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# Line 2 | Line 2
2   \label{sec:datadriven}
3   We have developed two data-driven methods to
4   estimate the background in the signal region.
5 < The first one explouts the fact that
6 < \met and \met$/\sqrt{\rm SumJetPt}$ are nearly
5 > The first one exploits the fact that
6 > SumJetPt and \met$/\sqrt{\rm SumJetPt}$ are nearly
7   uncorrelated for the $t\bar{t}$ background
8   (Section~\ref{sec:abcd});  the second one
9   is based on the fact that in $t\bar{t}$ the
# Line 12 | Line 12 | nearly the same as the $P_T$ of the pair
12   from $W$-decays, which is reconstructed as \met in the
13   detector.
14  
15 < In 30 pb$^{-1}$ we expect $\approx$ 1 SM event in
16 < the signal region.  The expectations from the LMO
17 < and LM1 SUSY benchmark points are 15.1 and
18 < 6.0 events respectively. {\color{red} I took these
19 < numbers from the twiki, rescaling from 11.06 to 30/pb.
20 < They seem too large...are they really right?}
15 >
16 > %{\color{red} I took these
17 > %numbers from the twiki, rescaling from 11.06 to 30/pb.
18 > %They seem too large...are they really right?}
19  
20  
21   \subsection{ABCD method}
22   \label{sec:abcd}
23  
24 < We find that in $t\bar{t}$ events \met and
25 < \met$/\sqrt{\rm SumJetPt}$ are nearly uncorrelated.
26 < This is demonstrated in Figure~\ref{fig:uncor}.
24 > We find that in $t\bar{t}$ events SumJetPt and
25 > \met$/\sqrt{\rm SumJetPt}$ are nearly uncorrelated,
26 > as demonstrated in Figure~\ref{fig:uncor}.
27   Thus, we can use an ABCD method in the \met$/\sqrt{\rm SumJetPt}$ vs
28   sumJetPt plane to estimate the background in a data driven way.
29  
30 < \begin{figure}[tb]
30 > %\begin{figure}[bht]
31 > %\begin{center}
32 > %\includegraphics[width=0.75\linewidth]{uncorrelated.pdf}
33 > %\caption{\label{fig:uncor}\protect Distributions of SumJetPt
34 > %in MC $t\bar{t}$ events for different intervals of
35 > %MET$/\sqrt{\rm SumJetPt}$.}
36 > %\end{center}
37 > %\end{figure}
38 >
39 > \begin{figure}[bht]
40   \begin{center}
41 < \includegraphics[width=0.75\linewidth]{uncorrelated.pdf}
41 > \includegraphics[width=0.75\linewidth]{uncor.png}
42   \caption{\label{fig:uncor}\protect Distributions of SumJetPt
43   in MC $t\bar{t}$ events for different intervals of
44 < MET$/\sqrt{\rm SumJetPt}$.}
44 > MET$/\sqrt{\rm SumJetPt}$. h1, h2, and h3 refer to the MET$/\sqrt{\rm SumJetPt}$
45 > intervals 4.5-6.5, 6.5-8.5 and $>$8.5, respectively.}
46   \end{center}
47   \end{figure}
48  
49 < \begin{figure}[bt]
49 > \begin{figure}[tb]
50   \begin{center}
51   \includegraphics[width=0.5\linewidth, angle=90]{abcdMC.pdf}
52 < \caption{\label{fig:abcdMC}\protect Distributions of SumJetPt
53 < vs. MET$/\sqrt{\rm SumJetPt}$ for SM Monte Carlo.  Here we also
46 < show our choice of ABCD regions. {\color{red} Derek, I
47 < do not know if this is SM or $t\bar{t}$ only.}}
52 > \caption{\label{fig:abcdMC}\protect Distributions of MET$/\sqrt{\rm SumJetPt}$ vs.
