Annotation of ttbar/p20_taujets_note/Preselection.tex, revision 1.2
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
1.2 ! uid12904 6: towards the final cross section measurement:
1.1 uid12904 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
1.2 ! uid12904 20: combined with the integrated luminosity measurement to calculate the cross section.
! 21: The systematic errors are estimated by changing
! 22: the values up-down by 1 sigma independently for each component
! 23: at a time and then propagating them through the entire procedure.
1.1 uid12904 24: \end{itemize}
25:
26: \section{\label{sub:Preselection}Preselection}
27:
28: The preselection is the first step of the analysis. The cuts presented here were chosen in order to provide the best
29: background reduction and enhance the $t\bar{t}$ content at this point. The cuts are the similar to those used in the
1.2 ! uid12904 30: p17 analysis \cite{p17_note} except that this time we optimized the value of $\not\!\! E_{T}$
1.1 uid12904 31: significance along with the sets of variables we used as inputs to NN training (Section \ref{sub:NN}).
32: 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}.
33:
34: %\begin{itemize}
35: %\item One $\tau$ lepton.
36: %\item $\not\!\! E_{T}$ arising from both the W vertex and $\tau$
37: %decay.
38: %\item At least 4 jets including two $b$-jets.
39: %\end{itemize}
40:
41: \begin{itemize}
1.2 ! uid12904 42: \item Duplicate event removal and event quality
! 43: \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
1.1 uid12904 44: \item at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV
45: \item 15 GeV $\leq$ $\not\!\! E_{T}$ $\leq$ 500 GeV
1.2 ! uid12904 46: \item $\not\!\! E_{T}$ significance $\geq$ 4.0.Missing transverse energy significance is a
! 47: measure of the likelihood of $\not\!\! E_{T}$
! 48: arising from physical sources. It is computed from calculated resolutions of physical objects (jets, electrons,
! 49: muons and unclustered energy) \cite{p17_note,METsig}.
! 50: \item Vertex selection: at least 3 tracks and $|z_{max}|$ = 60 cm.
! 51:
1.1 uid12904 52: \item No isolated electron or muon. This is done in order to ensure orthogonality with other \dzero \hspace{1pt}
53: measurements (\cite{l+jets} and \cite{dilepton}) - events that pass the lepton preselection cuts from these measurements
54: were vetoed. Also events that pass the all-jets analysis preselection cuts (described in the alljet analysis note \cite{alljet})
55: are rejected here.
56: \end{itemize}
57:
58:
59:
60: %\begin{figure}
61: %\label{cap:metl}
62: %\includegraphics[scale=0.6]{plots/metl}% Here is how to import EPS art
63: %\caption{$\not\!\! E_{T}$ significance for QCD-dominated data (black), $W+jets$ (blue) and $t\bar{t}\rightarrow\tau+jets$ (red).}
64: %\label{cap:met_significance}
65: %\end{figure}
66:
67: Among all preselection cuts one of them requires a more detailed description at this point since it represents
68: an improvement upon the old p17 analysis: $\not\!\! E_{T}$ significance.
1.2 ! uid12904 69: . Initially no $\not\!\! E_{T}$ significance
1.1 uid12904 70: was applied neither on MC nor on data. In this analysis we decided
71: to optimize the $\not\!\! E_{T}$ significance cut along with the NN optimization itself.
72: After finishing the $\not\!\! E_{T}$ significance optimization
73: part we went back and applied the optimized cut along with the non-optimized NNelec cut only to MC.
74: The entire optimization procedure is described in Section \ref{sub:NN-optimization}.
75:
76:
77: In data, initially the sample contained approximately 650 million events and the number of preselected events
78: (once again, without $\not\!\! E_{T}$ significance applied) is approximately 2.8 million events.
79:
80:
81: Another relevant aspect of the preselection is the usage of Particle Selector (only applied to MC samples).
