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\section{Search in the Same-sign Dilepton Final State}
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\label{sec:ss}
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This section presents a search in the same-sign (SS) dilepton final state, based on 10.5 fb$^{-1}$.
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A wide variety of new physics processes may produce events with SS leptons, which provide a very clean
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final state due to low SM background expectations. In particular, this final state is sensitive to
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direct pair production of bottom squarks with $\tilde{b}\to t \chi^{\pm}\to t W \lsp$ depicted in Fig.~\ref{fig:diagrams}(d),
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as well as to gluino-mediated production of top and bottom squarks.
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1.1 |
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We select events with two leptons (e or $\mu$) with \pt\ $>$ 20 GeV and dilepton invariant mass $m_{\ell\ell}>8$ GeV.
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We reject events with a third lepton with \pt\ $>$ 10 GeV that forms an opposite-sign
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same-flavor pair with $76 < m_{\ell\ell} < 106$ GeV with either selected lepton, to suppress
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the background from WZ and ZZ. We require the presence of at least two jets with \pt\ $>$ 40 GeV.
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This analysis is an extension of a previous search in the same-sign dilepton final state~\cite{ref:ss_inclusive}.
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In that analysis, the background is dominated by \ttljets\ where one lepton is from the W decay and the other
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lepton is produced in the decay of one of the b-jets. In this analysis we require the presence of at least two
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benhoob |
1.2 |
b-tagged jets (using CSVM). The requirement that both b-jets are identified and well-separated from the selected leptons
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1.1 |
reduces the \ttljets\ background by an order of magnitude.
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benhoob |
1.2 |
There are three sources of SM background passing the above preselection.
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The first background source is referred to as ``fake leptons'' and includes leptons from heavy-flavor decay,
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misidentified hadrons, muons from meson decay in flight, or electrons from unidentified photon conversions.
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This background is estimated from a sample of events with at least one lepton that passes a loose selection
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but fails the full analysis identification and isolation requirements. This sample is weighted by the probability
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for a fake lepton satisfying the loose selection to also pass the analysis selection, which is determined based
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on studies of fake
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leptons in jet events. The second background, estimated from MC, consists of rare SM processes and is dominated
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by $t\bar{t}$W and $t\bar{t}$Z. The systematic uncertainty on both the fake lepton and rare backgrounds is 50\%.
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A third, small background contributions is from ``charge flips'' and consists of events with opposite-sign leptons
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where one of the leptons is an electron whose charge is misreconstructed. This background is based on MC predictions,
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which are validated using a sample of Z$\to e^+e^-$ events.
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Signal regions are defined by placing additional requirements on the jet multiplicity, b-tagged jet multiplicity,
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\met, and $H_T$, defined as the scalar sum of the transverse momenta of selected jets. The observed data yields
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in these signal regions are compared to the SM background expectations in
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Table~\ref{tab:ss}. Good agreement is observed between the data and the expected background in all signal regions.
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In Fig.~\ref{fig:ss_interpretation}(a),tThe results are interpreted using the model of bottom squark pair
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production with $\tilde{b}\to t \chi^{\pm}$ depicted in Fig.~\ref{fig:diagrams}(d).
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The most sensitive signal region in most of the model parameter space is SR3 (see Table~\ref{tab:ss}).
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These results probe bottom squarks with masses up to 450 GeV.
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The constraint on the bottom squark mass from naturalness is similar to that on the top squark, requiring
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a mass less than 500-700~GeV. Several additional interpretations for models with gluino-mediated top and
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bottom squark production are presented in Ref.~\cite{ref:ss}.
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benhoob |
1.1 |
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%\begin{table}
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%\centering
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%\caption{Please write your table caption here}
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%\label{tab-1} % Give a unique label
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%% For LaTeX tables you can use
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%\begin{tabular}{lll}
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%\hline
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%first & second & third \\\hline
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%number & number & number \\
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%number & number & number \\\hline
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%\end{tabular}
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%% Or use
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%\vspace*{5cm} % with the correct table height
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%\end{table}
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\begin{table*}[t]
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\centering
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\caption{\label{tab:ss} Summary of the results of the search in the same-sign dilepton final state.