53 > SumJetPt for SM Monte Carlo.  Here we also show our choice of ABCD regions.}
54   \end{center}
55   \end{figure}
56  
# Line 53 | Line 59 | Our choice of ABCD regions is shown in F
59   The signal region is region D.  The expected number of events
60   in the four regions for the SM Monte Carlo, as well as the BG
61   prediction AC/B are given in Table~\ref{tab:abcdMC} for an integrated
62 < luminosity of 30 pb$^{-1}$.  The ABCD method is accurate
63 < to about 10\%. {\color{red} Avi wants some statement about stability
64 < wrt changes in regions.  I am not sure that we have done it and
65 < I am not sure it is necessary (Claudio).}
62 > luminosity of 35 pb$^{-1}$.  The ABCD method with chosen boundaries is accurate
63 > to about 20\%. As shown in Table~\ref{tab:abcdsyst}, we assess systematic uncertainties
64 > by varying the boundaries by an amount consistent with the hadronic energy scale uncertainty,
65 > which we take as $\pm$5\% for SumJetPt and $\pm$2.5\% for MET/$\sqrt{\rm SumJetPt}$, since the
66 > uncertainty on this quantity partially cancels due to the fact that it is a ratio of correlated
67 > quantities. Based on these studies we assess a correction factor $k_{ABCD} = 1.2 \pm 0.2$ to the
68 > predicted yield using the ABCD method.
69  
70 < \begin{table}[htb]
70 >
71 > %{\color{red} Avi wants some statement about stability
72 > %wrt changes in regions.  I am not sure that we have done it and
73 > %I am not sure it is necessary (Claudio).}
74 >
75 > \begin{table}[ht]
76   \begin{center}
77   \caption{\label{tab:abcdMC} Expected SM Monte Carlo yields for
78 < 30 pb$^{-1}$ in the ABCD regions.}
79 < \begin{tabular}{|l|c|c|c|c||c|}
78 > 35 pb$^{-1}$ in the ABCD regions, as well as the predicted yield in
79 > the signal region given by A $\times$ C / B. Here `SM other' is the sum
80 > of non-dileptonic $t\bar{t}$ decays, $W^{\pm}$+jets, $W^+W^-$,
81 > $W^{\pm}Z^0$, $Z^0Z^0$ and single top.}
82 > \begin{tabular}{lccccc}
83 > \hline
84 >         sample                          &              A   &              B   &              C   &              D   &    A $\times$ C / B \\
85 > \hline
86 >
87 >
88 > \hline
89 > $t\bar{t}\rightarrow \ell^{+}\ell^{-}$   &           7.96   &          33.07   &           4.81   &           1.20   &           1.16  \\
90 > $Z^0 \rightarrow \ell^{+}\ell^{-}$       &           0.03   &           1.47   &           0.10   &           0.10   &           0.00  \\
91 >       SM other                          &           0.65   &           2.31   &           0.17   &           0.14   &           0.05  \\
92 > \hline
93 >    total SM MC                          &           8.63   &          36.85   &           5.07   &           1.43   &           1.19  \\
94 > \hline
95 > \end{tabular}
96 > \end{center}
97 > \end{table}
98 >
99 >
100 >
101 > \begin{table}[ht]
102 > \begin{center}
103 > \caption{\label{tab:abcdsyst} Results of the systematic study of the ABCD method by varying the boundaries
104 > between the ABCD regions shown in Fig.~\ref{fig:abcdMC}. Here $x_1$ is the lower SumJetPt boundary and
105 > $x_2$ is the boundary separating regions A and B from C and D, their nominal values are 125 and 300~GeV,
106 > respectively. $y_1$ is the lower MET/$\sqrt{\rm SumJetPt}$ boundary and
107 > $y_2$ is the boundary separating regions B and C from A and D, their nominal values are 4.5 and 8.5~GeV$^{1/2}$,
108 > respectively.}
