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\section{Event selection}
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\label{sec:eventSel}
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Events used in this search are required to contain one or two isolated
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leptons (electrons or muons). The triggers used
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require the presence of a $\pt>27$~GeV (24~GeV) electron (muon),
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or a pair of leptons (electrons or muons) with leading $\pt>17$~GeV
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and trailing $\pt>8$~GeV.
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Events are reconstructed offline using the particle-flow (PF)
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algorithm~\cite{PFT-10-004,PFT-08-001}, which provides a
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self-consistent global assignment of momenta and energies to the physics objects. Details of
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the reconstruction and identification procedures are given in
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Refs.~\cite{EGM-10-004,MUO-10-004} for electrons and muons.
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Jets are reconstructed with the anti-$k_{\mathrm{T}}$ clustering
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algorithm~\cite{Cacciari:2008gp} with a distance parameter of
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0.5. Corretions dependent on \pt\ and $\eta$ are applied to account for residual
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effects of non-uniform detector response. The contribution to jet
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energy from pileup is estimated
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on an event-by-event basis using the
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jet area method described in Ref.~\cite{cacciari-2008-659}, and is
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subtracted from the overall jet \pt. Jets that are
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consistent with anomalous noise in the calorimeter detectors are rejected.
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Jets are required to be consistent with originating from the
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signal primary vertex, to suppress jets from pileup events.
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Lepton ($\Pe, \mu$) candidates are required to be consistent with
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originating from a primary vertex.
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To reduce contamination due to leptons from heavy-flavor decay
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or misidentified hadrons in jets, leptons are required to be
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isolated and to have a transverse impact parameter with respect to the
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primary vertex satisfying $d_0 < 0.2$~mm.
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Electron and muon candidates are considered
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isolated if the ratio of the scalar sum of the transverse momenta of charged
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hadrons, photons, and neutral hadrons in a cone of
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$\Delta R = \sqrt{\Delta\eta^2+\Delta\phi^2}=0.3$
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around the candidate, relative to the lepton
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$\pt$ value, is less than 0.15.
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Standard electron and muon quality criteria are imposed.
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In the single lepton channel, in order to reduce the background from \ttbar events
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in which both W bosons decay leptonically (\ttll), events are
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rejected if they contain indications of an additional
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lepton: an isolated track with transverse
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momentum greater than 10 GeV (5 GeV for tracks that are loosely
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identified as electrons or muons) or a jet with $\pt> 20$ GeV
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consistent with the hadronic decay of a $\tau$ lepton~\cite{PFT-10-XXX}.
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To reduce the loss in signal acceptance, events with isolated
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tracks not loosely identified as electrons or muons
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are rejected only if the track has opposite charge with respect to the selected lepton.
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In the dilepton channel, only events with exactly two identified
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leptons are used, where the two leptons have opposite charge.
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Jets must satisfy $|\eta| < 2.4$ and $\pt > 30\GeV$ and
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be separated by $\Delta R > 0.4$ from candidate leptons.
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Jets originating from $\cPqb$ quarks (b-jets) are identified
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using the Combined Secondary Vertex loose or medium (CSVL and CSVM)
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working points~\cite{ref:btag}.
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The \MET, defined as the modulus of
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the vector sum of the transverse momenta of all PF objects, is
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required to be \MET\ $>$ 50 GeV.
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The search for \ttbar + 2 Higgs($\rightarrow b\bar{b}$) production
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proceeds by identifying events consistent with the production of a
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top quark pair with additional b jets.
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A typical event from the dominant \ttbar background has two b-jets
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in the final state, while signal events will have up to four
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additional b-jets. The requirement of more than 2 b-tags greatly
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suppresses \ttbar\ events. In order to maintain high signal
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efficiency, both events with 3 medium b-tags (with an additional loose
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b-tag not satisfying the medium requirement)
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and 4 or more medium b-tags are considered.
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The analysis in the single lepton channel focuses on events
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with large transverse mass of the lepton-\MET\ system, defined as
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$\mt = \sqrt{2 \pt^{\ell} \MET (1 - \cos(\phi))}$,
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where $\phi$ is the angle between the transverse momentum of the
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lepton and \MET. The requirement on \mt\ ($\mt>120$ or $>150$ GeV)
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provides large suppression of the semileptonic \ttbar\ background.
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The analysis in the dileptonic channel uses pairings of b-jets and a
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requirement is applied on the invariant mass of the $\bbbar$
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system $100~\le~\mbb~\le~150$. Only pairs with kinematics consistent with
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a $H\rightarrow \bbbar$ decay are considered, requiring
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$\Delta R(b,b)$~$\le$~2/3~$\pi$,
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[M(b,b)/$p_{T}$(b,b)]/$\Delta R(b,b)$~$\le$~0.65 and
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$|y(b)-y(b)|$~$\le$~1.2. In case of multiple \bbbar\ pairs,
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the pair with mass closest to m($H$)$\sim 125$~GeV is used. The signal
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region definitions are summarized in Table~\ref{tab:SummarySelection}.
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\begin{table}
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\caption{Summary of the signal region definitions.}
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\begin{center}
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\begin{tabular}{l|c|c|c|c|c}
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\hline
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Channel & \met & Lepton veto & N b-tag jets &\njets & Signal
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requirement \\
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\hline
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1 lepton & $\ge$~50 & track or $\tau_{h}$ & $=$~3b & $\ge$~5 & $\mt>150$~GeV \\
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& & & $\ge$~4b & $\ge$~4 & $\mt>120$~GeV \\
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\hline
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2 OS leptons & $\ge$~50 & extra e/$\mu$ & $=$~3b & $\ge$~5 & $100~\le~\mbb~\le~150$ \\
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& & & $\ge$~4b & $\ge$~4 & $100~\le~\mbb~\le~150$ \\
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\hline
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\end{tabular}
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\label{tab:SummarySelection}
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\end{center}
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\end{table}
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