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Several signal regions (SR) are indicated, including the kinematic requirements, the prediction of the three background (BG) contributions,
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the total background, and the observed yield in data. The jet multiplicity requirement in the first row includes both b-tagged and untagged jets. The uncertainty includes the statistical and systematic components.}
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\tabcolsep 2.7pt
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\begin{scriptsize}
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\begin{tabular}{l|c|c|c|c|c|c|c|c|c}
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\hline
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\hline
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& SR0 & SR1 & SR2 & SR3 & SR4 & SR5 & SR6 & SR7 & SR8 \\
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\hline
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No. of jets & $\geq 2$ & $\geq 2$ & $\geq 2$ & $\geq 4$ & $\geq 4$ & $\geq 4$ & $\geq 4$ & $\geq 3$ & $\geq 4$ \\
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No. of btags & $\geq 2$ & $\geq 2$ & $\geq 2$ & $\geq 2$ & $\geq 2$ & $\geq 2$ & $\geq 2$ & $\geq 3$ & $\geq 2$ \\
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Lepton charges & $++/--$ & $++/--$ & $++$ & $++/--$ & $++/--$ & $++/--$ & $++/--$ & $++/--$ & $++/--$ \\
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\met & $> 0$ GeV & $> 30$ GeV & $> 30$ GeV & $> 120$ GeV & $> 50$ GeV & $> 50$ GeV & $> 120$ GeV & $> 50$ GeV & $> 0$ GeV \\
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$H_T$ & $> 80$ GeV & $> 80$ GeV & $> 80$ GeV & $> 200$ GeV & $> 200$ GeV & $> 320$ GeV & $> 320$ GeV & $> 200$ GeV & $> 320$ GeV \\
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\hline
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Charge-flip BG & $3.35 \pm 0.67$ & $2.70 \pm 0.54$ & $1.35 \pm 0.27$ & $0.04 \pm 0.01$ & $0.21 \pm 0.05$ & $0.14 \pm 0.03$ & $0.04 \pm 0.01$ & $0.03 \pm 0.01$ & $0.21 \pm 0.05$\\
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Fake BG & $24.77 \pm 12.62$ & $19.18 \pm 9.83$ & $9.59 \pm 5.02$ & $0.99 \pm 0.69$ & $4.51 \pm 2.85$ & $2.88 \pm 1.69$ & $0.67 \pm 0.48$ & $0.71 \pm 0.47$ & $4.39 \pm 2.64$ \\
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Rare SM BG & $11.75 \pm 5.89$ & $10.46 \pm 5.25$ & $6.73 \pm 3.39$ & $1.18 \pm 0.67$ & $3.35 \pm 1.84$ & $2.66 \pm 1.47$ & $1.02 \pm 0.60$ & $0.44 \pm 0.39$ & $3.50 \pm 1.92$ \\
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\hline
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Total BG & $39.87 \pm 13.94$ & $32.34 \pm 11.16$ & $17.67 \pm 6.06$ & $2.22 \pm 0.96$ & $8.07 \pm 3.39$ & $5.67 \pm 2.24$ & $1.73 \pm 0.77$ & $1.18 \pm 0.61$ & $8.11 \pm 3.26$ \\
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Event yield & 43 & 38 & 14 & 1 & 10 & 7 & 1 & 1 & 9 \\
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\hline
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% $N_{{UL}}$ (13\% unc.) & 27.2 &26.0 &9.9 &3.6 &10.8 &8.6 &3.6 &3.7 &9.6 \\
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% $N_{{UL}}$ (20\% unc.) & 28.2 &27.2 &10.2 &3.6 &11.2 &8.9 &3.7 &3.8 &9.9 \\
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% $N_{{UL}}$ (30\% unc.) & 30.4 &29.6 &10.7 &3.8 &12.0 &9.6 &3.9 &4.0 &10.5 \\
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\hline
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\end{tabular}
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\end{scriptsize}
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\end{table*}
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benhoob |
1.3 |
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\begin{figure*}
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\centering
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%\begin{center}
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\begin{tabular}{cc}
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\subfloat[] {\includegraphics[width=0.5\textwidth]{HCPPlots/SS_B1.pdf}} &
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\subfloat[] {\includegraphics[width=0.4\textwidth]{HCPPlots/T2bb_interpretation.pdf}} \\
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\end{tabular}
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\caption{
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Interpretation of the results of the search in (a) the same-sign dilepton final state for
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bottom squark pair production with $\tilde{b}\to t\chip$ depicted in Fig.~\ref{fig:diagrams}(d), and (b)
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the all-hadronic final state for bottom squark pair production with $\tilde{b}\to b\lsp$ depicted in Fig.~\ref{fig:diagrams}(c).
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\label{fig:ss_interpretation}
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}
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%\end{center}
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\end{figure*}
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