinos each decay to a quark-antiquark pair of the first or second generation ($q\overline{q}$), and a chargino (${\tilde{\chi }}_1^{\pm }$) with its mass taken to be $m_{{\tilde{\chi }}_1^{\pm }}=0.5(m_{\tilde{g}}+m_{{\tilde{\chi }}_1^0})$. The solid black (dashed red) lines correspond to the observed (expected) mass limits, with the thicker lines representing the central values and the thinner lines representing the $\pm 1\sigma$ uncertainty bands related to the theoretical (experimental) uncertainties.