Inclusive search for squarks and gluinos in $pp$ collisions at $\sqrt{s}\mathbf{=}7\mathrm{TeV}$

A search is performed for heavy particle pairs produced in $\sqrt{s}=7\mathrm{TeV}$ proton-proton collisions with $35{\mathrm{pb}}^{-1}$ of data collected by the CMS experiment at the LHC. The search is sensitive to squarks and gluinos of generic supersymmetry models, provided they are kinematically accessible, with minimal assumptions on properties of the lightest superpartner particle. The kinematic consistency of the selected events is tested against the hypothesis of heavy particle pair production using the dimensionless razor variable $R$, related to the missing transverse energy $E_{\mathrm{T}}^{\mathrm{miss}}$. The new physics signal is characterized by a broad peak in the distribution of $M_R$, an event-by-event indicator of the heavy particle mass scale. This new approach is complementary to $E_{\mathrm{T}}^{\mathrm{miss}}$-based searches. After background modeling based on data, and background rejection based on $R$ and $M_R$, no significant excess of events is found beyond the standard model expectations. The results are interpreted in the context of the constrained minimal supersymmetric standard model as well as two simplified supersymmetry models.

Figure 1

Example of the $R$ frame reconstruction for the simulated production of a pair of squarks in the SUSY benchmark model LM1 [43]: (top) Three reconstructed jets (green arrows) and the reconstructed $E_T^{\mathrm{miss}}$ (black arrow projected on the transverse plane). The lengths of the arrows correspond to the magnitudes of the reconstructed momenta, and the yellow line represents the beam axis. (middle) The $R$ frame view of the same event, with the three jets replaced by two megajets, obtained by a longitudinal boost from the lab frame. (bottom) The momenta of the original parent squarks as they appear in the actual CM frame (blue arrows) and in the $R$ frame (red arrows), which is an approximation to the CM frame. In this event the squark masses are 536 GeV, the $E_{\mathrm{T}}^{\mathrm{miss}}$ is 218 GeV, the $R$ frame boost factor is ${\beta }_R=0.62$, and the $p_T$ of the jets is 192, 151, and 57 GeV.

Figure 2

Scatter plot in the ($M_R$, $R$) plane for simulated events: (top left) QCD multijet, (top right) $W+\mathrm{\text{jets}}$, (bottom left) $t\overline{t}+\mathrm{\text{jets}}$, and (bottom right) the SUSY benchmark model LM1 [43] with $M_{\Delta }=597\mathrm{GeV}$. The yields are normalized to an integrated luminosity of $35{\mathrm{pb}}^{-1}$. The bin size is ($20\mathrm{GeV}\times 0.015$).

Figure 3

(left) $M_R$ distributions for different values of the $R$ threshold for data events in the QCD multijet control sample. Fits of the $M_R$ distribution to an exponential function and an asymmetric Gaussian at low $M_R$, are shown as dotted black curves. (right) The exponential slope $S$ from fits to the $M_R$ distribution, as a function of the square of the $R$ threshold for data events in the QCD control sample.

Figure 4

(left) $M_R$ distributions for different values of the $R$ threshold from data events selected in the MU (upper) and ELE (lower) boxes. Dotted curves show the results of fits using two independent exponential functions and an asymmetric Gaussian at low $M_R$. (right) The slope $S$ of the first exponential component as a function of the square of the $R$ threshold in the MU (upper) and ELE (lower) boxes. The dotted lines show the results of the fits to the form $S=a+b{R}^2$.

Figure 5

The $M_R$ distributions with $R>0.45$ in the ELE (left) and MU (right) boxes for data (points) and backgrounds (curves). The bands show the uncertainties of the background predictions.

Figure 6

The $M_R$ distributions with $R>0.5$ in the HAD box for data (points) and backgrounds (curves) on (top) linear and (bottom) logarithmic scales. The bands show the uncertainties of the background predictions. The corresponding distributions for SUSY benchmark models LM1 [43] with $M_{\Delta }=597\mathrm{GeV}$ and LM0 [14] with $M_{\Delta }=400\mathrm{GeV}$ are overlaid.

Figure 7

Observed (solid curve) and expected (dot-dashed curve) 95% C.L. limits in the ($m_0$, $m_{1/2}$) CMSSM plane with $\tan \beta =3$ (left column) and $\tan \beta =10$ (right column), $A_0=0$, $\mathrm{sgn}(\mu )=+1$ from the ELE/MU/HAD box selection (top to bottom) ($R>0.45$ for ELE/MU, 0.5 for HAD, $M_R>500\mathrm{GeV}$). The $\pm$ 1 standard deviation equivalent variations in the uncertainties are shown as a band around the expected limits.

Figure 8

Observed (solid curve) and expected (dot-dashed curve) 95% C.L. limits in the ($m_0$, $m_{1/2}$) CMSSM plane with $\tan \beta =50$, $A_0=0$, $\mathrm{sgn}(\mu )=+1$ from the ELE (left)/HAD (right) box selection ($R>0.45/0.5$ (ELE/HAD), $M_R>500\mathrm{GeV}$). The $\pm$ 1 standard deviation equivalent variations in the uncertainties are shown as a band around the expected limits.

Figure 9

Upper limits on two simplified models: di-squark production (top) resulting in a $2\mathrm{\text{−}}\mathrm{\text{jet}}+E_{\mathrm{T}}^{\mathrm{miss}}$ final state and di-gluino (lower) production resulting in a $4\mathrm{\text{−}}\mathrm{\text{jet}}+E_{\mathrm{T}}^{\mathrm{miss}}$ final state. The shade scale indicates the value of the cross section excluded at 95% C.L. for each value of $m_{\mathrm{LSP}}$ and $m_{\mathrm{gluino}}$ or $m_{\mathrm{squark}}$. The solid and dashed contours indicate the 95% C.L. limits assuming the NLO cross section and its variations up and down by a factor of 3.