Annotation of ttbar/p20_taujets_note/Preselection.tex, revision 1.1
1.1 ! uid12904 1: \section{Analysis outline}
! 2: Up to this point we have presented the data sample used in this analysis (Section \ref{sub:datasample})
! 3: the Monte Carlo samples and corrections applied to them (Sections \ref{sub:mcsample} and \ref{sub:mcsample_xseccorr}),
! 4: the trigger used and its simulation (Section \ref{sec:trig_param}) and the object ID
! 5: method (Section \ref{sec:objects}). Now we describe the next steps of the analysis
! 6: towards the final crosse section measurement:
! 7:
! 8: \begin{itemize}
! 9: \item Preselection (section \ref{sub:Preselection}): at least 4 jets, at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV/$c$,
! 10: 15 GeV $\leq$ $\not\!\! E_{T}$ $\leq$ 500 GeV and $\not\!\! E_{T}$ significance $>$4.0.
! 11: \item $\tau$- and b-ID cuts (section \ref{sub:Results-of-the}): at least one good $\tau$ lepton
! 12: candidate and at least one tight NN b-tag are required.
! 13: \item Topological NN (section \ref{sub:NN-variables}): a
! 14: feed-forward NN's is trained in order to provide signal-background separation. The NN
! 15: was optimized by testing different sets of topological variables as its inputs and by applying
! 16: different $\not\!\! E_{T}$ significance cuts.
! 17: \item Topological Variables (section \ref{sub:Topo}): section showing final analysis plots of topological
! 18: variables of interest.
! 19: \item Cross Section (section \ref{sub:xsect}) The signal fraction determination is
! 20: combined with integrated luminosity measurement to calculate the cross section.
! 21: Systematic uncertainties are determined by fluctuating the significant components
! 22: up and down by one standard deviation one at a time, propagating it through the entire procedure.
! 23: \end{itemize}
! 24:
! 25: \section{\label{sub:Preselection}Preselection}
! 26:
! 27: The preselection is the first step of the analysis. The cuts presented here were chosen in order to provide the best
! 28: background reduction and enhance the $t\bar{t}$ content at this point. The cuts are the similar to those used in the
! 29: p17 analysis \cite{p17_note} except that for this time we opted to optimize the value of $\not\!\! E_{T}$
! 30: significance along with the sets of variables we used as inputs to NN training (Section \ref{sub:NN}).
! 31: Cuts shown below were applied to samples shown in Table \ref{used_mc} as well as to data as shown in Section \ref{sub:datasample}.
! 32:
! 33: %\begin{itemize}
! 34: %\item One $\tau$ lepton.
! 35: %\item $\not\!\! E_{T}$ arising from both the W vertex and $\tau$
! 36: %decay.
! 37: %\item At least 4 jets including two $b$-jets.
! 38: %\end{itemize}
! 39:
! 40: \begin{itemize}
! 41: \item At least 4 jets with $p_{T}>15$ GeV and $\eta <$2.5, with leading (in $p_{T}$) jet $p_{T}>35$ GeV and second and third jets have $p_{T}>25$ GeV
! 42: \item at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV
! 43: \item 15 GeV $\leq$ $\not\!\! E_{T}$ $\leq$ 500 GeV
! 44: \item $\not\!\! E_{T}$ significance $\geq$ 4.0
! 45: \item No isolated electron or muon. This is done in order to ensure orthogonality with other \dzero \hspace{1pt}
! 46: measurements (\cite{l+jets} and \cite{dilepton}) - events that pass the lepton preselection cuts from these measurements
! 47: were vetoed. Also events that pass the all-jets analysis preselection cuts (described in the alljet analysis note \cite{alljet})
! 48: are rejected here.
! 49: \end{itemize}
! 50:
! 51:
! 52:
! 53: %\begin{figure}
! 54: %\label{cap:metl}
! 55: %\includegraphics[scale=0.6]{plots/metl}% Here is how to import EPS art
! 56: %\caption{$\not\!\! E_{T}$ significance for QCD-dominated data (black), $W+jets$ (blue) and $t\bar{t}\rightarrow\tau+jets$ (red).}
! 57: %\label{cap:met_significance}
! 58: %\end{figure}
! 59:
! 60: Among all preselection cuts one of them requires a more detailed description at this point since it represents
! 61: an improvement upon the old p17 analysis: $\not\!\! E_{T}$ significance.
