Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using sqrt(s)=7 TeV pp collisions with the ATLAS detector

TL;DR

This ATLAS analysis searches for new TeV-scale states decaying to high jet multiplicities in association with missing transverse momentum, using 1.34 fb$^{-1}$ of 7 TeV pp collision data. Backgrounds are constrained with data-driven methods in high-multiplicity regions, with leptonic components guided by MC transfer factors and cross-checked against jet-smearing. No deviation from the Standard Model is observed, and results are interpreted within the MSUGRA/CMSSM framework to set limits on gluino and squark masses, extending previous ATLAS constraints. The work demonstrates the viability of data-driven techniques for challenging high-$N_{ m jet}$ final states and provides important constraints on SUSY scenarios with rich jet cascades.

Abstract

Results are presented of a search for any particle(s) decaying to six or more jets in association with missing transverse momentum. The search is performed using 1.34 fb^-1 of sqrt(s)=7 TeV proton-proton collisions recorded by the ATLAS detector during 2011. Data-driven techniques are used to determine the backgrounds in kinematic regions that require at least six, seven or eight jets, well beyond the multiplicities required in previous analyses. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a supersymmetry model (MSUGRA/CMSSM) where they extend previous constraints.

Figures (5)

• Figure 1: The distribution of the variable $E_{\mathrm{T}}^{\mathrm{miss}}{}/\sqrt{H_T}\,$ for control regions requiring (\ref{['h5j30_MetSig6']}) exactly six jets with $p_{\mathrm{T}}>55\,\mathrm{\ Ge V} \textrm{Ge V}$ or (\ref{['h4j45_MetSig5']}) exactly five jets with $p_{\mathrm{T}}>80\,\mathrm{\ Ge V} \textrm{Ge V}$. Overlaid are templates taken from selections requiring (\ref{['h5j30_MetSig6']}) exactly five jets with $p_{\mathrm{T}}>55\,\mathrm{\ Ge V} \textrm{Ge V}$ or (\ref{['h4j45_MetSig5']}) exactly four jets with $p_{\mathrm{T}}>80\,\mathrm{\ Ge V} \textrm{Ge V}$. These templates are normalised to the data in the region with $E_{\mathrm{T}}^{\mathrm{miss}}{}/\sqrt{H_T}<1.5$. The background estimation includes the ALPGEN Monte-Carlo prediction for the 'leptonic' Standard Model backgrounds. For illustrative purposes the plots also contain the distribution expected for an example MSUGRA/CMSSM point with $m_0=1220$Ge V and $m_{1/2}=180$Ge V. In all ratio plots (lower), in regions with very low numbers of events, some points may lie off the shown range and for bins with no observed events no ratio is shown. For $t\bar{t}$ backgrounds the labels 'qq' and 'ql,ll' represent fully hadronic and non-fully-hadronic decays respectively.
• Figure 2: Observed and predicted jet multiplicity distributions for jets with $p_{\mathrm{T}}{}>55$ GeV (upper) and with $p_{\mathrm{T}}{}>80$ GeV (lower) in four example control regions defined by $1.5\,{\mathrm{\ Ge V} \textrm{Ge V}^{1/2}}<{{ E_{\mathrm{T}}^{\mathrm{miss}}}/\sqrt{{H_{\rm T}}}}<2\,{\mathrm{\ Ge V} \textrm{Ge V}^{1/2}}$ (left) and $2\,{\mathrm{\ Ge V} \textrm{Ge V}^{1/2}}<{{ E_{\mathrm{T}}^{\mathrm{miss}}}/\sqrt{{H_{\rm T}}}}<3\,{\mathrm{\ Ge V} \textrm{Ge V}^{1/2}}$ (right). Overlaid are templates taken from selections requiring ${{ E_{\mathrm{T}}^{\mathrm{miss}}}/\sqrt{{H_{\rm T}}}}<1.5\,{\mathrm{\ Ge V} \textrm{Ge V}^{1/2}}\,$ which are normalised to the data in the lowest jet multiplicity bin shown. The background estimation includes the ALPGEN Monte-Carlo prediction for the 'leptonic' Standard Model backgrounds. For illustrative purposes the plots also contain the distribution expected for an example MSUGRA/CMSSM point with $m_0=1220$Ge V and $m_{1/2}=180$Ge V.
• Figure 3: The multiplicity of jets with $p_{\mathrm{T}}>55\,\mathrm{\ Ge V} \textrm{Ge V}{}$ (left) or $p_{\mathrm{T}}>80\,\mathrm{\ Ge V} \textrm{Ge V}{}$ (right) for events in various control regions. Top row: top-quark enhanced control regions requiring at least one $b$-tagged jet, a single isolated muon with $p_T>20\,$GeV and $|\eta|<2.4$ and $40<m_{\rm T}<100\,$GeV. Middle row: $W$-boson enhanced region (as for top, but with $b$-jet veto). Bottom row: $Z\rightarrow \mu\mu$ enhanced region.
• Figure 4: The distribution of the variable $E_{\mathrm{T}}^{\mathrm{miss}}{}/\sqrt{H_T}\,$ for events with (\ref{['fig:metsig:7j55']}) seven or more jets with $p_{\mathrm{T}}>55\,\mathrm{\ Ge V} \textrm{Ge V}$ or (\ref{['fig:metsig:6j80']}) six or more jets with $p_{\mathrm{T}}>80\,\mathrm{\ Ge V} \textrm{Ge V}$. Overlaid are the hadronic background templates plus the ALPGEN Monte-Carlo prediction for the 'leptonic' Standard Model backgrounds. For illustrative purposes the plots also contain the distribution expected for an example MSUGRA/CMSSM point with $m_0=1220$Ge V and $m_{1/2}=180$Ge V.
• Figure 5: Combined exclusion bounds in the $\tan\beta=10, A_0=0, \mu>0$ slice of the MSUGRA/CMSSM space. Gluinos with masses below 520 GeV, and gluinos with masses below 680 GeV under the assumption that $m_{\rm squark} = 2 \times m_{\rm gluino}$ are excluded at the 95% confidence level. Limits from individual SRs can be found elsewhere multijet_2011_auxiliary. Recent limits from ATLAS ATLAS-ZERO-LEPTON-2011, as well as previous limits from D0 and CDF Abachi:1995ng*Affolder:2001tc*Aaltonen:2008rv*:2007ww and LEP lepsusy are also shown.