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version 1.1, 2011/05/18 21:30:39
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version 1.2, 2011/06/01 01:20:54
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Line 3 Up to this point we have presented the d
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Line 3 Up to this point we have presented the d
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| the Monte Carlo samples and corrections applied to them (Sections \ref{sub:mcsample} and \ref{sub:mcsample_xseccorr}), |
the Monte Carlo samples and corrections applied to them (Sections \ref{sub:mcsample} and \ref{sub:mcsample_xseccorr}), |
| the trigger used and its simulation (Section \ref{sec:trig_param}) and the object ID |
the trigger used and its simulation (Section \ref{sec:trig_param}) and the object ID |
| method (Section \ref{sec:objects}). Now we describe the next steps of the analysis |
method (Section \ref{sec:objects}). Now we describe the next steps of the analysis |
| towards the final crosse section measurement: |
towards the final cross section measurement: |
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| \begin{itemize} |
\begin{itemize} |
| \item Preselection (section \ref{sub:Preselection}): at least 4 jets, at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV/$c$, |
\item Preselection (section \ref{sub:Preselection}): at least 4 jets, at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV/$c$, |
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Line 17 different $\not\!\! E_{T}$ significance
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Line 17 different $\not\!\! E_{T}$ significance
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| \item Topological Variables (section \ref{sub:Topo}): section showing final analysis plots of topological |
\item Topological Variables (section \ref{sub:Topo}): section showing final analysis plots of topological |
| variables of interest. |
variables of interest. |
| \item Cross Section (section \ref{sub:xsect}) The signal fraction determination is |
\item Cross Section (section \ref{sub:xsect}) The signal fraction determination is |
| combined with integrated luminosity measurement to calculate the cross section. |
combined with the integrated luminosity measurement to calculate the cross section. |
| Systematic uncertainties are determined by fluctuating the significant components |
The systematic errors are estimated by changing |
| up and down by one standard deviation one at a time, propagating it through the entire procedure. |
the values up-down by 1 sigma independently for each component |
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at a time and then propagating them through the entire procedure. |
| \end{itemize} |
\end{itemize} |
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| \section{\label{sub:Preselection}Preselection} |
\section{\label{sub:Preselection}Preselection} |
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| The preselection is the first step of the analysis. The cuts presented here were chosen in order to provide the best |
The preselection is the first step of the analysis. The cuts presented here were chosen in order to provide the best |
| background reduction and enhance the $t\bar{t}$ content at this point. The cuts are the similar to those used in the |
background reduction and enhance the $t\bar{t}$ content at this point. The cuts are the similar to those used in the |
| p17 analysis \cite{p17_note} except that for this time we opted to optimize the value of $\not\!\! E_{T}$ |
p17 analysis \cite{p17_note} except that this time we optimized the value of $\not\!\! E_{T}$ |
| significance along with the sets of variables we used as inputs to NN training (Section \ref{sub:NN}). |
significance along with the sets of variables we used as inputs to NN training (Section \ref{sub:NN}). |
| 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}. |
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}. |
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Line 38 Cuts shown below were applied to samples
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Line 39 Cuts shown below were applied to samples
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| %\end{itemize} |
%\end{itemize} |
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|
| \begin{itemize} |
\begin{itemize} |
| \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 |
\item Duplicate event removal and event quality |
| |
\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 |
| \item at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV |
\item at least one $\tau$ with NN$>$0.3 and $p_{T}>10$ GeV |
| \item 15 GeV $\leq$ $\not\!\! E_{T}$ $\leq$ 500 GeV |
\item 15 GeV $\leq$ $\not\!\! E_{T}$ $\leq$ 500 GeV |
| \item $\not\!\! E_{T}$ significance $\geq$ 4.0 |
\item $\not\!\! E_{T}$ significance $\geq$ 4.0.Missing transverse energy significance is a |
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measure of the likelihood of $\not\!\! E_{T}$ |
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arising from physical sources. It is computed from calculated resolutions of physical objects (jets, electrons, |
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muons and unclustered energy) \cite{p17_note,METsig}. |
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\item Vertex selection: at least 3 tracks and $|z_{max}|$ = 60 cm. |
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| \item No isolated electron or muon. This is done in order to ensure orthogonality with other \dzero \hspace{1pt} |
\item No isolated electron or muon. This is done in order to ensure orthogonality with other \dzero \hspace{1pt} |
| measurements (\cite{l+jets} and \cite{dilepton}) - events that pass the lepton preselection cuts from these measurements |
measurements (\cite{l+jets} and \cite{dilepton}) - events that pass the lepton preselection cuts from these measurements |
| were vetoed. Also events that pass the all-jets analysis preselection cuts (described in the alljet analysis note \cite{alljet}) |
were vetoed. Also events that pass the all-jets analysis preselection cuts (described in the alljet analysis note \cite{alljet}) |
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Line 59 are rejected here.
