Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton in $\sqrt{s}\mathbf{=}7\mathrm{TeV}$ pp collisions using $1{\mathrm{fb}}^{\mathbf{-}1}$ of ATLAS data

We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using $1.04{\mathrm{fb}}^{-1}$ of proton-proton collision data at $\sqrt{s}=7\mathrm{TeV}$ recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear $R$-parity violation.

Figure 1

Distributions after requiring one electron with $p_{\mathrm{T}}>25\mathrm{GeV}$ or one muon with $p_{\mathrm{T}}>20\mathrm{GeV}$, and at least three jets with $p_{\mathrm{T}}>60,25,25\mathrm{GeV}$ and $\Delta \varphi ({\mathrm{jet}}_i,{\overrightarrow{E}}_{\mathrm{T}}^{\mathrm{miss}})>0.2$. The top row shows the missing transverse momentum, $E_{\mathrm{T}}^{\mathrm{miss}}$, the middle row shows the transverse mass, $m_{\mathrm{T}}$, and the bottom row displays the effective mass, $m_{\mathrm{eff}}$. The electron channel is shown in the left column, the muon channel is shown in the right column. The “Data/SM” plots show the ratio between data and the summed standard model expectation. In these plots, the standard model expectation is derived from Monte Carlo simulations only, normalized to the theoretical cross sections. The uncertainty band on the standard model expectation combines the MC statistical uncertainty and systematic uncertainties on the jet energy scale and resolution, the lepton resolution and identification efficiencies, pileup and luminosity. For illustration, the expected signal distributions of the MSUGRA/CMSSM model point $m_0=500\mathrm{GeV}$, $m_{1/2}=330\mathrm{GeV}$ are also shown.

Figure 2

Distributions after requiring one electron with $p_{\mathrm{T}}>25\mathrm{GeV}$ or one muon with $p_{\mathrm{T}}>20\mathrm{GeV}$, and at least four jets with $p_{\mathrm{T}}>60,25,25,25\mathrm{GeV}$ and $\Delta \varphi ({\mathrm{jet}}_i,{\overrightarrow{E}}_{\mathrm{T}}^{\mathrm{miss}})>0.2$. The top row shows the missing transverse momentum, the middle row shows the transverse mass, and the bottom row displays the effective mass. The electron channel is shown in the left column, the muon channel is shown in the right column. The “Data/SM” plots show the ratio between data and the summed standard model expectation. In these plots, the standard model expectation is derived from Monte Carlo simulations only, normalized to the theoretical cross sections. The uncertainty band on the standard model expectation combines the MC statistical uncertainty and systematic uncertainties on the jet energy scale and resolution, the lepton resolution and identification efficiencies, pileup and luminosity. For illustration, the expected signal distributions of the MSUGRA/CMSSM model point $m_0=500\mathrm{GeV}$, $m_{1/2}=330\mathrm{GeV}$ are also shown.

Figure 3

Distributions for events in the lepton plus three jets control regions for the electron channel (left column) and muon channel (right column). Top row: effective mass in the $W+\mathrm{\text{jets}}$ control region. Middle row: effective mass in the top control region. Bottom row: number of $b$-tagged jets in the combined $W+\mathrm{\text{jets}}$ and top control regions. The “Data/SM” plots show the ratio between data and the summed standard model expectation. The uncertainty band on the standard model expectation combines the MC statistical uncertainty and systematic uncertainties on the jet energy scale and resolution, $b$-tagging, the lepton resolution and identification efficiencies, pileup and luminosity.

Figure 4

Distributions for events in the lepton plus four jets control regions for the electron channel (left column) and muon channel (right column). Top row: effective mass in the $W+\mathrm{\text{jets}}$ control region. Bottom row: effective mass in the top control region. The “Data/SM” plots show the ratio between data and the summed standard model expectation. The uncertainty band on the standard model expectation combines the MC statistical uncertainty and systematic uncertainties on the jet energy scale and resolution, $b$-tagging, the lepton resolution and identification efficiencies, pileup and luminosity.

Figure 5

Distributions of the effective mass for events in the 3-jet signal regions 3JL (top) and 3JT (bottom) for the electron channel (left) and the muon channel (right), after application of the final selection criteria described in Sec. 7a, except for the cut on $m_{\mathrm{eff}}$ itself. The “Data/SM” plots show the ratio between data and the summed standard model expectation. The uncertainty band on the standard model expectation combines the MC statistical uncertainty and systematic uncertainties on the jet energy scale and resolution, the lepton resolution and identification efficiencies, pileup and luminosity. For illustration, the expected signal distributions of the MSUGRA/CMSSM model point $m_0=500\mathrm{GeV}$, $m_{1/2}=330\mathrm{GeV}$ are also shown.

Figure 6

Distributions of the effective mass for events in the 4-jet signal regions 4JL (top) and 4JT (bottom) for the electron channel (left) and the muon channel (right), after application of the final selection criteria described in Sec. 7a, except for the cut on $m_{\mathrm{eff}}$ itself. The “Data/SM” plots show the ratio between data and the summed standard model expectation. The uncertainty band on the standard model expectation combines the MC statistical uncertainty and systematic uncertainties on the jet energy scale and resolution, the lepton resolution and identification efficiencies, pileup and luminosity. For illustration, the expected signal distributions of the MSUGRA/CMSSM model point $m_0=500\mathrm{GeV}$, $m_{1/2}=330\mathrm{GeV}$ are also shown.

Figure 7

Observed and expected 95% CL exclusion limits, as well as the $\pm 1\sigma$ variation on the median expected limit, in the combined electron and muon channels. The plots also show the published limits from CDF [60], D0 [61], and the results from the LEP experiments [62].

Figure 8

Excluded cross sections at 95% confidence level for the simplified models. The left column shows the results for the gluino models, the right column shows the results for the squark models. The top row plots represent the case $x=1/4$, the middle row $x=1/2$, and the bottom row $x=3/4$. The color coding (right axis) represents the model-independent cross section limit. Full lines indicate the observed exclusion regions in the shown plane assuming production cross sections as calculated with PROSPINO for the MSSM, and a 100% branching fraction into the assumed decay modes. The dashed line shows the corresponding median expected limit and the dotted lines show the $\pm 1\sigma$ variation on the expected limit.

Figure 9

Observed and expected 95% CL exclusion limits, as well as the $\pm 1\sigma$ variation on the expected limit, for the bilinear R-parity violation model in MSUGRA parameter space using the 4JT selection in the muon channel. The region with LSP lifetimes $c\tau >15\mathrm{mm}$ is not shown.