Search for supersymmetry in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ in final states with missing transverse momentum and $b$-jets with the ATLAS detector

The results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to $2.05{\mathrm{fb}}^{-1}$ of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ recorded with the ATLAS detector at the Large Hadron Collider are reported. No significant excess is observed with respect to the prediction for standard model processes. Results are interpreted in a variety of $R$-parity conserving models in which scalar bottoms and tops are the only scalar quarks to appear in the gluino decay cascade, and in an SO(10) model framework. Gluino masses up to 600–900 GeV are excluded, depending on the model considered.

Figure 1

Distribution of the effective mass (top) and $E_{\mathrm{T}}^{\mathrm{miss}}$ (bottom) in the CR0-1 control region for the 1-electron (left) and 1-muon (right) channels. The color labeled “others” includes contributions from $Z$, diboson, and multijet production processes. The hatched band shows the systematic uncertainty, which includes both experimental uncertainties (among which JES and $b$-tagging uncertainties are dominant) and theoretical uncertainties on the background normalization and shape. The small insets show the ratio between the observed distribution and that predicted for the standard model background. Although the distributions are presented separately for $e$ and $\mu$, the background estimation uses the sum of the $e$ and $\mu$ yields in the CR0.

Figure 2

Distribution of the effective mass (top) and $E_{\mathrm{T}}^{\mathrm{miss}}$ (bottom) in the CR0-2 control region for the 1-electron (left) and 1-muon (right) channels. The hatched band shows the systematic uncertainty, which includes both experimental uncertainties (among which JES and $b$-tagging uncertainties are dominant) and theoretical uncertainties on the background normalization and shape. The small insets show the ratio between the observed distribution and that predicted for the standard model background. Although the distributions are presented separately for $e$ and $\mu$, the background estimation uses the sum of the $e$ and $\mu$ yields in the CR0.

Figure 3

Distribution of the effective mass (top) and $E_{\mathrm{T}}^{\mathrm{miss}}$ (bottom) in the CR1 control region for the 1-electron (left) and 1-muon (right) channels. The color labeled others includes contributions from $Z$, diboson, and multijet production processes. The hatched band shows the systematic uncertainty, which includes both experimental uncertainties (among which JES and $b$-tagging uncertainties are dominant) and theoretical uncertainties on the background normalization and shape. The small insets show the ratio between the observed distribution and that predicted for the standard model background.

Figure 4

Distribution of the effective mass (top) and $E_{\mathrm{T}}^{\mathrm{miss}}$ (bottom) in SR0-A1 (left) and SR0-A2 (right). The hatched band shows the systematic uncertainty, which includes both experimental uncertainties (among which JES and $b$-tagging uncertainties are dominant) and theoretical uncertainties on the background normalization and shape. The small insets show the ratio between the observed distribution and that predicted for the standard model background.

Figure 5

Distribution of the effective mass (top) and $E_{\mathrm{T}}^{\mathrm{miss}}$ (bottom) for the 1-electron (left) and 1-muon (right) channel in SR1-D. The color labeled “others” includes contributions from $Z$, diboson, and multijet production processes. The hatched band shows the systematic uncertainty, which includes both experimental uncertainties (among which JES and $b$-tagging uncertainties are dominant) and theoretical uncertainties on the background normalization and shape. The small insets show the ratio between the observed distribution and that predicted for the standard model background.

Figure 6

Observed and expected 95% CL exclusion limits in the ($m_{\tilde{g}}$, $m_{{\tilde{b}}_1}$) plane (gluino-sbottom models). For each scenario, the signal region providing the best expected limit is chosen. The neutralino mass is assumed to be 60 GeV and the NLO cross sections are calculated using PROSPINO. The result is compared to previous results from ATLAS [21] and CDF [69] searches which assume the same gluino-sbottom decays hypotheses. Exclusion limits from the CDF [70], D0 [71], and ATLAS [23] experiments on direct sbottom pair production are also shown.

Figure 7

Observed and expected 95% CL exclusion limits in the ($m_{\tilde{g}}$, $m_{{\tilde{\chi }}_1^0}$) plane (Gbb models). For each scenario, the signal region selection providing the best expected limit is chosen.

Figure 8

The observed and expected 95% CL exclusion limits in the ($m_{\tilde{g}}$, $m_{{\tilde{t}}_1}$) plane (gluino-stop models) using the best expected limit between SR1-D and SR1-E for each signal point. The result is compared to previous results from ATLAS [21] searches which assume the same gluino-stop decays hypotheses.

Figure 9

The observed and expected 95% CL exclusion limits in the ($m_{\tilde{g}}$, $m_{{\tilde{\chi }}_1^0}$) plane (Gtt) using the best expected limit between SR1-D and SR1-E for each signal point. The observed and expected 95% CL exclusion limits in the ($m_{\tilde{g}}$, $m_{{\tilde{\chi }}_1^0}$) plane (Gtb models) using the best expected limit between SR1-D and SR1-E for each signal point.

Figure 10

The observed and expected 95% CL exclusion limits in the ($m_{\tilde{g}}$, $m_{{\tilde{\chi }}_1^0}$) plane (Gtb models) using the best expected limit between SR1-D and SR1-E for each signal point.

Figure 11

Cross sections as a function of the gluino mass for DR3 (a) and HS (b) models. The observed and expected 95% CL exclusion limits are shown, respectively, by red solid and blue dotted lines. For each gluino mass, the signal region yielding the best expected limit is used. The NLO theoretical cross section from PROSPINO is shown in black. Previous limits obtained by ATLAS [21] with $\mathcal{L}=35{\mathrm{pb}}^{-1}$ are superimposed for reference.