Annotation of ttbar/p20_taujets_note/Strategy_and_Dataset.tex, revision 1.1.1.1
1.1 uid12904 1:
2: \section{Strategy}
3:
4:
5: \subsection{\label{sub:Signal-characteristics}Signal characteristics}
6:
7:
8: \subsubsection{Parton level MC}
9:
10: First of all we want to examine the properties of our signal. For
11: these purposes we used MC simulated samples (\textasciitilde{}10K
12: events each) generated with ALPGEN \cite{ALPGEN} interfaced to Pythia
13: \cite{PYTHIA} for showering and fragmentation.
14:
15:
16: \paragraph{$t\bar{t}$}
17:
18: First of all we wanted to look at the properties of the top quark
19: itself. Figure \ref{t-jets} shows the $\eta$, $\phi$ and $P_{T}$
20: distributions.
21:
22: %
23: \begin{figure}
24: \subfigure[$P_{T}$ of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_tjets}}\subfigure[$\eta$ of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_tjets}}
25:
26: \subfigure[$\phi$ of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/phi_tjets}}
27:
28:
29: \caption{Properties of t-quarks at the parton level in signal MC sample, $P_{T}$>
30: 15 GeV}
31:
32: \begin{centering}\label{t-jets}\par\end{centering}
33: \end{figure}
34:
35:
36:
37: \paragraph{$\tau$ and $\not\!\! E_{T}$}
38:
39: The unique property of $\tau$ (compared to other leptons) is that
40: it emits neutrino in its decay before it even reaches detector volume,
41: contributing to the missing energy of the event. For this reason the
42: $\tau$, available for measurement is not the same as physical $\tau$
43: produced. Figure \ref{cap:MC taus} demonstrates how a sizable fraction
44: of $\tau$ momentum goes missing. The plots of $\tau$ $\eta$ (Figure
45: \ref{cap:MC taus}) and transverse mass with $\not\!\! E_{T}$ thus
46: are done for the visible part of $\tau$
47:
48: This is to be compared with the $e+jets$ channel (Figure \ref{cap:MC elecs}).
49: As one can observe, the {}``total'' $\tau$ leptons behave very
50: simmilar to electrons, as of cause expected. However, after taking
51: into account the lost part of the $\tau$ energy situation becomes
52: very different.
53:
54: %
55: \begin{figure}
56: \subfigure[Parton level $\not E_{T}$ for the signal MC (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/met_mc}}
57: \subfigure[mT of MC $\tau$ and $\not E_{T} $ (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/mt_tau_met_mc}}
58:
59: \subfigure[$\eta$ of the MC $\tau$ in signal MC (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_tau_mc}}
60: \subfigure[$P_{T}$ of the MC $\tau$ in signal MC (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_tau_mc}}
61:
62: \subfigure[Visible energy fraction of $\tau$ in signal MC]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/visable_fraction}}
63:
64:
65: \caption{Properties of $\not\!\! E_{T}$ and $\tau$ at the parton level in
66: signal MC sample}
67:
68: \begin{centering}\label{cap:MC taus}\par\end{centering}
69: \end{figure}
70:
71:
72: %
73: \begin{figure}
74: \subfigure[Parton level $\not E_{T}$ for the signal MC (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/met_mc_elec}}
75: \subfigure[mT of MC electron and $\not E_{T} $ (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/mt_tau_met_mc_elec}}
76:
77: \subfigure[$\eta$ of the MC electron in signal MC (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_tau_mc_elec}}
78: \subfigure[$P_{T}$ of the MC electron in signal MC (red is total, green- visible)]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_tau_mc_elec}}
79:
80:
81: \caption{Properties of $\not\!\! E_{T}$ and electron at the parton level
82: in $t\bar{t}\rightarrow e+jets$ MC sample}
83:
84: \begin{centering}\label{cap:MC elecs}\par\end{centering}
85: \end{figure}
86:
87:
88:
89: \paragraph{Jets}
90:
91: b - jets are shown on Figure \ref{b-jets} while the product of W
92: decay are shown on Figure \ref{not b-jets}. This however doesn't
93: account for all the jets that will be reconstructed. Figure \ref{not b-jets-all}
94: demonstrates all the non-b quarks and gluons in a $t\bar{t}$ event.