! 62: Missing transverse energy significance is a measure of the likelihood of $\not\!\! E_{T}$
! 63: arising from physical sources. It is computed from calculated resolutions of physical objects (jets, electrons,
! 64: muons and unclustered energy) \cite{p17_note,METsig}. Initially no $\not\!\! E_{T}$ significance
! 65: was applied neither on MC nor on data. In this analysis we decided
! 66: to optimize the $\not\!\! E_{T}$ significance cut along with the NN optimization itself.
! 67: After finishing the $\not\!\! E_{T}$ significance optimization
! 68: part we went back and applied the optimized cut along with the non-optimized NNelec cut only to MC.
! 69: The entire optimization procedure is described in Section \ref{sub:NN-optimization}.
! 70:
! 71:
! 72: In data, initially the sample contained approximately 650 million events and the number of preselected events
! 73: (once again, without $\not\!\! E_{T}$ significance applied) is approximately 2.8 million events.
! 74:
! 75:
! 76: Another relevant aspect of the preselection is the usage of Particle Selector (only applied to MC samples).
! 77: In this step we aimed to select a particular $\ttbar$ final state, namely, we split $W$ decay
! 78: into $W \rightarrow e/\mu /\tau $ and
! 79: tracked separate efficiencies for each of these processes. In this step we selected hadronic decays of tau,
! 80: and at the same events where tau decays into electrons and muons were put into $e + jets$ and $\mu + jets$ samples.
! 81: As in p17, we decided to do not split the dilepton sample in different lepton flavors.
! 82:
! 83: Before proceeding to the next step, it is important to describe the result of the preselection
! 84: in terms of its efficiencies since all the rest of analysis strongly depends on the cuts applied at this level.
! 85: As previously described, $t\bar{t}$ were generated by ALPGEN. In ALPGEN, different process with different
! 86: numbers of partons have different cross-sections and number of events. This fact must be taken into account when calculating the
! 87: efficiencies, namely, efficiencies must be properly scaled to the luminosity (4951.85 pb$^{-1}$) of the sample. Tables
! 88: \ref{ttbar_alp} and III show the number beforementioned for $t\bar{t} \rightarrow$ lepton + jets
! 89: %VI and VII show the number beforementioned for $t\bar{t} \rightarrow$ lepton + jets
! 90: and $t\bar{t} \rightarrow$ dilepton respectively.
! 91:
! 92: \begin{table}[h]
! 93: \begin{center}
! 94: \begin{tabular}{|c|r|r|r|} \hline
! 95: Process & \# of events & cross-section (pb) & alpgen weight \\ \hline
! 96:
! 97: \hline
! 98:
! 99:
! 100: 0 light parton & \multicolumn{1}{c|}{777068} & \multicolumn{1}{c|}{1.4} & \multicolumn{1}{c|}{0.00892} \\ \hline
! 101:
! 102:
! 103: 1 light parton & \multicolumn{1}{c|}{457782} & \multicolumn{1}{c|}{0.577} & \multicolumn{1}{c|}{0.00624} \\ \hline
! 104:
! 105:
! 106: $\geq$ 2 light partons & \multicolumn{1}{c|}{321166} & \multicolumn{1}{c|}{0.267} & \multicolumn{1}{c|}{0.00412} \\ \hline
! 107: \end{tabular}
! 108: \caption{$t\bar{t} \rightarrow$ lepton + jets ALPGEN weights.}
! 109: \end{center}
! 110: \label{ttbar_alp}
! 111: \end{table}
! 112:
! 113:
! 114: \begin{table}[h]
! 115: \begin{center}
! 116: \begin{tabular}{|c|r|r|r|} \hline
! 117: Process & \# of events & cross-section (pb) & alpgen weight \\ \hline
! 118:
! 119: \hline
! 120:
! 121:
! 122: 0 light parton & \multicolumn{1}{c|}{749642} & \multicolumn{1}{c|}{0.352} & \multicolumn{1}{c|}{0.00233} \\ \hline
! 123:
! 124:
! 125: 1 light parton & \multicolumn{1}{c|}{452177} & \multicolumn{1}{c|}{0.142} & \multicolumn{1}{c|}{0.00156} \\ \hline
! 126:
! 127:
! 128: $\geq$ 2 light partons & \multicolumn{1}{c|}{281453} & \multicolumn{1}{c|}{0.068} & \multicolumn{1}{c|}{0.00119} \\ \hline
! 129: \end{tabular}
! 130: \caption{$t\bar{t} \rightarrow$ dilepton ALPGEN weights.}
! 131: \end{center}
! 132: \label{dilep_alp}
! 133: \end{table}
! 134:
! 135: Tables \ref{taujets_cutflow}, \ref{ejets_cutflow}, \ref{mujets_cutflow} and
! 136: \ref{dilep_cutflow} show cut flows for all preselection cuts applied to different $\ttbar$ decays
! 137: (only statistical uncertainties are shown).