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Line 66 are rejected here.
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| Among all preselection cuts one of them requires a more detailed description at this point since it represents |
Among all preselection cuts one of them requires a more detailed description at this point since it represents |
| an improvement upon the old p17 analysis: $\not\!\! E_{T}$ significance. |
an improvement upon the old p17 analysis: $\not\!\! E_{T}$ significance. |
| Missing transverse energy significance is a measure of the likelihood of $\not\!\! E_{T}$ |
. Initially no $\not\!\! E_{T}$ significance |
| arising from physical sources. It is computed from calculated resolutions of physical objects (jets, electrons, |
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| muons and unclustered energy) \cite{p17_note,METsig}. Initially no $\not\!\! E_{T}$ significance |
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| was applied neither on MC nor on data. In this analysis we decided |
was applied neither on MC nor on data. In this analysis we decided |
| to optimize the $\not\!\! E_{T}$ significance cut along with the NN optimization itself. |
to optimize the $\not\!\! E_{T}$ significance cut along with the NN optimization itself. |
| After finishing the $\not\!\! E_{T}$ significance optimization |
After finishing the $\not\!\! E_{T}$ significance optimization |
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Line 74 In data, initially the sample contained
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Line 79 In data, initially the sample contained
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| Another relevant aspect of the preselection is the usage of Particle Selector (only applied to MC samples). |
Another relevant aspect of the preselection is the usage of Particle Selector (only applied to MC samples). |
| In this step we aimed to select a particular $\ttbar$ final state, namely, we split $W$ decay |
In this step we select a specific $\ttbar$ final state, namely, we split $W$ decay |
| into $W \rightarrow e/\mu /\tau $ and |
into $W \rightarrow e/\mu /\tau $ and |
| tracked separate efficiencies for each of these processes. In this step we selected hadronic decays of tau, |
tracked separate efficiencies for each of these processes. In this step we selected hadronic decays of tau. |
| and at the same events where tau decays into electrons and muons were put into $e + jets$ and $\mu + jets$ samples. |
Events where the tau decays into an electron or a muon were put into $e + jets$ and $\mu + jets$ samples. |
| As in p17, we decided to do not split the dilepton sample in different lepton flavors. |
As in p17, we decided to not split the dilepton sample in different lepton flavors. |
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| Before proceeding to the next step, it is important to describe the result of the preselection |
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| in terms of its efficiencies since all the rest of analysis strongly depends on the cuts applied at this level. |
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| As previously described, $t\bar{t}$ were generated by ALPGEN. In ALPGEN, different process with different |
As previously described, $t\bar{t}$ were generated by ALPGEN. In ALPGEN, different process with different |
| numbers of partons have different cross-sections and number of events. This fact must be taken into account when calculating the |