95:
96: %
97: \begin{figure}
98: \subfigure[Number of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/nbquarks}}
99: \subfigure[$P_{T}$ of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_bjets}}
100:
101: \subfigure[$\eta$ of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_bjets}}
102: \subfigure[$\phi$ of b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/phi_bjets}}
103:
104:
105: \caption{Properties of b-quarks at the parton level in signal MC sample, $P_{T}$>
106: 15 GeV}
107:
108: \begin{centering}\label{b-jets}\par\end{centering}
109: \end{figure}
110:
111:
112: %
113: \begin{figure}
114: \subfigure[Number of light quarks from the W decay]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/nlightquarks}}
115: \subfigure[$P_{T}$ of light quarks from the W decay]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_notbjets}}
116:
117: \subfigure[$\eta$ of light quarks from the W decay]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_notbjets}}
118: \subfigure[$\phi$ of light quarks from the W decay]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/phi_notbjets}}
119:
120:
121: \caption{Properties of light quarks from the W decay at the parton level in
122: signal MC sample, $P_{T}$> 15 GeV}
123:
124: \begin{centering}\label{not b-jets}\par\end{centering}
125: \end{figure}
126:
127:
128: %
129: \begin{figure}
130: \subfigure[Number of not b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/nlightquarks_all}}
131: \subfigure[$P_{T}$ of not b-quarks]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_notbjets_all}}
132:
133: \subfigure[$\eta$ of not b-quarks ]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_notbjets_all}}
134: \subfigure[$\phi$ of not b-quarks ]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/phi_notbjets_all}}
135:
136:
137: \caption{Properties of all the light quarks and gluons in an event at the
138: parton level in signal MC sample, $P_{T}$> 15 GeV}
139:
140: \begin{centering}\label{not b-jets-all}\par\end{centering}
141: \end{figure}
142:
143:
144:
145: \subsubsection{Detector signature (reconstructed Monte Carlo)}
146:
147: Now we need to find out how well our experiment observes and reconstructs
148: this physical process. The $t\bar{t}\rightarrow\tau+jets$ Monte Carlo
149: file was processed through the detailed D0 Detector simulation. Jets
150: are reconstructed, using 0.5 radius cone (in $\eta-\phi$). Taus are
151: identified using tau ID algorithm and we apply 0.8 cut on the $\tau$
152: selection neural net (section \ref{sub:tau--ID}).
153:
154:
155: \paragraph{$\tau$ and $\not\!\! E_{T}$}
156:
157: We can see that for reconstructed $\tau$'s $mT(of$ $\tau$ $and$
158: $\not E_{T})$ (Figure \ref{cap:reco tau}) doesn't look as good as
159: for MC taus (Figure \ref{cap:MC taus}). We observe a noticeable \char`\"{}tail\char`\"{}
160: above 80 GeV.
161:
162: %
163: \begin{figure}
164: \subfigure[Reconstructed $\not E_{T}$ for the signal MC ]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/met_reco}}
165: \subfigure[mT of MC $\tau$ and $\not E_{T} $ reconstructed ]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/mt_tau_met_reco}}
166:
167: \subfigure[$\eta$ of the MC tau in signal MC reconstructed ]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_tau_reco}}
168: \subfigure[ $P_{T}$ of the $\tau$ ]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/pt_tau_reco}}
169:
170:
171: \caption{Properties of detector reconstructed $\not\!\! E_{T}$ and $\tau$
172: in signal MC sample}
173:
174: \begin{centering}\label{cap:reco tau}\par\end{centering}
175: \end{figure}
176:
177:
178:
179: \paragraph{Jets}
180:
181: Before b-tagging (section \ref{sub:B-tagging}) one can't separate
182: b-jets from non-b jets, so we don't make a distinction at this point.
183: Most important variables are the number of jets and $\eta$ and $P_{T}$
184: distributions (Figure \ref{jets1}).
185:
186: %
187: \begin{figure}
188: \subfigure[Number of jets]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/njets}}
189: \subfigure[$P_{T}$ of jets]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/jetpt}}
190:
191: \subfigure[$\eta$ of jets]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/eta_jets}}
192: \subfigure[$\phi$ of jets]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/phi_jets}}
193:
194:
195: \caption{Properties of the jets in signal MC sample, $P_{T}$> 15 GeV}
196:
197: \begin{centering}\label{jets1}\par\end{centering}
198: \end{figure}
199:
200:
201: Jets are arranged in the order of their $P_{T}$: leading (highest),
202: sub-leading etc. We can see on Figure \ref{jets1} that we typically
203: have 4 or 5 jets in an event. It is interesting to compare the leading
204: jet to the fourth and fifth jets (Figure \ref{jets2}). We can see
205: that jets after the third are very soft, as expected.
206:
207: %
208: \begin{figure}
209: \subfigure[1st jet]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/jet0pt}}
210: \subfigure[2nd jet]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/jet1pt}}
211:
212: \subfigure[3rd jet]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/jet2pt}}
213: \subfigure[4th jet]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/jet3pt}}
214:
215: \subfigure[5th jet]{\includegraphics[scale=0.3]{MS_thesis/proposal_plots/jet4pt}}
216:
217:
218: \caption{$P_{T}$ distributions for jets in signal MC sample (including $\tau$)}
219:
220: \begin{centering}\label{jets2}\par\end{centering}
221: \end{figure}
222:
223:
224:
225: \subsection{Backgrounds}
226:
227: Two main distinctive features of the signal limit the spectrum of
228: important backgrounds. In order to be relevant the process must have
229: high (>3) number of jets as well as sizable (>15 GeV) $\not\!\! E_{T}$.
230: All the candidate processes are listed in Table \ref{backgrounds}.
231: The cross section listed include the branching fractions into $\tau$
232:
233: We can conclude that two dominant background sources are QCD ({}``fake
234: $\tau$'') and W+4jets. These two sources were taken into account
235: in these analysis.