! 138:
! 139: %
! 140:
! 141: \begin{table}[h]
! 142: %\begin{center}
! 143: \begin{tabular}{ccccc}
! 144: \hline
! 145: Selection & Events & Relative & Cumulative \\ \hline Initial & 11164 & & \\
! 146: Particle selector & 2412 & $ 21.60 \pm 0.03 ~\% $ & $ 21.60 \pm 0.03~\% $ \\
! 147: Duplicate events removal & 2411 & $ 99.98 \pm 0.01 ~\% $ & $ 21.60 \pm 0.03~\% $ \\
! 148: Event quality & 2315 & $ 96.00 \pm 0.04 ~\% $ & $ 20.74 \pm 0.03~\% $ \\
! 149: Jet selection & 1307 & $ 59.45 \pm 0.09 ~\% $ & $ 11.70 \pm 0.03~\% $ \\
! 150: Vertex selection & 1296 & $ 99.18 \pm 0.02 ~\% $ & $ 11.61 \pm 0.03~\% $ \\
! 151: Electron veto & 1282 & $ 98.93 \pm 0.01 ~\% $ & $ 11.49 \pm 0.03~\% $ \\
! 152: Muon veto & 1282 & $ 99.93 \pm 0.01 ~\% $ & $ 11.48 \pm 0.03~\% $ \\
! 153: MET selection & 1218 & $ 95.05 \pm 0.05 ~\% $ & $ 10.91 \pm 0.02~\% $ \\
! 154: MET significance & 772 & $ 63.39 \pm 0.12 ~\% $ & $ 6.92 \pm 0.02~\% $ \\
! 155: NN tau cut & 394 & $ 53.51 \pm 0.15 ~\% $ & $ 3.70 \pm 0.02~\% $ \\ \hline
! 156:
! 157: \end{tabular}
! 158: \caption{Preselection $t\overline{t}\rightarrow\tau+jets$ cut flow}
! 159: %\end{center}
! 160: \label{taujets_cutflow}
! 161: \end{table}
! 162:
! 163: %\newpage
! 164:
! 165: \begin{table}[t]
! 166: %\begin{center}
! 167: \begin{tabular}{ccccc}
! 168: \hline
! 169: Selection & Events & Relative & Cumulative \\ \hline Initial & 11164 & & \\
! 170: Particle selector & 4385 & $ 39.28 \pm 0.04 ~\% $ & $ 39.28 \pm 0.04~\% $ \\
! 171: Duplicate event removal & 4383 & $ 99.96 \pm 0.01 ~\% $ & $ 39.26 \pm 0.04~\% $ \\
! 172: Event quality & 4207 & $ 95.97 \pm 0.03 ~\% $ & $ 37.68 \pm 0.04~\% $ \\
! 173: Jet selection & 1923 & $ 45.71 \pm 0.07 ~\% $ & $ 17.22 \pm 0.03~\% $ \\
! 174: Vertex selection & 1907 & $ 99.20 \pm 0.02 ~\% $ & $ 17.08 \pm 0.03~\% $ \\
! 175: Electron veto & 1048 & $ 54.94 \pm 0.10 ~\% $ & $ 9.39 \pm 0.02~\% $ \\
! 176: Muon veto & 1047 & $ 99.95 \pm 0.01 ~\% $ & $ 9.38 \pm 0.02~\% $ \\
! 177: MET selection & 1002 & $ 95.64 \pm 0.05~\% $ & $ 8.97 \pm 0.02~\% $ \\
! 178: MET significance & 669 & $ 66.74 \pm 0.13 ~\% $ & $ 5.99 \pm 0.02~\% $ \\
! 179: NN tau cut & 395 & $ 59.12 \pm 0.16 ~\% $ & $ 3.54 \pm 0.02~\% $ \\ \hline
! 180:
! 181: \end{tabular}
! 182: \caption{Preselection $t\overline{t}\rightarrow e+jets$ cut flow}
! 183: %\end{center}
! 184: \label{ejets_cutflow}
! 185: \end{table}
! 186:
! 187: %\clearpage
! 188:
! 189: \begin{table}[t]