numbers of partons have different cross sections and number of events. This fact must be taken into account when calculating the |
| efficiencies, namely, efficiencies must be properly scaled to the luminosity (4951.85 pb$^{-1}$) of the sample. Tables |
efficiencies, namely, efficiencies must be properly scaled to the luminosity of the sample (4951.85 pb$^{-1}$). Tables |
| \ref{ttbar_alp} and III show the number beforementioned for $t\bar{t} \rightarrow$ lepton + jets |
7 and 8 show the ALPGEN weights for $t\bar{t} \rightarrow$ lepton + jets |
| %VI and VII show the number beforementioned for $t\bar{t} \rightarrow$ lepton + jets |
%VI and VII show the number beforementioned for $t\bar{t} \rightarrow$ lepton + jets |
| and $t\bar{t} \rightarrow$ dilepton respectively. |
and $t\bar{t} \rightarrow$ dilepton respectively. |
| |
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| \begin{table}[h] |
\begin{table}[h] |
| \begin{center} |
\begin{center} |
| \begin{tabular}{|c|r|r|r|} \hline |
\begin{tabular}{|c|r|r|r|} \hline |
| Process & \# of events & cross-section (pb) & alpgen weight \\ \hline |
Process & \# of events & cross section (pb) & alpgen weight \\ \hline |
| |
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| \hline |
\hline |
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| 0 light parton & \multicolumn{1}{c|}{777068} & \multicolumn{1}{c|}{1.4} & \multicolumn{1}{c|}{0.00892} \\ \hline |
$t\bar{t}$ + 0 light parton & \multicolumn{1}{c|}{777068} & \multicolumn{1}{c|}{1.400} & \multicolumn{1}{c|}{0.00892} \\ \hline |
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| 1 light parton & \multicolumn{1}{c|}{457782} & \multicolumn{1}{c|}{0.577} & \multicolumn{1}{c|}{0.00624} \\ \hline |
$t\bar{t}$ + 1 light parton & \multicolumn{1}{c|}{457782} & \multicolumn{1}{c|}{0.577} & \multicolumn{1}{c|}{0.00624} \\ \hline |
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| $\geq$ 2 light partons & \multicolumn{1}{c|}{321166} & \multicolumn{1}{c|}{0.267} & \multicolumn{1}{c|}{0.00412} \\ \hline |
$t\bar{t}$ + $\geq$ 2 light partons & \multicolumn{1}{c|}{321166} & \multicolumn{1}{c|}{0.267} & \multicolumn{1}{c|}{0.00412} \\ \hline |
| \end{tabular} |
\end{tabular} |
| \caption{$t\bar{t} \rightarrow$ lepton + jets ALPGEN weights.} |
\caption{$t\bar{t} \rightarrow$ lepton + jets ALPGEN weights.} |
| \end{center} |
\end{center} |
|
Line 114 $\geq$ 2 light partons & \multicolu
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Line 117 $\geq$ 2 light partons & \multicolu
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| \begin{table}[h] |
\begin{table}[h] |
| \begin{center} |
\begin{center} |
| \begin{tabular}{|c|r|r|r|} \hline |
\begin{tabular}{|c|r|r|r|} \hline |
| Process & \# of events & cross-section (pb) & alpgen weight \\ \hline |
Process & \# of events & cross section (pb) & alpgen weight \\ \hline |
| |
|
| \hline |
\hline |
| |
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Line 152 Electron veto & 1282 & $ 98.93 \pm 0.01
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Line 155 Electron veto & 1282 & $ 98.93 \pm 0.01
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| Muon veto & 1282 & $ 99.93 \pm 0.01 ~\% $ & $ 11.48 \pm 0.03~\% $ \\ |
Muon veto & 1282 & $ 99.93 \pm 0.01 ~\% $ & $ 11.48 \pm 0.03~\% $ \\ |
| MET selection & 1218 & $ 95.05 \pm 0.05 ~\% $ & $ 10.91 \pm 0.02~\% $ \\ |
MET selection & 1218 & $ 95.05 \pm 0.05 ~\% $ & $ 10.91 \pm 0.02~\% $ \\ |
| MET significance & 772 & $ 63.39 \pm 0.12 ~\% $ & $ 6.92 \pm 0.02~\% $ \\ |
