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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\%.
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 > $t\bar{t}\rightarrow \ell^{+}\ell^{-}$         &   7.96  $\pm$  0.17   &  33.07  $\pm$  0.35   &   4.81  $\pm$  0.13   &   1.20  $\pm$  0.07   &   1.16  $\pm$  0.04  \\
87 > $Z^0 \rightarrow \ell^{+}\ell^{-}$             &   0.03  $\pm$  0.03   &   1.47  $\pm$  0.38   &   0.10  $\pm$  0.10   &   0.10  $\pm$  0.10   &   0.00  $\pm$  0.00  \\
88 >            SM other                           &   0.65  $\pm$  0.06   &   2.31  $\pm$  0.13   &   0.17  $\pm$  0.03   &   0.14  $\pm$  0.03   &   0.05  $\pm$  0.01  \\
89 > \hline
90 >         total SM MC                           &   8.63  $\pm$  0.18   &  36.85  $\pm$  0.53   &   5.07  $\pm$  0.17   &   1.43  $\pm$  0.12   &   1.19  $\pm$  0.05  \\
91 > \hline
92 > \end{tabular}
93 > \end{center}
94 > \end{table}
95 >
96 >
97 >
98 > \begin{table}[ht]
99 > \begin{center}
100 > \caption{\label{tab:abcdsyst} Results of the systematic study of the ABCD method by varying the boundaries
101 > between the ABCD regions shown in Fig.~\ref{fig:abcdMC}. Here $x_1$ is the lower SumJetPt boundary and
102 > $x_2$ is the boundary separating regions A and B from C and D, their nominal values are 125 and 300~GeV,
103 > respectively. $y_1$ is the lower MET/$\sqrt{\rm SumJetPt}$ boundary and
104 > $y_2$ is the boundary separating regions B and C from A and D, their nominal values are 4.5 and 8.5~GeV$^{1/2}$,
105 > respectively.}
106 > \begin{tabular}{cccc|c}
107 > \hline
108 > $x_1$   &   $x_2$ & $y_1$   &   $y_2$ & Observed/Predicted \\
109 > \hline
110 > nominal & nominal & nominal & nominal & $1.20 \pm 0.12$    \\
111 > +5\%    & +5\%    & +2.5\%  & +2.5\%  & $1.38 \pm 0.15$    \\
112 > +5\%    & +5\%    & nominal & nominal & $1.31 \pm 0.14$    \\
113 > nominal & nominal & +2.5\%  & +2.5\%  & $1.25 \pm 0.13$    \\
114 > nominal & +5\%    & nominal & +2.5\%  & $1.32 \pm 0.14$    \\
115 > nominal & -5\%    & nominal & -2.5\%  & $1.16 \pm 0.09$    \\
116 > -5\%    & -5\%    & +2.5\%  & +2.5\%  & $1.21 \pm 0.11$    \\
117 > +5\%    & +5\%    & -2.5\%  & -2.5\%  & $1.26 \pm 0.12$    \\
118   \hline
65 Sample   & A   & B    & C   & D   & AC/D \\ \hline
66 ttdil    & 6.9 & 28.6 & 4.2 & 1.0 & 1.0  \\
67 Zjets    & 0.0 & 1.3  & 0.1 & 0.1 & 0.0  \\
68 Other SM & 0.5 & 2.0  & 0.1 & 0.1 & 0.0  \\ \hline
69 total MC & 7.4 & 31.9 & 4.4 & 1.2 & 1.0 \\ \hline
119   \end{tabular}
120   \end{center}
121   \end{table}
# Line 87 | Line 136 | In practice one has to rescale the resul
136   to account for the fact that any dilepton selection must include a
137   moderate \met cut in order to reduce Drell Yan backgrounds.  This
138   is discussed in Section 5.3 of Reference~\cite{ref:ourvictory}; for a \met
139 < cut of 50 GeV, the rescaling factor is obtained from the data as
139 > cut of 50 GeV, the rescaling factor is obtained from the MC as
140  
141   \newcommand{\ptll} {\ensuremath{P_T(\ell\ell)}}
142   \begin{center}
# Line 96 | Line 145 | $ K = \frac{\int_0^{\infty} {\cal N}(\pt
145  
146  
147   Monte Carlo studies give values of $K$ that are typically between 1.5 and 1.6,
148 < depending on selection details.
148 > depending on selection details.  
