Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using $4.7{\mathrm{fb}}^{\mathbf{-}1}$ of $\sqrt{s}\mathbf{=}7\mathrm{TeV}$ proton-proton collision data

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-$p_{\mathrm{T}}$ electrons or muons is presented. The data represent the complete sample recorded in 2011 by the ATLAS experiment in 7 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of $4.7{\mathrm{fb}}^{-1}$. No excess above the Standard Model background expectation is observed. Gluino masses below 860 GeV and squark masses below 1320 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino, for squark or gluino masses below 2 TeV, respectively. Squarks and gluinos with equal masses below 1410 GeV are excluded. In minimal supergravity/constrained minimal supersymmetric Standard Model models with $\tan \beta =10$, $A_0=0$ and $\mu >0$, squarks and gluinos of equal mass are excluded for masses below 1360 GeV. Constraints are also placed on the parameter space of supersymmetric models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.

Figure 1

Observed $m_{\mathrm{eff}}(\mathrm{incl}.)$ distribution for channel A. In the top panel, the histograms show the SM background expectations, both before (black open histogram) and after [medium (red) open histogram] use of a fit to scale the expectations to CR observations. This fit is applied to illustrate the $\mathrm{SR}+\mathrm{CR}$ fitting technique used in the main analysis. Before scaling, the MC simulation expectations are normalized to luminosity. The multijet background is estimated using the jet smearing method described in the text. After scaling, the $W+\mathrm{\text{jets}}$, $Z+\mathrm{\text{jets}}$ and $t\overline{t}$ and single top quark and multijet distributions (denoted by full histograms) are normalized to data in corresponding control regions over the full $m_{\mathrm{eff}}$ range. Two MSUGRA/CMSSM benchmark model points with $m_0=500\mathrm{GeV}$, $m_{1/2}=570\mathrm{GeV}$, $A_0=0$, $\tan \beta =10$ and $\mu >$ and with $m_0=2500\mathrm{GeV}$, $m_{1/2}=270\mathrm{GeV}$, $A_0=0$, $\tan \beta =10$ and $\mu >$, illustrating different topologies, are also shown. These points lie just beyond the reach of the previous analysis [17]. The arrows indicate the locations of the lower edges of the two signal regions. The bottom panel shows the fractional deviation of the data from the total unscaled background estimate (black points), together with the fractional deviation of the total scaled background estimate from the total unscaled background estimate [medium (red) line]. The light (yellow) band shows the combined experimental uncertainties on the unscaled background estimates from jet energy scale, jet energy resolution, the effect of pileup, the treatment of energy outside of reconstructed jets and MC simulation sample size. The medium (green) band includes also the total theoretical uncertainties.

Figure 2

Observed $m_{\mathrm{eff}}(\mathrm{incl}.)$ distribution for channel ${\mathrm{A}}^{\prime }$, as for Fig. 1.

Figure 3

Observed $m_{\mathrm{eff}}(\mathrm{incl}.)$ distribution for channel B, as for Fig. 1.

Figure 4

Observed $m_{\mathrm{eff}}(\mathrm{incl}.)$ distribution for channel C, as for Fig. 1.

Figure 5

Observed $m_{\mathrm{eff}}(\mathrm{incl}.)$ distribution for channel D, as for Fig. 1.

Figure 6

Observed $m_{\mathrm{eff}}(\mathrm{incl}.)$ distribution for channel E, as for Fig. 1.

Figure 7

Leading photon $p_{\mathrm{T}}$ distribution from data and MC simulation (a) directly after the photon selection and (b) in CR1a for SR-A medium that requires $m_{\mathrm{eff}}>1400\mathrm{GeV}$. The bottom panel shows the ratio of data to MC expectation, with the light (yellow) band indicating the uncertainty.

Figure 8

Distributions of $R_2$ in four bins (a–d) of $|\eta |$ of the poorly reconstructed jet, for estimated true jet $p_{\mathrm{T}}$, defined as $|{\overrightarrow{p}}_{\mathrm{T}}^J+\overrightarrow{P}_{\mathrm{T}}{}^{\mathrm{miss}}|$, greater than 100 GeV. The black points represent collision data while the open medium (red) histogram represents the combined prediction. The jet smearing method described in the text is used to estimate the multijet contribution (referred to in the plots as pseudodata) while MC simulation predictions are used for the other background components. The lower panels show the fractional deviation of the data from the prediction (black points), with the light (yellow) bands showing the multijet uncertainty combined with the MC simulation statistical uncertainty on the nonmultijet estimate.