MET significance & 772 & $ 63.39 \pm 0.12 ~\% $ & $ 6.92 \pm 0.02~\% $ \\ |
| NN tau cut & 394 & $ 53.51 \pm 0.15 ~\% $ & $ 3.70 \pm 0.02~\% $ \\ \hline |
tau selection & 394 & $ 53.51 \pm 0.15 ~\% $ & $ 3.70 \pm 0.02~\% $ \\ \hline |
| |
|
| \end{tabular} |
\end{tabular} |
| \caption{Preselection $t\overline{t}\rightarrow\tau+jets$ cut flow} |
\caption{Preselection $t\overline{t}\rightarrow\tau+jets$ cut flow} |
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Line 176 Electron veto & 1048 & $ 54.94 \pm 0.10
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Line 179 Electron veto & 1048 & $ 54.94 \pm 0.10
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| Muon veto & 1047 & $ 99.95 \pm 0.01 ~\% $ & $ 9.38 \pm 0.02~\% $ \\ |
Muon veto & 1047 & $ 99.95 \pm 0.01 ~\% $ & $ 9.38 \pm 0.02~\% $ \\ |
| MET selection & 1002 & $ 95.64 \pm 0.05~\% $ & $ 8.97 \pm 0.02~\% $ \\ |
MET selection & 1002 & $ 95.64 \pm 0.05~\% $ & $ 8.97 \pm 0.02~\% $ \\ |
| MET significance & 669 & $ 66.74 \pm 0.13 ~\% $ & $ 5.99 \pm 0.02~\% $ \\ |
MET significance & 669 & $ 66.74 \pm 0.13 ~\% $ & $ 5.99 \pm 0.02~\% $ \\ |
| NN tau cut & 395 & $ 59.12 \pm 0.16 ~\% $ & $ 3.54 \pm 0.02~\% $ \\ \hline |
tau selection & 395 & $ 59.12 \pm 0.16 ~\% $ & $ 3.54 \pm 0.02~\% $ \\ \hline |
| |
|
| \end{tabular} |
\end{tabular} |
| \caption{Preselection $t\overline{t}\rightarrow e+jets$ cut flow} |
\caption{Preselection $t\overline{t}\rightarrow e+jets$ cut flow} |
|
Line 200 Electron veto & 1967 & $ 99.59 \pm 0.01
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Line 203 Electron veto & 1967 & $ 99.59 \pm 0.01
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| Muon veto & 1170 & $ 59.48 \pm 0.09 ~\% $ & $ 10.48 \pm 0.02~\% $ \\ |
Muon veto & 1170 & $ 59.48 \pm 0.09 ~\% $ & $ 10.48 \pm 0.02~\% $ \\ |
| MET selection & 1127 & $ 96.31 \pm 0.04~\% $ & $ 10.09 \pm 0.02~\% $ \\ |
MET selection & 1127 & $ 96.31 \pm 0.04~\% $ & $ 10.09 \pm 0.02~\% $ \\ |
| MET significance & 812 & $ 72.06 \pm 0.11 ~\% $ & $ 7.27 \pm 0.02~\% $ \\ |
MET significance & 812 & $ 72.06 \pm 0.11 ~\% $ & $ 7.27 \pm 0.02~\% $ \\ |
| NN tau cut & 186 & $ 22.95 \pm 0.13 ~\% $ & $ 1.67 \pm 0.01~\% $ \\ \hline |
tau selection & 186 & $ 22.95 \pm 0.13 ~\% $ & $ 1.67 \pm 0.01~\% $ \\ \hline |
| |
|
| \end{tabular} |
\end{tabular} |
| \caption{Preselection $t\overline{t}\rightarrow \mu +jets$ cut flow} |
\caption{Preselection $t\overline{t}\rightarrow \mu +jets$ cut flow} |
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Line 223 Electron veto & 110 & $ 76.14 \pm 0.13
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Line 226 Electron veto & 110 & $ 76.14 \pm 0.13
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| Muon veto & 83 & $ 75.08 \pm 0.16 ~\% $ & $ 2.95 \pm 0.01~\% $ \\ |
Muon veto & 83 & $ 75.08 \pm 0.16 ~\% $ & $ 2.95 \pm 0.01~\% $ \\ |
| MET selection & 80 & $ 96.45 \pm 0.08~\% $ & $ 2.84 \pm 0.01~\% $ \\ |
MET selection & 80 & $ 96.45 \pm 0.08~\% $ & $ 2.84 \pm 0.01~\% $ \\ |
| MET significance & 60 & $ 75.32 \pm 0.19 ~\% $ & $ 2.14 \pm 0.01~\% $ \\ |
MET significance & 60 & $ 75.32 \pm 0.19 ~\% $ & $ 2.14 \pm 0.01~\% $ \\ |
| NN tau cut & 38 & $ 63.21 \pm 0.24 ~\% $ & $ 1.35 \pm 0.01~\% $ \\ \hline |
tau selection & 38 & $ 63.21 \pm 0.24 ~\% $ & $ 1.35 \pm 0.01~\% $ \\ \hline |
| |
|
| \end{tabular} |
\end{tabular} |
| \caption{Preselection $t\overline{t}\rightarrow l+l$ cut flow} |
\caption{Preselection $t\overline{t}\rightarrow l+l$ cut flow} |
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