Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using 4.7 fb^-1 of sqrt(s) = 7 TeV proton-proton collision data

TL;DR

This ATLAS paper searches for supersymmetry in final states with jets and missing transverse momentum, vetoing high-pT leptons, using 4.7 fb^-1 of 7 TeV proton-proton collisions. It employs six signal channels with an $m_{ m eff}$-based strategy and data-driven transfer factors from multiple control regions to estimate SM backgrounds, including $Z$+jets, $W$+jets, ttbar, and multi-jet processes. No excess above the SM expectation is observed, and the results set new 95% CL exclusions in simplified MSSM and MSUGRA/CMSSM parameter spaces, extending previous ATLAS bounds and constraining compressed SUSY scenarios. The analysis demonstrates robust background modeling via gamma+jets and Z->ll control regions, jet-smearing techniques, and a global likelihood fit that coherently propagates systematic uncertainties into the limits.

Abstract

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-pT 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 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 MSUGRA/CMSSM 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 SUSY models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.

Figures (15)

• Figure 1: Observed $m_{\mathrm{eff}}({\rm incl.})$ 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 SR+CR fitting technique used in the main analysis. Before scaling, the MC simulation expectations are normalized to luminosity. The multi-jet background is estimated using the jet smearing method described in the text. After scaling, the $W$+jets, $Z$+jets and $t\bar{t}$ and single top quark and multi-jet 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 $m_{\rm 0}$=500 Ge V, $m_{\rm 1/2}$=570 GeV, $A_{\rm 0}$=0, $\tan\beta$=10 and $\mu>$ 0 and with $m_{\rm 0}$=2500 Ge V, $m_{\rm 1/2}$=270 GeV, $A_{\rm 0}$=0, $\tan\beta$=10 and $\mu>$ 0, illustrating different topologies, are also shown. These points lie just beyond the reach of the previous analysis Aad:2011ib. 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 pile-up, 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 $m_{\mathrm{eff}}({\rm incl.})$ distribution for channel A$'$, as for Fig. \ref{['fig:sra']}.
• Figure 3: Observed $m_{\mathrm{eff}}({\rm incl.})$ distribution for channel B, as for Fig. \ref{['fig:sra']}.
• Figure 4: Observed $m_{\mathrm{eff}}({\rm incl.})$ distribution for channel C, as for Fig. \ref{['fig:sra']}.
• Figure 5: Observed $m_{\mathrm{eff}}({\rm incl.})$ distribution for channel D, as for Fig. \ref{['fig:sra']}.