109 > \begin{tabular}{cccc|c}
110 > \hline
111 > $x_1$   &   $x_2$ & $y_1$   &   $y_2$ & Observed/Predicted \\
112 > \hline
113 > nominal & nominal & nominal & nominal & 1.20     \\
114 > +5\%    & +5\%    & +2.5\%  & +2.5\%  & 1.38     \\
115 > +5\%    & +5\%    & nominal & nominal & 1.31     \\
116 > nominal & nominal & +2.5\%  & +2.5\%  & 1.25     \\
117 > nominal & +5\%    & nominal & +2.5\%  & 1.32     \\
118 > nominal & -5\%    & nominal & -2.5\%  & 1.16     \\
119 > -5\%    & -5\%    & +2.5\%  & +2.5\%  & 1.21     \\
120 > +5\%    & +5\%    & -2.5\%  & -2.5\%  & 1.26     \\
121   \hline
67 Sample   & A   & B    & C   & D   & AC/D \\ \hline
68 ttdil    & 6.9 & 28.6 & 4.2 & 1.0 & 1.0  \\
69 Zjets    & 0.0 & 1.3  & 0.1 & 0.1 & 0.0  \\
70 Other SM & 0.5 & 2.0  & 0.1 & 0.1 & 0.0  \\ \hline
71 total MC & 7.4 & 31.9 & 4.4 & 1.2 & 1.0 \\ \hline
122   \end{tabular}
123   \end{center}
124   \end{table}
# Line 89 | Line 139 | In practice one has to rescale the resul
139   to account for the fact that any dilepton selection must include a
140   moderate \met cut in order to reduce Drell Yan backgrounds.  This
141   is discussed in Section 5.3 of Reference~\cite{ref:ourvictory}; for a \met
142 < cut of 50 GeV, the rescaling factor is obtained from the data as
142 > cut of 50 GeV, the rescaling factor is obtained from the MC as
143  
144   \newcommand{\ptll} {\ensuremath{P_T(\ell\ell)}}
145   \begin{center}
# Line 98 | Line 148 | $ K = \frac{\int_0^{\infty} {\cal N}(\pt
148  
149  
150   Monte Carlo studies give values of $K$ that are typically between 1.5 and 1.6,
151 < depending on selection details.
151 > depending on selection details.  
152 > %%%TO BE REPLACED
153 > %Given the integrated luminosity of the
154 > %present dataset, the determination of $K$ in data is severely statistics
155 > %limited.  Thus, we take $K$ from $t\bar{t}$ Monte Carlo as
156 >
157 > %\begin{center}
158 > %$ K_{MC} = \frac{\int_0^{\infty} {\cal N}(\met)~~d\met~}{\int_{50}^{\infty} {\cal N}(\met)~~d\met~}$
159 > %\end{center}
160 >
161 > %\noindent {\color{red} For the 11 pb result we have used $K$ from data.}
162  
163   There are several effects that spoil the correspondance between \met and
164   $P_T(\ell\ell)$:
165   \begin{itemize}
166   \item $Ws$ in top events are polarized.  Neutrinos are emitted preferentially
167 < forward in the $W$ rest frame, thus the $P_T(\nu\nu)$ distribution is harder
167 > parallel to the $W$ velocity while charged leptons are emitted prefertially
168 > anti-parallel. Thus the $P_T(\nu\nu)$ distribution is harder
169   than the $P_T(\ell\ell)$ distribution for top dilepton events.
170   \item The lepton selections results in $P_T$ and $\eta$ cuts on the individual
171   leptons that have no simple correspondance to the neutrino requirements.
172   \item Similarly, the \met$>$50 GeV cut introduces an asymmetry between leptons and
173   neutrinos which is only partially compensated by the $K$ factor above.
174   \item The \met resolution is much worse than the dilepton $P_T$ resolution.
175 < When convoluted with a falling spectrum in the tails of \met, this result
175 > When convoluted with a falling spectrum in the tails of \met, this results
176   in a harder spectrum for \met than the original $P_T(\nu\nu)$.
177   \item The \met response in CMS is not exactly 1.  This causes a distortion
178   in the \met distribution that is not present in the $P_T(\ell\ell)$ distribution.