Figure 9

Comparison of observed and predicted distributions of $\Delta \varphi ({\mathrm{jet}}_i,\overrightarrow{P}_{\mathrm{T}}{}^{\mathrm{miss}}{)}_{\min }$ for the leading three jets [$\Delta \varphi ({\mathrm{jet}}_i,\overrightarrow{P}_{\mathrm{T}}{}^{\mathrm{miss}}{)}_{\min }$ $(i=\{1,2,3\})$], (a) after all selections except for those on $\Delta \varphi ({\mathrm{jet}}_i,\overrightarrow{P}_{\mathrm{T}}{}^{\mathrm{miss}}{)}_{\min }$, $m_{\mathrm{eff}}$ and $E_{\mathrm{T}}^{\mathrm{miss}}/m_{\mathrm{eff}}$ and (b) after all selections except for that on $\Delta \varphi ({\mathrm{jet}}_i,\overrightarrow{P}_{\mathrm{T}}{}^{\mathrm{miss}}{)}_{\min }$ for signal region C loose. The histograms show the MC simulation estimates of each background component. The medium (maroon) triangles show the multijet estimates from the jet smearing technique, normalized in the regions with $\Delta \varphi ({\mathrm{jet}}_i,\overrightarrow{P}_{\mathrm{T}}{}^{\mathrm{miss}}{)}_{\min }$ $(i=\{1,2,3\})<0.2\mathrm{rad}$, which replaces the multijet MC simulation estimate (denoted with a histogram) in the main analysis. The hatched region denotes the total uncertainty on the multijet estimate including statistical uncertainties from the seed event sample and the smearing procedure, systematic uncertainties in the jet response function, and bias in the seed event selection. The lower panels show the fractional deviation of the data from the prediction (black points), with the light (yellow) bands showing the multijet uncertainty combined with the MC simulation statistical uncertainty on the nonmultijet estimate.

Figure 10

The 95% ${\mathrm{CL}}_{\mathrm{s}}$ exclusion limits on (a) the ($m_{\tilde{g}}$, $m_{\tilde{q}}$) plane in a simplified MSSM scenario with only strong production of gluinos and first- and second-generation squarks, with direct decays to jets and neutralinos; (b) the ($m_0$, $m_{1/2}$) plane of MSUGRA/CMSSM for $\tan \beta =10$, $A_0=0$ and $\mu >0$. Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point. The black dashed lines show the expected limits, with the light (yellow) bands indicating the $1\sigma$ excursions due to experimental uncertainties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted lines are obtained by varying the cross section by the theoretical scale and PDF uncertainties. Previous results from ATLAS [17] are represented by the shaded region (blue) at bottom left in each case. The region excluded by chargino searches at LEP is taken from Ref. [71].

Figure 11

The 95% ${\mathrm{CL}}_{\mathrm{s}}$ exclusion limits on the ($m_{\tilde{g}}$, $m_{\tilde{q}}$) plane in MSSM models with nonzero neutralino masses. Combined observed exclusion limits are based on the best expected ${\mathrm{CL}}_{\mathrm{s}}$ per grid point as for Fig. 10, but with an LSP mass of (a) 195 and (b) 395 GeV. Curves are as defined in Fig. 10. The letters overlaid on the plot show the SR that contributes the best sensitivity at each point. Previous results from ATLAS [17] are represented by the shaded region (blue) at bottom left in each case.

Figure 12

The 95% ${\mathrm{CL}}_{\mathrm{s}}$ exclusion limits on simplified models assuming direct production of (a) gluino pairs with decoupled squarks or (b) squark pairs with decoupled gluinos, each decaying to two jets, or one jet, respectively, and a neutralino LSP. 95% Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point. The black dashed lines show the expected limits, with the light (yellow) bands indicating the $1\sigma$ excursions due to experimental uncertainties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted lines are obtained by varying the cross section by the theoretical scale and PDF uncertainties. The 95% ${\mathrm{CL}}_{\mathrm{s}}$ upper limit on the cross section times branching ratio (in fb) is printed for each model point.

Figure 13

Combined 95% ${\mathrm{CL}}_{\mathrm{s}}$ exclusion limits on simplified models assuming direct production of gluino pairs, each decaying via an intermediate chargino to two jets, a $W$ boson and a neutralino LSP. The chargino mass is fixed halfway in between the gluino and LSP masses in figure (a). The neutralino mass is fixed at 60 GeV in figure (b), where the $y$ axis shows the ratio of the chargino-LSP mass splitting to the gluino-LSP mass splitting. The black dashed lines show the expected limits, with the light (yellow) bands indicating the $1\sigma$ excursions due to experimental uncertainties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted lines are obtained by varying the cross section by the theoretical scale and PDF uncertainties. The 95% ${\mathrm{CL}}_{\mathrm{s}}$ upper limit on the cross section times branching ratio (in fb) is printed for each model point.

Figure 14

Combined 95% ${\mathrm{CL}}_{\mathrm{s}}$ exclusion limits on simplified models assuming direct production of left-handed squark-antisquark pairs, each decaying via an intermediate chargino to two jets, a $W$ boson and a neutralino LSP. The chargino mass is fixed halfway in between the squark and LSP masses in figure (a). In figure (b) the neutralino mass is fixed at 60 GeV; the $y$ axis shows the ratio of the chargino-LSP mass splitting to the squark-LSP mass splitting. The black dashed lines show the expected limits, with the light (yellow) bands indicating the $1\sigma$ excursions due to experimental uncertainties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted lines are obtained by varying the cross section by the theoretical scale and PDF uncertainties. The 95% ${\mathrm{CL}}_{\mathrm{s}}$ upper limit on the cross section times branching ratio (in fb) is printed for each model point.

Figure 15

Combined 95% ${\mathrm{CL}}_{\mathrm{s}}$ exclusion limits for the compressed SUSY models discussed in the text. In figure (a) all squarks, electroweak gauginos and the gluino are kinematically accessible. In figure (b) neutralinos (apart from the LSP) and charginos are decoupled. In figure (c) squarks are decoupled. The black dashed lines show the expected limits, with the light (yellow) bands indicating the $1\sigma$ excursions due to experimental uncertainties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted lines are obtained by varying the cross section by the theoretical scale and PDF uncertainties. The letters overlaid on the plot show the SR that contributes the best sensitivity at each point.