1.2 ! uid12904 82: In this step we select a specific $\ttbar$ final state, namely, we split $W$ decay
1.1 uid12904 83: into $W \rightarrow e/\mu /\tau $ and
1.2 ! uid12904 84: tracked separate efficiencies for each of these processes. In this step we selected hadronic decays of tau.
! 85: Events where the tau decays into an electron or a muon were put into $e + jets$ and $\mu + jets$ samples.
! 86: As in p17, we decided to not split the dilepton sample in different lepton flavors.
1.1 uid12904 87:
88: As previously described, $t\bar{t}$ were generated by ALPGEN. In ALPGEN, different process with different
1.2 ! uid12904 89: numbers of partons have different cross sections and number of events. This fact must be taken into account when calculating the
! 90: efficiencies, namely, efficiencies must be properly scaled to the luminosity of the sample (4951.85 pb$^{-1}$). Tables
! 91: 7 and 8 show the ALPGEN weights for $t\bar{t} \rightarrow$ lepton + jets
1.1 uid12904 92: %VI and VII show the number beforementioned for $t\bar{t} \rightarrow$ lepton + jets
93: and $t\bar{t} \rightarrow$ dilepton respectively.
94:
95: \begin{table}[h]
96: \begin{center}
97: \begin{tabular}{|c|r|r|r|} \hline
1.2 ! uid12904 98: Process & \# of events & cross section (pb) & alpgen weight \\ \hline
1.1 uid12904 99:
100: \hline
101:
102:
1.2 ! uid12904 103: $t\bar{t}$ + 0 light parton & \multicolumn{1}{c|}{777068} & \multicolumn{1}{c|}{1.400} & \multicolumn{1}{c|}{0.00892} \\ \hline
1.1 uid12904 104:
105:
1.2 ! uid12904 106: $t\bar{t}$ + 1 light parton & \multicolumn{1}{c|}{457782} & \multicolumn{1}{c|}{0.577} & \multicolumn{1}{c|}{0.00624} \\ \hline
1.1 uid12904 107:
108:
1.2 ! uid12904 109: $t\bar{t}$ + $\geq$ 2 light partons & \multicolumn{1}{c|}{321166} & \multicolumn{1}{c|}{0.267} & \multicolumn{1}{c|}{0.00412} \\ \hline
1.1 uid12904 110: \end{tabular}
111: \caption{$t\bar{t} \rightarrow$ lepton + jets ALPGEN weights.}
112: \end{center}
113: \label{ttbar_alp}
114: \end{table}
115:
116:
117: \begin{table}[h]
118: \begin{center}
119: \begin{tabular}{|c|r|r|r|} \hline
1.2 ! uid12904 120: Process & \# of events & cross section (pb) & alpgen weight \\ \hline
1.1 uid12904 121:
122: \hline
123:
124:
125: 0 light parton & \multicolumn{1}{c|}{749642} & \multicolumn{1}{c|}{0.352} & \multicolumn{1}{c|}{0.00233} \\ \hline
126:
127:
128: 1 light parton & \multicolumn{1}{c|}{452177} & \multicolumn{1}{c|}{0.142} & \multicolumn{1}{c|}{0.00156} \\ \hline
129:
130:
131: $\geq$ 2 light partons & \multicolumn{1}{c|}{281453} & \multicolumn{1}{c|}{0.068} & \multicolumn{1}{c|}{0.00119} \\ \hline
132: \end{tabular}
133: \caption{$t\bar{t} \rightarrow$ dilepton ALPGEN weights.}
134: \end{center}
135: \label{dilep_alp}
136: \end{table}
137:
138: Tables \ref{taujets_cutflow}, \ref{ejets_cutflow}, \ref{mujets_cutflow} and
139: \ref{dilep_cutflow} show cut flows for all preselection cuts applied to different $\ttbar$ decays
140: (only statistical uncertainties are shown).