# Line 122 | Line 183 | of $P_T(\ell\ell)$ and $P_T(\nu\nu)$ do
183   sources.  These events can affect the background prediction.  Particularly
184   dangerous are high $P_T$ Drell Yan events that barely pass the \met$>$ 50
185   GeV selection.  They will tend to push the data-driven background prediction up.
186 + Therefore we estimate the number of DY events entering the background prediction
187 + using the $R_{out/in}$ method as described in Sec.~\ref{sec:othBG}.
188   \end{itemize}
189  
190   We have studied these effects in SM Monte Carlo, using a mixture of generator and
# Line 134 | Line 197 | The results are summarized in Table~\ref
197   \begin{center}
198   \caption{\label{tab:victorybad} Test of the data driven method in Monte Carlo
199   under different assumptions.  See text for details.}
200 < \begin{tabular}{|l|c|c|c|c|c|c|c|}
200 > \begin{tabular}{|l|c|c|c|c|c|c|c|c|}
201   \hline
202 < & True $t\bar{t}$ dilepton & $t\to W\to\tau$& other SM & GEN or  & Lepton $P_T$    & \met $>$ 50& obs/pred \\
203 < & included                 & included  & included & RECOSIM & and $\eta$ cuts &      &     \\ \hline
204 < 1&Y                        &     N     &   N      &  GEN    &   N             &   N  &       \\
205 < 2&Y                        &     N     &   N      &  GEN    &   Y             &   N  &   \\
206 < 3&Y                        &     N     &   N      &  GEN    &   Y             &   Y  &   \\
207 < 4&Y                        &     N     &   N      & RECOSIM &   Y             &   Y  &   \\
208 < 5&Y                        &     Y     &   N      & RECOSIM &   Y             &   Y  &   \\
209 < 6&Y                        &     Y     &   Y      & RECOSIM &   Y             &   Y  &   \\
202 > & True $t\bar{t}$ dilepton & $t\to W\to\tau$& other SM & GEN or  & Lepton $P_T$    & Z veto & \met $>$ 50& obs/pred \\
203 > & included                 & included       & included & RECOSIM & and $\eta$ cuts &        &            &  \\ \hline
204 > 1&Y                        &     N          &   N      &  GEN    &   N             &   N    & N          & 1.90  \\
205 > 2&Y                        &     N          &   N      &  GEN    &   Y             &   N    & N          & 1.64  \\
206 > 3&Y                        &     N          &   N      &  GEN    &   Y             &   Y    & N          & 1.59  \\
207 > 4&Y                        &     N          &   N      &  GEN    &   Y             &   Y    & Y          & 1.55  \\
208 > 5&Y                        &     N          &   N      & RECOSIM &   Y             &   Y    & Y          & 1.51  \\
209 > 6&Y                        &     Y          &   N      & RECOSIM &   Y             &   Y    & Y          & 1.58  \\
210 > 7&Y                        &     Y          &   Y      & RECOSIM &   Y             &   Y    & Y          & 1.38  \\
211 > %%%NOTE: updated value 1.18 -> 1.46 since 2/3 DY events have been removed by updated analysis selections,
212 > %%%dpt/pt cut and general lepton veto
213   \hline
214   \end{tabular}
215   \end{center}
# Line 155 | Line 221 | line of Table~\ref{tab:victorybad}, {\em
221   cuts.  We have verified that this effect is due to the polarization of
222   the $W$ (we remove the polarization by reweighting the events and we get
223   good agreement between prediction and observation).  The kinematical
224 < requirements (lines 2 and 3) do not have a significant additional effect.
225 < Going from GEN to RECOSIM there is a significant change in observed/predicted.  
226 < We have tracked this down to the fact that tcMET underestimates the true \met
227 < by $\approx 4\%$\footnote{We find that observed/predicted changes by roughly 0.1
228 < for each 1.5\% change in \met response.}.  Finally, contamination from non $t\bar{t}$
229 < events can have a significant impact on the BG prediction.  The changes between
230 < lines 5 and 6 of Table~\ref{tab:victorybad} is driven by only {\color{red} 3}
231 < Drell Yan events that pass the \met selection.
