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\section{Introduction}
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\label{sec:intro}
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In this paper we describe a search for physics beyond the standard model (BSM)
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in a sample of proton-proton collisions at a centre-of-mass energy of 7~TeV.
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The data sample was collected with the Compact Muon Solenoid (CMS) detector~\cite{JINST} at
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the Large Hadron Collider (LHC) in 2011
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and corresponds to an integrated luminosity of \lumifinal.
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This is an update of a previous analysis performed with a data sample of 34~pb$^{-1}$
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collected in 2010~\cite{ref:ospaper}.
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The BSM signature in this search is motivated by three general considerations.
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First, new particles predicted by BSM
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physics scenarios are expected to be heavy, since they have so far eluded detection.
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Second, BSM physics signals with high
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enough cross sections to be observed in our current dataset are expected to be
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produced strongly, resulting in significant hadronic activity.
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Third, astrophysical evidence for
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dark matter suggests~\cite{ref:DM,ref:DM2} that the mass of weakly-interacting
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massive particles is of the order of the electroweak symmetry breaking
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scale. Such particles, if produced in pp collisions, could escape detection and give rise to
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an apparent imbalance in the event transverse energy. We therefore focus on the
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region of high missing transverse energy (\MET). An example of a specific BSM scenario is
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provided by R-parity conserving supersymmetric (SUSY) models in which
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new, heavy particles are pair-produced and subsequently undergo
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cascade decays, producing hadronic jets and
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leptons~\cite{Martin:fk,susy1,susy2,susy3,susy4,susy5,susy6}.
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These cascade decays may terminate in the
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production of weakly-interacting massive particles, resulting in large \MET.
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The results reported in this paper are part of a broad program of BSM searches
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in events with jets and \MET, characterized by the number and
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type of leptons in the final state.
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Here we describe a search for events containing opposite-sign isolated
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lepton pairs ($e^+e^-$, $e^{\pm}\mu^{\mp}$, $\mu^+\mu^-$) in addition to the jets
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and \MET. Results from complementary searches with different final states have
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already been reported in Ref.~\cite{ref:RA1} {\bf ADD MORE REFS HERE}.
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Our analysis strategy is as follows. In order to select dilepton events, we
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use high-\pt\ dilepton triggers and a preselection based
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on that of the $t\bar{t}$ cross section measurement in the dilepton channel~\cite{ref:top}.
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%, which used a data sample corresponding to an integrated luminosity of 3.1\pbinv.
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Good agreement is found between this
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data sample and predictions from SM Monte Carlo (MC) simulations in terms of the event yields
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and shapes of various kinematic distributions.
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We search for a kinematic edge in the dilepton mass distribution, which is a characteristic
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feature of SUSY models in which the opposite-sign leptons are produced via the decay
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$\chi_2^0 \to \chi_1^0 \ell^+\ell^-$.
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Because BSM physics is expected to have large hadronic activity and \MET\ as discussed
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above, we proceed to define 2 signal regions
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with requirements on these quantities to select about 0.1\%
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of dilepton $t\bar{t}$ events, as predicted by MC.
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The observed event yields in the signal regions are compared with the predictions from two
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independent background estimation techniques based on data control samples,
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as well as with SM and BSM MC expectations.
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%The search is not optimized in the context of any particular BSM physics, e.g. specific SUSY model.
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No specific BSM physics scenario, e.g.\ a particular SUSY model, has been used to optimize the search.
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In order to illustrate the sensitivity of the search, a simplified and practical model of
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SUSY breaking, the constrained minimal supersymmetric
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extension of the standard model (CMSSM)~\cite{CMSSM,CMSSM2}, is used. The CMSSM is described by
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five parameters: the universal scalar and gaugino mass parameters ($m_0$ and $m_{1/2}$, respectively),
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the universal trilinear soft SUSY breaking parameter $A_0$, the
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ratio of the vacuum expectation values of the two Higgs doublets ($\tan\beta$), and the sign of the
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Higgs mixing parameter $\mu$.
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Throughout the paper, two CMSSM parameter sets, referred
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to as LM1 and LM3~\cite{TDR}, are used to illustrate possible CMSSM yields. The parameter values
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defining LM1 (LM3) are $m_0 = 60~(330) \GeVcc$, $m_{1/2} = 250~(240) \GeVcc$, $\tan\beta = 10~(20)\GeV$;
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both LM1 and LM3 have $A_0 = 0$ and $\mu > 0$. These two scenarios are beyond the exclusion reach
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of previous searches performed at the Tevatron and LEP. The LM1 scenario was recently excluded
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by a search performed at CMS in events with jets and \MET~\cite{ref:RA1}.
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In this analysis, the LM1 and LM3 scenarios serve as benchmarks which
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may be used to allow comparison of the sensitivity with other analyses.
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%In the Standard Model (SM), the main sources of isolated dileptons are Drell-Yan production
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%($q\bar q$ annihilation into a virtual photon or a $Z$) and $t\bar{t}$ production.
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%In this search we exclude lepton pairs with invariant mass consistent with a $Z$ boson,
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%leaving $t\bar{t}$ as the dominant SM background. A separate search for BSM physics in the
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%$Z+\textrm{jets}$ sample will be described in a forthcoming paper.
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