236:
237: %
238: \begin{table}
239: \begin{tabular}{|l|l|c|}
240: \hline
241: \multicolumn{1}{||l|}{Background}&
242: \multicolumn{1}{||l|}{Description}&
243: \multicolumn{1}{||l||}{Cross Section}\tabularnewline
244: \hline
245: $W+jjjj\rightarrow\tau\nu jjjj$&
246: Has identical signature to the signal&
247: $\sim$18 pb \tabularnewline
248: \hline
249: $Z/\gamma+jjj\rightarrow\tau\tau jjj$ &
250: $\tau$ is usually found as a jet&
251: $\sim$2.6 pb\tabularnewline
252: \hline
253: $WZ\rightarrow\tau\nu jj$&
254: needs two extra jet (can be gluon emission) &
255: $\sim$0.2 pb\tabularnewline
256: \hline
257: $WW\rightarrow\tau\nu jj$&
258: needs two extra jet (can be gluon emission) &
259: $\sim$0.5 pb\tabularnewline
260: \hline
261: single top &
262: small cross section, but has b-jets &
263: $\sim$0.5 pb\tabularnewline
264: \hline
265: QCD &
266: Any 4-jet event, that doesn't have a real $\tau$ in it&
267: $>$100 nb \tabularnewline
268: \hline
269: \end{tabular}\centering
270:
271:
272: \caption{Background sources, relevant for the $\tau+jets$ analysis. Branching
273: into hadronic $\tau$ had been applied \cite{l+jets}}
274:
275: \label{backgrounds}
276: \end{table}
277:
278:
279:
280: \section{Dataset}
281:
282: As will be demonstrated in section \ref{sub:Running-trigsim} the
283: optimal (that is most efficient) combination of triggers for this
284: analysis is:
285:
286: \begin{itemize}
287: \item The Higgs Missing $H_{T}$ trigger (MHT30\_3CJT5)
288: \item The ALLJET trigger (4JT10)
289: \end{itemize}
290: Together they yield over 85\% signal acceptance and they'd been running
291: unprescaled for most of D0 stable operation.
292:
293: The data skim, utilizing both of these triggers would be optimal for
294: this analysis. Until the technical issues involved in its production
295: are fully resolved, we are using the ALLJET skim \cite{Luminosity},
296: which only contains the data, collected by the 4JT10 (and its subsequent
297: versions).
298:
299: Such skim is only 70\% efficient for the signal, but it's the closest
300: available for our needs at the moment. The full PASS2 ALLJET skim
301: had been processed through the standard D0 top group data quality
302: criteria, discarding bad luminosity blocks, at the same time computing
303: the recorded lumi. The results are represented in table \ref{lumi1}.
304: Therefore the total luminosity available for the analysis amounts
305: to $349\pm23$ $pb^{-1}$ \cite{alljet}
306:
307: %
308: \begin{table}
309: \begin{tabular}{|c|c|c|c|}
310: \hline
311: Stage&
312: Luminosity ($pb^{-1})$&
313: Relative Size (\%)&
314: Absolute Size (\%)\tabularnewline
315: \hline
316: \hline
317: Delivered&
318: 482.6&
319: 100&
320: 100\tabularnewline
321: \hline
322: Recorded&
323: 411.6&
324: 85.3&
325: 85.3\tabularnewline
326: \hline
327: Good&
328: 352.5&
329: 85.6&
330: 73.0\tabularnewline
331: \hline
332: Reconstructed&
333: 349.3&
334: 99.1&
335: 72.4\tabularnewline
336: \hline
337: \end{tabular}
338:
339:
340: \caption{The results of luminosity calculation for the PASS2 ALLJET top skim}
341:
342: \label{lumi1}
343: \end{table}
344:
345:
346: The table \ref{lumi2} demonstrates the breakdown of this luminosity
347: between the different trigger versions.
348:
349: %
350: \begin{table}
351: \begin{tabular}{|c|c|c|}
352: \hline
353: Trigger version&
354: Trigger name&
355: Luminosity ($pb^{-1})$\tabularnewline
356: \hline
357: \hline
358: 8.0&
359: 4JT10&
360: 19.4\tabularnewline
361: \hline
362: 9.0&
363: 4JT10&
364: 21.2\tabularnewline
365: \hline
366: 10.0&
367: 4JT10&
368: 15.1\tabularnewline
369: \hline
370: 11.0&
371: 4JT10&
372: 57.3\tabularnewline
373: \hline
374: 12.0&
375: 4JT12&
376: 196\tabularnewline
377: \hline
378: 13.0&
379: JT2\_4JT12L\_HT&
380: 13.5\tabularnewline
381: \hline
382: 13.1&
383: JT2\_4JT12L\_HT&
384: 27.8\tabularnewline
385: \hline
386: 13.3&
387: JT2\_4JT12L\_HT&
388: 0\tabularnewline
389: \hline
390: \end{tabular}
391:
392:
393: \caption{Luminosity of the ALLJET skim for different D0 trigger list versions}
394:
395: \label{lumi2}
396: \end{table}
397:
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