141:
142: %
143:
144: \begin{table}[h]
145: %\begin{center}
146: \begin{tabular}{ccccc}
147: \hline
148: Selection & Events & Relative & Cumulative \\ \hline Initial & 11164 & & \\
149: Particle selector & 2412 & $ 21.60 \pm 0.03 ~\% $ & $ 21.60 \pm 0.03~\% $ \\
150: Duplicate events removal & 2411 & $ 99.98 \pm 0.01 ~\% $ & $ 21.60 \pm 0.03~\% $ \\
151: Event quality & 2315 & $ 96.00 \pm 0.04 ~\% $ & $ 20.74 \pm 0.03~\% $ \\
152: Jet selection & 1307 & $ 59.45 \pm 0.09 ~\% $ & $ 11.70 \pm 0.03~\% $ \\
153: Vertex selection & 1296 & $ 99.18 \pm 0.02 ~\% $ & $ 11.61 \pm 0.03~\% $ \\
154: Electron veto & 1282 & $ 98.93 \pm 0.01 ~\% $ & $ 11.49 \pm 0.03~\% $ \\
155: Muon veto & 1282 & $ 99.93 \pm 0.01 ~\% $ & $ 11.48 \pm 0.03~\% $ \\
156: MET selection & 1218 & $ 95.05 \pm 0.05 ~\% $ & $ 10.91 \pm 0.02~\% $ \\
157: MET significance & 772 & $ 63.39 \pm 0.12 ~\% $ & $ 6.92 \pm 0.02~\% $ \\
1.2 ! uid12904 158: tau selection & 394 & $ 53.51 \pm 0.15 ~\% $ & $ 3.70 \pm 0.02~\% $ \\ \hline
1.1 uid12904 159:
160: \end{tabular}
161: \caption{Preselection $t\overline{t}\rightarrow\tau+jets$ cut flow}
162: %\end{center}
163: \label{taujets_cutflow}
164: \end{table}
165:
166: %\newpage
167:
168: \begin{table}[t]
169: %\begin{center}
170: \begin{tabular}{ccccc}
171: \hline
172: Selection & Events & Relative & Cumulative \\ \hline Initial & 11164 & & \\
173: Particle selector & 4385 & $ 39.28 \pm 0.04 ~\% $ & $ 39.28 \pm 0.04~\% $ \\
174: Duplicate event removal & 4383 & $ 99.96 \pm 0.01 ~\% $ & $ 39.26 \pm 0.04~\% $ \\
175: Event quality & 4207 & $ 95.97 \pm 0.03 ~\% $ & $ 37.68 \pm 0.04~\% $ \\
176: Jet selection & 1923 & $ 45.71 \pm 0.07 ~\% $ & $ 17.22 \pm 0.03~\% $ \\
177: Vertex selection & 1907 & $ 99.20 \pm 0.02 ~\% $ & $ 17.08 \pm 0.03~\% $ \\
178: Electron veto & 1048 & $ 54.94 \pm 0.10 ~\% $ & $ 9.39 \pm 0.02~\% $ \\
179: Muon veto & 1047 & $ 99.95 \pm 0.01 ~\% $ & $ 9.38 \pm 0.02~\% $ \\
180: MET selection & 1002 & $ 95.64 \pm 0.05~\% $ & $ 8.97 \pm 0.02~\% $ \\
181: MET significance & 669 & $ 66.74 \pm 0.13 ~\% $ & $ 5.99 \pm 0.02~\% $ \\
1.2 ! uid12904 182: tau selection & 395 & $ 59.12 \pm 0.16 ~\% $ & $ 3.54 \pm 0.02~\% $ \\ \hline
1.1 uid12904 183:
184: \end{tabular}
185: \caption{Preselection $t\overline{t}\rightarrow e+jets$ cut flow}
186: %\end{center}
187: \label{ejets_cutflow}
188: \end{table}
189:
190: %\clearpage
191:
192: \begin{table}[t]