149 > %%%TO BE REPLACED
150 > %Given the integrated luminosity of the
151 > %present dataset, the determination of $K$ in data is severely statistics
152 > %limited.  Thus, we take $K$ from $t\bar{t}$ Monte Carlo as
153 >
154 > %\begin{center}
155 > %$ K_{MC} = \frac{\int_0^{\infty} {\cal N}(\met)~~d\met~}{\int_{50}^{\infty} {\cal N}(\met)~~d\met~}$
156 > %\end{center}
157 >
158 > %\noindent {\color{red} For the 11 pb result we have used $K$ from data.}
159  
160   There are several effects that spoil the correspondance between \met and
161   $P_T(\ell\ell)$:
162   \begin{itemize}
163   \item $Ws$ in top events are polarized.  Neutrinos are emitted preferentially
164 < forward in the $W$ rest frame, thus the $P_T(\nu\nu)$ distribution is harder
164 > parallel to the $W$ velocity while charged leptons are emitted prefertially
165 > anti-parallel. Thus the $P_T(\nu\nu)$ distribution is harder
166   than the $P_T(\ell\ell)$ distribution for top dilepton events.
167   \item The lepton selections results in $P_T$ and $\eta$ cuts on the individual
168   leptons that have no simple correspondance to the neutrino requirements.
169   \item Similarly, the \met$>$50 GeV cut introduces an asymmetry between leptons and
170   neutrinos which is only partially compensated by the $K$ factor above.
171   \item The \met resolution is much worse than the dilepton $P_T$ resolution.
172 < When convoluted with a falling spectrum in the tails of \met, this result
172 > When convoluted with a falling spectrum in the tails of \met, this results
173   in a harder spectrum for \met than the original $P_T(\nu\nu)$.
174   \item The \met response in CMS is not exactly 1.  This causes a distortion
175   in the \met distribution that is not present in the $P_T(\ell\ell)$ distribution.
# Line 120 | Line 180 | of $P_T(\ell\ell)$ and $P_T(\nu\nu)$ do
180   sources.  These events can affect the background prediction.  Particularly
181   dangerous are high $P_T$ Drell Yan events that barely pass the \met$>$ 50
182   GeV selection.  They will tend to push the data-driven background prediction up.
183 + Therefore we estimate the number of DY events entering the background prediction
184 + using the $R_{out/in}$ method as described in Sec.~\ref{sec:othBG}.
185   \end{itemize}
186  
187   We have studied these effects in SM Monte Carlo, using a mixture of generator and
# Line 132 | Line 194 | The results are summarized in Table~\ref
194   \begin{center}
195   \caption{\label{tab:victorybad} Test of the data driven method in Monte Carlo
196   under different assumptions.  See text for details.}
197 < \begin{tabular}{|l|c|c|c|c|c|c|c|}
197 > \begin{tabular}{|l|c|c|c|c|c|c|c|c|}
198   \hline
199 < & True $t\bar{t}$ dilepton & $t\to W\to\tau$& other SM & GEN or  & Lepton $P_T$    & \met $>$ 50& obs/pred \\
200 < & included                 & included  & included & RECOSIM & and $\eta$ cuts &      &     \\ \hline
201 < 1&Y                        &     N     &   N      &  GEN    &   N             &   N  &       \\
202 < 2&Y                        &     N     &   N      &  GEN    &   Y             &   N  &   \\
203 < 3&Y                        &     N     &   N      &  GEN    &   Y             &   Y  &   \\
204 < 4&Y                        &     N     &   N      & RECOSIM &   Y             &   Y  &   \\
205 < 5&Y                        &     Y     &   N      & RECOSIM &   Y             &   Y  &   \\
206 < 6&Y                        &     Y     &   Y      & RECOSIM &   Y             &   Y  &   \\
199 > & True $t\bar{t}$ dilepton & $t\to W\to\tau$& other SM & GEN or  & Lepton $P_T$    & Z veto & \met $>$ 50& obs/pred \\
200 > & included                 & included       & included & RECOSIM & and $\eta$ cuts &        &            &  \\ \hline
201 > 1&Y                        &     N          &   N      &  GEN    &   N             &   N    & N          & 1.90  \\
202 > 2&Y                        &     N          &   N      &  GEN    &   Y             &   N    & N          & 1.64  \\
203 > 3&Y                        &     N          &   N      &  GEN    &   Y             &   Y    & N          & 1.59  \\
204 > 4&Y                        &     N          &   N      &  GEN    &   Y             &   Y    & Y          & 1.55  \\
205 > 5&Y                        &     N          &   N      & RECOSIM &   Y             &   Y    & Y          & 1.51  \\
206 > 6&Y                        &     Y          &   N      & RECOSIM &   Y             &   Y    & Y          & 1.58  \\
207 > 7&Y                        &     Y          &   Y      & RECOSIM &   Y             &   Y    & Y          & 1.38  \\
208 > %%%NOTE: updated value 1.18 -> 1.46 since 2/3 DY events have been removed by updated analysis selections,
209 > %%%dpt/pt cut and general lepton veto
210   \hline
211   \end{tabular}
212   \end{center}
# Line 153 | Line 218 | line of Table~\ref{tab:victorybad}, {\em
218   cuts.  We have verified that this effect is due to the polarization of
219   the $W$ (we remove the polarization by reweighting the events and we get
220   good agreement between prediction and observation).  The kinematical
221 < requirements (lines 2 and 3) do not have a significant additional effect.