! 190: %\begin{center}
! 191: \begin{tabular}{ccccc}
! 192: \hline
! 193: Selection & Events & Relative & Cumulative \\ \hline Initial & 11164 & & \\
! 194: Particle selector & 4367 & $ 39.12 \pm 0.04 ~\% $ & $ 39.12 \pm 0.04~\% $ \\
! 195: Duplicate event removal & 4366 & $ 99.96 \pm 0.04 ~\% $ & $ 39.10 \pm 0.04~\% $ \\
! 196: Event quality & 4189 & $ 95.95 \pm 0.03 ~\% $ & $ 37.52 \pm 0.04~\% $ \\
! 197: Jet selection & 1990 & $ 47.52 \pm 0.07 ~\% $ & $ 17.83 \pm 0.03~\% $ \\
! 198: Vertex selection & 1975 & $ 99.23 \pm 0.02 ~\% $ & $ 17.69 \pm 0.03~\% $ \\
! 199: Electron veto & 1967 & $ 99.59 \pm 0.01 ~\% $ & $ 17.62 \pm 0.03~\% $ \\
! 200: Muon veto & 1170 & $ 59.48 \pm 0.09 ~\% $ & $ 10.48 \pm 0.02~\% $ \\
! 201: MET selection & 1127 & $ 96.31 \pm 0.04~\% $ & $ 10.09 \pm 0.02~\% $ \\
! 202: MET significance & 812 & $ 72.06 \pm 0.11 ~\% $ & $ 7.27 \pm 0.02~\% $ \\
! 203: NN tau cut & 186 & $ 22.95 \pm 0.13 ~\% $ & $ 1.67 \pm 0.01~\% $ \\ \hline
! 204:
! 205: \end{tabular}
! 206: \caption{Preselection $t\overline{t}\rightarrow \mu +jets$ cut flow}
! 207: %\end{center}
! 208: \label{mujets_cutflow}
! 209: \end{table}
! 210:
! 211:
! 212: \begin{table}[b]
! 213: %\begin{center}
! 214: \begin{tabular}{ccccc}
! 215: \hline
! 216: Selection & Events & Relative & Cumulative \\ \hline Initial & 2799 & & \\
! 217: Particle selector & 2799 & $ 100.00 \pm 0.00 ~\% $ & $ 100.00 \pm 0.00~\% $ \\
! 218: Duplicate event removal & 2799 & $ 100.00 \pm 0.00 ~\% $ & $ 100.00 \pm 0.00~\% $ \\
! 219: Event quality & 2685 & $ 95.92 \pm 0.02 ~\% $ & $ 95.92 \pm 0.02~\% $ \\
! 220: Jet selection & 145 & $ 5.41 \pm 0.02 ~\% $ & $ 5.19 \pm 0.02~\% $ \\
! 221: Vertex selection & 144 & $ 99.32 \pm 0.03 ~\% $ & $ 5.16 \pm 0.02~\% $ \\
! 222: Electron veto & 110 & $ 76.14 \pm 0.13 ~\% $ & $ 3.93 \pm 0.01~\% $ \\
! 223: Muon veto & 83 & $ 75.08 \pm 0.16 ~\% $ & $ 2.95 \pm 0.01~\% $ \\
! 224: MET selection & 80 & $ 96.45 \pm 0.08~\% $ & $ 2.84 \pm 0.01~\% $ \\
! 225: MET significance & 60 & $ 75.32 \pm 0.19 ~\% $ & $ 2.14 \pm 0.01~\% $ \\
! 226: NN tau cut & 38 & $ 63.21 \pm 0.24 ~\% $ & $ 1.35 \pm 0.01~\% $ \\ \hline
! 227:
! 228: \end{tabular}
! 229: \caption{Preselection $t\overline{t}\rightarrow l+l$ cut flow}
! 230: %\end{center}
! 231: \label{dilep_cutflow}
! 232: \end{table}
! 233:
! 234: \clearpage
! 235:
! 236:
! 237:
! 238: %\clearpage
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