Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions

TL;DR

This ATLAS paper reports a search for supersymmetric squarks and gluinos in fully hadronic final states with jets and missing transverse momentum, using 1.04 fb⁻¹ of 7 TeV LHC data. The analysis employs a multi-region signal strategy with five SRs and a data-driven, likelihood-based background estimation from control regions, achieving robust background constraints. No evidence of SUSY is found, and the study sets stringent 95% CL exclusions on gluino and squark masses, extending prior experimental bounds, including MSUGRA/CMSSM scenarios. The work demonstrates the power of high-multiplicity jet selections and cross-region background fitting in probing SUSY parameter space at the LHC’s early 7 TeV run.

Abstract

A search for squarks and gluinos in events containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2011 by the ATLAS experiment in sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation is observed in 1.04 fb^-1 of data. Gluino and squark masses below 700 GeV and 875 GeV respectively 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. The exclusion limit increases to 1075 GeV for squarks and gluinos of equal mass. In MSUGRA/CMSSM models with tan(beta)=10, A_0=0 and mu> 0, squarks and gluinos of equal mass are excluded for masses below 950 GeV. These limits extend the region of supersymmetric parameter space excluded by previous measurements.

Figures (2)

• Figure 1: The observed $m_{\mathrm{eff}}$ distributions in the signal regions for the $\ge 2$ jet channel (top left), the $\ge 3$ jet channel (top right) and the two $\ge 4$ jet channels (bottom left), and for the high mass channel using the inclusive definition of $m_{\mathrm{eff}}$ (bottom right), after all the selection criteria but the $m_{\mathrm{eff}}$ cut. These plots also show the expected SM contributions obtained from MC simulated samples prior to normalisation using the data-driven likelihood method described in the text. The red arrows indicate the lower bounds on $m_{\mathrm{eff}}$ used in the final signal region selections. The expectation for a MSUGRA/CMSSM reference point with $m_0=660$Ge V, $m_{1/2}=240$Ge V, $A_0=0$, $\tan\beta=10$ and $\mu> 0$ is also shown. This reference point is also indicated by the star on Figure \ref{['fig:limitcombinedCLs']}. Below each plot the ratio of the data to the SM expectation is provided. Black vertical bars show the statistical uncertainty from the data, while the yellow band shows the size of the systematic uncertainties from the MC simulation.
• Figure 2: Combined exclusion limits for simplified SUSY models with $m(\hbox{$\tilde{\chi}^0_1$})=0$ (left) and MSUGRA/CMSSM models with $\tan\beta=10$, $A_0=0$ and $\mu>0$ (right). The combined limits are obtained by using the signal region which generates the best expected limit at each point in the parameter plane. The dashed-blue line corresponds to the median expected 95% C.L. limit and the red line corresponds to the observed limit at 95% C.L. The dotted blue lines correspond to the $\pm1\sigma$ variation in the expected limits. Also shown for comparison purposes in the figures are limits from the Tevatron Abachi:1995ngAffolder:2001tcAaltonen:2008rv:2007ww and LEP Abdallah:2003xeAchard:2003ge , although it should be noted that some of these limits were generated with different models or parameter choices (see legends). The previous published ATLAS limits from this analysis daCosta:2011qk are also shown. The MSUGRA/CMSSM reference point used in Figure \ref{['fig:meff_data']} is indicated by the star in the right-hand figure.