222 < Going from GEN to RECOSIM there is a significant change in observed/predicted.  
223 < We have tracked this down to the fact that tcMET underestimates the true \met
224 < by $\approx 4\%$\footnote{We find that observed/predicted changes by roughly 0.1
225 < for each 1.5\% change in \met response.}.  Finally, contamination from non $t\bar{t}$
226 < events can have a significant impact on the BG prediction.  The changes between
227 < lines 5 and 6 of Table~\ref{tab:victorybad} is driven by only {\color{red} 3}
228 < Drell Yan events that pass the \met selection.
221 > requirements (lines 2,3,4) compensate somewhat for the effect of W polarization.
222 > Going from GEN to RECOSIM, the change in observed/predicted is small.  
223 > % We have tracked this down to the fact that tcMET underestimates the true \met
224 > % by $\approx 4\%$\footnote{We find that observed/predicted changes by roughly 0.1
225 > %for each 1.5\% change in \met response.}.  
226 > Finally, contamination from non $t\bar{t}$
227 > events can have a significant impact on the BG prediction.  
228 > %The changes between
229 > %lines 6 and 7 of Table~\ref{tab:victorybad} is driven by 3
230 > %Drell Yan events that pass the \met selection in Monte Carlo (thus the effect
231 > %is statistically not well quantified).
232  
233   An additional source of concern is that the CMS Madgraph $t\bar{t}$ MC does
234   not include effects of spin correlations between the two top quarks.  
235   We have studied this effect at the generator level using Alpgen.  We find
236 < that the bias is a the few percent level.
236 > that the bias is at the few percent level.
237 >
238 > %%%TO BE REPLACED
239 > %Based on the results of Table~\ref{tab:victorybad}, we conclude that the
240 > %naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to
241 > %be corrected by a factor of {\color{red} $ K_{\rm{fudge}} =1.2 \pm 0.3$
242 > %(We still need to settle on thie exact value of this.
243 > %For the 11 pb analysis it is taken as =1.)} . The quoted
244 > %uncertainty is based on the stability of the Monte Carlo tests under
245 > %variations of event selections, choices of \met algorithm, etc.
246 > %For example, we find that observed/predicted changes by roughly 0.1
247 > %for each 1.5\% change in the average \met response.  
248  
249   Based on the results of Table~\ref{tab:victorybad}, we conclude that the
250 < naive data driven background estimate based on $P_T{\ell\ell)}$ needs to
251 < be corrected by a factor of {\color{red} $1.4 \pm 0.3$  (We need to
252 < decide what this number should be)}.  The quoted
253 < uncertainty is based on the stability of the Monte Carlo tests under
250 > naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to
251 > be corrected by a factor of $ K_C = X \pm Y$.
252 > The value of this correction factor as well as the systematic uncertainty
253 > will be assessed using 38X ttbar madgraph MC. In the following we use
254 > $K_C = 1$ for simplicity. Based on previous MC studies we foresee a correction
255 > factor of $K_C \approx 1.2 - 1.5$, and we will assess an uncertainty
256 > based on the stability of the Monte Carlo tests under
257   variations of event selections, choices of \met algorithm, etc.
258 + For example, we find that observed/predicted changes by roughly 0.1
259 + for each 1.5\% change in the average \met response.
260 +
261  
262  
263   \subsection{Signal Contamination}
264   \label{sec:sigcont}
265  
266 < All data-driven methods are principle subject to signal contaminations
266 > All data-driven methods are in principle subject to signal contaminations
267   in the control regions, and the methods described in
268   Sections~\ref{sec:abcd} and~\ref{sec:victory} are not exceptions.
269   Signal contamination tends to dilute the significance of a signal
# Line 191 | Line 276 | adds redundancy because signal contamina
276   in the different control regions for the two methods.