224 > requirements (lines 2,3,4) compensate somewhat for the effect of W polarization.
225 > Going from GEN to RECOSIM, the change in observed/predicted is small.  
226 > % We have tracked this down to the fact that tcMET underestimates the true \met
227 > % by $\approx 4\%$\footnote{We find that observed/predicted changes by roughly 0.1
228 > %for each 1.5\% change in \met response.}.  
229 > Finally, contamination from non $t\bar{t}$
230 > events can have a significant impact on the BG prediction.  
231 > %The changes between
232 > %lines 6 and 7 of Table~\ref{tab:victorybad} is driven by 3
233 > %Drell Yan events that pass the \met selection in Monte Carlo (thus the effect
234 > %is statistically not well quantified).
235  
236   An additional source of concern is that the CMS Madgraph $t\bar{t}$ MC does
237   not include effects of spin correlations between the two top quarks.  
238   We have studied this effect at the generator level using Alpgen.  We find
239 < that the bias is a the few percent level.
239 > that the bias is at the few percent level.
240 >
241 > %%%TO BE REPLACED
242 > %Based on the results of Table~\ref{tab:victorybad}, we conclude that the
243 > %naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to
244 > %be corrected by a factor of {\color{red} $ K_{\rm{fudge}} =1.2 \pm 0.3$
245 > %(We still need to settle on thie exact value of this.
246 > %For the 11 pb analysis it is taken as =1.)} . The quoted
247 > %uncertainty is based on the stability of the Monte Carlo tests under
248 > %variations of event selections, choices of \met algorithm, etc.
249 > %For example, we find that observed/predicted changes by roughly 0.1
250 > %for each 1.5\% change in the average \met response.  
251  
252   Based on the results of Table~\ref{tab:victorybad}, we conclude that the
253 < naive data driven background estimate based on $P_T{\ell\ell)}$ needs to
254 < be corrected by a factor of {\color{red} $1.4 \pm 0.3$  (We need to
255 < decide what this number should be)}.  The quoted
256 < uncertainty is based on the stability of the Monte Carlo tests under
253 > naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to
254 > be corrected by a factor of $ K_C = X \pm Y$.
255 > The value of this correction factor as well as the systematic uncertainty
256 > will be assessed using 38X ttbar madgraph MC. In the following we use
257 > $K_C = 1$ for simplicity. Based on previous MC studies we foresee a correction
258 > factor of $K_C \approx 1.2 - 1.5$, and we will assess an uncertainty
259 > based on the stability of the Monte Carlo tests under
260   variations of event selections, choices of \met algorithm, etc.
261 + For example, we find that observed/predicted changes by roughly 0.1
262 + for each 1.5\% change in the average \met response.
263 +
264  
265  
266   \subsection{Signal Contamination}
267   \label{sec:sigcont}
268  
269 < All data-driven methods are principle subject to signal contaminations
269 > All data-driven methods are in principle subject to signal contaminations
270   in the control regions, and the methods described in
271   Sections~\ref{sec:abcd} and~\ref{sec:victory} are not exceptions.
272   Signal contamination tends to dilute the significance of a signal
# Line 193 | Line 279 | adds redundancy because signal contamina
279   in the different control regions for the two methods.
280   For example, in the extreme case of a
281   new physics signal
282 < with $P_T(\ell \ell) = \met$, an excess of ev ents would be seen
282 > with $P_T(\ell \ell) = \met$, an excess of events would be seen
283   in the ABCD method but not in the $P_T(\ell \ell)$ method.
284  
285  
286   The LM points are benchmarks for SUSY analyses at CMS.  The effects
287   of signal contaminations for a couple such points are summarized
288 < in Table~\ref{tab:sigcontABCD} and~\ref{tab:sigcontPT}.