193: %\begin{center}
194: \begin{tabular}{ccccc}
195: \hline
196: Selection & Events & Relative & Cumulative \\ \hline Initial & 11164 & & \\
197: Particle selector & 4367 & $ 39.12 \pm 0.04 ~\% $ & $ 39.12 \pm 0.04~\% $ \\
198: Duplicate event removal & 4366 & $ 99.96 \pm 0.04 ~\% $ & $ 39.10 \pm 0.04~\% $ \\
199: Event quality & 4189 & $ 95.95 \pm 0.03 ~\% $ & $ 37.52 \pm 0.04~\% $ \\
200: Jet selection & 1990 & $ 47.52 \pm 0.07 ~\% $ & $ 17.83 \pm 0.03~\% $ \\
201: Vertex selection & 1975 & $ 99.23 \pm 0.02 ~\% $ & $ 17.69 \pm 0.03~\% $ \\
202: Electron veto & 1967 & $ 99.59 \pm 0.01 ~\% $ & $ 17.62 \pm 0.03~\% $ \\
203: Muon veto & 1170 & $ 59.48 \pm 0.09 ~\% $ & $ 10.48 \pm 0.02~\% $ \\
204: MET selection & 1127 & $ 96.31 \pm 0.04~\% $ & $ 10.09 \pm 0.02~\% $ \\
205: MET significance & 812 & $ 72.06 \pm 0.11 ~\% $ & $ 7.27 \pm 0.02~\% $ \\
1.2 ! uid12904 206: tau selection & 186 & $ 22.95 \pm 0.13 ~\% $ & $ 1.67 \pm 0.01~\% $ \\ \hline
1.1 uid12904 207:
208: \end{tabular}
209: \caption{Preselection $t\overline{t}\rightarrow \mu +jets$ cut flow}
210: %\end{center}
211: \label{mujets_cutflow}
212: \end{table}
213:
214:
215: \begin{table}[b]
216: %\begin{center}
217: \begin{tabular}{ccccc}
218: \hline
219: Selection & Events & Relative & Cumulative \\ \hline Initial & 2799 & & \\
220: Particle selector & 2799 & $ 100.00 \pm 0.00 ~\% $ & $ 100.00 \pm 0.00~\% $ \\
221: Duplicate event removal & 2799 & $ 100.00 \pm 0.00 ~\% $ & $ 100.00 \pm 0.00~\% $ \\
222: Event quality & 2685 & $ 95.92 \pm 0.02 ~\% $ & $ 95.92 \pm 0.02~\% $ \\
223: Jet selection & 145 & $ 5.41 \pm 0.02 ~\% $ & $ 5.19 \pm 0.02~\% $ \\
224: Vertex selection & 144 & $ 99.32 \pm 0.03 ~\% $ & $ 5.16 \pm 0.02~\% $ \\
225: Electron veto & 110 & $ 76.14 \pm 0.13 ~\% $ & $ 3.93 \pm 0.01~\% $ \\
226: Muon veto & 83 & $ 75.08 \pm 0.16 ~\% $ & $ 2.95 \pm 0.01~\% $ \\
227: MET selection & 80 & $ 96.45 \pm 0.08~\% $ & $ 2.84 \pm 0.01~\% $ \\
228: MET significance & 60 & $ 75.32 \pm 0.19 ~\% $ & $ 2.14 \pm 0.01~\% $ \\
1.2 ! uid12904 229: tau selection & 38 & $ 63.21 \pm 0.24 ~\% $ & $ 1.35 \pm 0.01~\% $ \\ \hline
1.1 uid12904 230:
231: \end{tabular}
232: \caption{Preselection $t\overline{t}\rightarrow l+l$ cut flow}
233: %\end{center}
234: \label{dilep_cutflow}
235: \end{table}
236:
237: \clearpage
238:
239:
240:
241: %\clearpage
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