277   For example, in the extreme case of a
278   new physics signal
279 < with $P_T(\ell \ell) = \met$, an excess of ev ents would be seen
279 > with $P_T(\ell \ell) = \met$, an excess of events would be seen
280   in the ABCD method but not in the $P_T(\ell \ell)$ method.
281  
282 +
283   The LM points are benchmarks for SUSY analyses at CMS.  The effects
284   of signal contaminations for a couple such points are summarized
285 < in Table~\ref{tab:sigcontABCD} and~\ref{tab:sigcontPT}.
200 < Signal contamination is definitely an important
285 > in Table~\ref{tab:sigcont}. Signal contamination is definitely an important
286   effect for these two LM points, but it does not totally hide the
287   presence of the signal.
288  
289  
290   \begin{table}[htb]
291   \begin{center}
292 < \caption{\label{tab:sigcontABCD} Effects of signal contamination
293 < for the background predictions of the ABCD method including LM0 or
294 < LM1.  Results
295 < are normalized to 30 pb$^{-1}$.}
296 < \begin{tabular}{|c||c|c||c|c|}
212 < \hline
213 < SM         & LM0         & BG Prediction & LM1          & BG Prediction \\
214 < Background & Contribution& Including LM0 & Contribution & Including LM1  \\ \hline
215 < x          & x           & x             & x            & x \\
292 > \caption{\label{tab:sigcont} Effects of signal contamination
293 > for the two data-driven background estimates. The three columns give
294 > the expected yield in the signal region and the background estimates
295 > using the ABCD and $P_T(\ell \ell)$ methods. Results are normalized to 35~pb$^{-1}$.}
296 > \begin{tabular}{lccc}
297   \hline
298 < \end{tabular}
299 < \end{center}
300 < \end{table}
301 <
302 < \begin{table}[htb]
222 < \begin{center}
223 < \caption{\label{tab:sigcontPT} Effects of signal contamination
224 < for the background predictions of the $P_T(\ell\ell)$ method including LM0 or
225 < LM1.  Results
226 < are normalized to 30 pb$^{-1}$.}
227 < \begin{tabular}{|c||c|c||c|c|}
228 < \hline
229 < SM         & LM0         & BG Prediction & LM1          & BG Prediction \\
230 < Background & Contribution& Including LM0 & Contribution & Including LM1  \\ \hline
231 < x          & x           & x             & x            & x \\
298 >            &      Yield      &      ABCD    & $P_T(\ell \ell)$  \\
299 > \hline
300 > SM only     &      1.43       &      1.19    &             1.03  \\
301 > SM + LM0    &      7.90       &      4.23    &             2.35  \\
302 > SM + LM1    &      4.00       &      1.53    &             1.51  \\
303   \hline
304   \end{tabular}
305   \end{center}
306   \end{table}
307  
308 +
309 +
310 + %\begin{table}[htb]
311 + %\begin{center}
312 + %\caption{\label{tab:sigcontABCD} Effects of signal contamination
313 + %for the background predictions of the ABCD method including LM0 or
314 + %LM1.  Results
315 + %are normalized to 30 pb$^{-1}$.}
316 + %\begin{tabular}{|c|c||c|c||c|c|}
317 + %\hline
318 + %SM         & BG Prediction  & SM$+$LM0     & BG Prediction & SM$+$LM1     & BG Prediction \\
319 + %Background & SM Only        & Contribution & Including LM0 & Contribution & Including LM1  \\ \hline
320 + %1.2        & 1.0            & 6.8          & 3.7           & 3.4          & 1.3 \\
321 + %\hline
322 + %\end{tabular}
323 + %\end{center}
324 + %\end{table}
325 +
326 + %\begin{table}[htb]
327 + %\begin{center}
328 + %\caption{\label{tab:sigcontPT} Effects of signal contamination
329 + %for the background predictions of the $P_T(\ell\ell)$ method including LM0 or
330 + %LM1.  Results
331 + %are normalized to 30 pb$^{-1}$.}
332 + %\begin{tabular}{|c|c||c|c||c|c|}
333 + %\hline
334 + %SM         & BG Prediction  & SM$+$LM0     & BG Prediction & SM$+$LM1     & BG Prediction \\
335 + %Background & SM Only        & Contribution & Including LM0 & Contribution & Including LM1  \\ \hline
336 + %1.2        & 1.0            & 6.8          & 2.2           & 3.4          & 1.5 \\
337 + %\hline
338 + %\end{tabular}
339 + %\end{center}
340 + %\end{table}
341 +

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