203 < Signal contamination is definitely an important
288 > in Table~\ref{tab:sigcont}. Signal contamination is definitely an important
289   effect for these two LM points, but it does not totally hide the
290   presence of the signal.
291  
292  
293   \begin{table}[htb]
294   \begin{center}
295 < \caption{\label{tab:sigcontABCD} Effects of signal contamination
296 < for the background predictions of the ABCD method including LM0 or
297 < LM1.  Results
298 < are normalized to 30 pb$^{-1}$.}
299 < \begin{tabular}{|c||c|c||c|c|}
215 < \hline
216 < SM         & LM0         & BG Prediction & LM1          & BG Prediction \\
217 < Background & Contribution& Including LM0 & Contribution & Including LM1  \\ \hline
218 < x          & x           & x             & x            & x \\
295 > \caption{\label{tab:sigcont} Effects of signal contamination
296 > for the two data-driven background estimates. The three columns give
297 > the expected yield in the signal region and the background estimates
298 > using the ABCD and $P_T(\ell \ell)$ methods. Results are normalized to 35~pb$^{-1}$.}
299 > \begin{tabular}{lccc}
300   \hline
301 < \end{tabular}
302 < \end{center}
303 < \end{table}
304 <
305 < \begin{table}[htb]
225 < \begin{center}
226 < \caption{\label{tab:sigcontPT} Effects of signal contamination
227 < for the background predictions of the $P_T(\ell\ell)$ method including LM0 or
228 < LM1.  Results
229 < are normalized to 30 pb$^{-1}$.}
230 < \begin{tabular}{|c||c|c||c|c|}
231 < \hline
232 < SM         & LM0         & BG Prediction & LM1          & BG Prediction \\
233 < Background & Contribution& Including LM0 & Contribution & Including LM1  \\ \hline
234 < x          & x           & x             & x            & x \\
301 >            &      Yield      &      ABCD    & $P_T(\ell \ell)$  \\
302 > \hline
303 > SM only     &      1.43       &      1.19    &             1.03  \\
304 > SM + LM0    &      7.90       &      4.23    &             2.35  \\
305 > SM + LM1    &      4.00       &      1.53    &             1.51  \\
306   \hline
307   \end{tabular}
308   \end{center}
309   \end{table}
310  
311 +
312 +
313 + %\begin{table}[htb]
314 + %\begin{center}
315 + %\caption{\label{tab:sigcontABCD} Effects of signal contamination
316 + %for the background predictions of the ABCD method including LM0 or
317 + %LM1.  Results
318 + %are normalized to 30 pb$^{-1}$.}
319 + %\begin{tabular}{|c|c||c|c||c|c|}
320 + %\hline
321 + %SM         & BG Prediction  & SM$+$LM0     & BG Prediction & SM$+$LM1     & BG Prediction \\
322 + %Background & SM Only        & Contribution & Including LM0 & Contribution & Including LM1  \\ \hline
323 + %1.2        & 1.0            & 6.8          & 3.7           & 3.4          & 1.3 \\
324 + %\hline
325 + %\end{tabular}
326 + %\end{center}
327 + %\end{table}
328 +
329 + %\begin{table}[htb]
330 + %\begin{center}
331 + %\caption{\label{tab:sigcontPT} Effects of signal contamination
332 + %for the background predictions of the $P_T(\ell\ell)$ method including LM0 or
333 + %LM1.  Results
334 + %are normalized to 30 pb$^{-1}$.}
335 + %\begin{tabular}{|c|c||c|c||c|c|}
336 + %\hline
337 + %SM         & BG Prediction  & SM$+$LM0     & BG Prediction & SM$+$LM1     & BG Prediction \\
338 + %Background & SM Only        & Contribution & Including LM0 & Contribution & Including LM1  \\ \hline
339 + %1.2        & 1.0            & 6.8          & 2.2           & 3.4          & 1.5 \\
340 + %\hline
341 + %\end{tabular}
342 + %\end{center}
343 + %\end{table}
344 +

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