Annotation of ttbar/p20_taujets_note/Preselection.tex, revision 1.1.1.1
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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