ViewVC Help
View File | Revision Log | Show Annotations | Root Listing
root/cvsroot/UserCode/claudioc/OSNote2010/datadriven.tex
(Generate patch)

Comparing UserCode/claudioc/OSNote2010/datadriven.tex (file contents):
Revision 1.4 by claudioc, Mon Nov 1 17:52:52 2010 UTC vs.
Revision 1.25 by benhoob, Sat Nov 20 15:26:05 2010 UTC

# 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 >              sample   &                   A   &                   B   &                   C   &                   D   &                PRED  \\
90 > \hline
91 > $t\bar{t}\rightarrow \ell^{+}\ell^{-}$         &   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  \\
92 > $Z^0 \rightarrow \ell^{+}\ell^{-}$             &   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  \\
93 >            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  \\
94 > \hline
95 >         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  \\
96 > \hline
97 > \end{tabular}
98 > \end{center}
99 > \end{table}
100 >
101 >
102 >
103 > \begin{table}[ht]
104 > \begin{center}
105 > \caption{\label{tab:abcdsyst} Results of the systematic study of the ABCD method by varying the boundaries
106 > between the ABCD regions shown in Fig.~\ref{fig:abcdMC}. Here $x_1$ is the lower SumJetPt boundary and
107 > $x_2$ is the boundary separating regions A and B from C and D, their nominal values are 125 and 300~GeV,
108 > respectively. $y_1$ is the lower MET/$\sqrt{\rm SumJetPt}$ boundary and
109 > $y_2$ is the boundary separating regions B and C from A and D, their nominal values are 4.5 and 8.5~GeV$^{1/2}$,
110 > respectively.}
111 > \begin{tabular}{cccc|c}
112 > \hline
113 > $x_1$   &   $x_2$ & $y_1$   &   $y_2$ & Observed/Predicted \\
114 > \hline
115 > nominal & nominal & nominal & nominal & 1.20     \\
116 > +5\%    & +5\%    & +2.5\%  & +2.5\%  & 1.38     \\
117 > +5\%    & +5\%    & nominal & nominal & 1.31     \\
118 > nominal & nominal & +2.5\%  & +2.5\%  & 1.25     \\
119 > nominal & +5\%    & nominal & +2.5\%  & 1.32     \\
120 > nominal & -5\%    & nominal & -2.5\%  & 1.16     \\
121 > -5\%    & -5\%    & +2.5\%  & +2.5\%  & 1.21     \\
122 > +5\%    & +5\%    & -2.5\%  & -2.5\%  & 1.26     \\
123   \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
124   \end{tabular}
125   \end{center}
126   \end{table}
# Line 89 | Line 141 | In practice one has to rescale the resul
141   to account for the fact that any dilepton selection must include a
142   moderate \met cut in order to reduce Drell Yan backgrounds.  This
143   is discussed in Section 5.3 of Reference~\cite{ref:ourvictory}; for a \met
144 < cut of 50 GeV, the rescaling factor is obtained from the data as
144 > cut of 50 GeV, the rescaling factor is obtained from the MC as
145  
146   \newcommand{\ptll} {\ensuremath{P_T(\ell\ell)}}
147   \begin{center}
# Line 98 | Line 150 | $ K = \frac{\int_0^{\infty} {\cal N}(\pt
150  
151  
152   Monte Carlo studies give values of $K$ that are typically between 1.5 and 1.6,
153 < depending on selection details.
153 > depending on selection details.  
154 > %%%TO BE REPLACED
155 > %Given the integrated luminosity of the
156 > %present dataset, the determination of $K$ in data is severely statistics
157 > %limited.  Thus, we take $K$ from $t\bar{t}$ Monte Carlo as
158 >
159 > %\begin{center}
160 > %$ K_{MC} = \frac{\int_0^{\infty} {\cal N}(\met)~~d\met~}{\int_{50}^{\infty} {\cal N}(\met)~~d\met~}$
161 > %\end{center}
162 >
163 > %\noindent {\color{red} For the 11 pb result we have used $K$ from data.}
164  
165   There are several effects that spoil the correspondance between \met and
166   $P_T(\ell\ell)$:
167   \begin{itemize}
168   \item $Ws$ in top events are polarized.  Neutrinos are emitted preferentially
169 < forward in the $W$ rest frame, thus the $P_T(\nu\nu)$ distribution is harder
169 > parallel to the $W$ velocity while charged leptons are emitted prefertially
170 > anti-parallel. Thus the $P_T(\nu\nu)$ distribution is harder
171   than the $P_T(\ell\ell)$ distribution for top dilepton events.
172   \item The lepton selections results in $P_T$ and $\eta$ cuts on the individual
173   leptons that have no simple correspondance to the neutrino requirements.
174   \item Similarly, the \met$>$50 GeV cut introduces an asymmetry between leptons and
175   neutrinos which is only partially compensated by the $K$ factor above.
176   \item The \met resolution is much worse than the dilepton $P_T$ resolution.
177 < When convoluted with a falling spectrum in the tails of \met, this result
177 > When convoluted with a falling spectrum in the tails of \met, this results
178   in a harder spectrum for \met than the original $P_T(\nu\nu)$.
179   \item The \met response in CMS is not exactly 1.  This causes a distortion
180   in the \met distribution that is not present in the $P_T(\ell\ell)$ distribution.
# Line 122 | Line 185 | of $P_T(\ell\ell)$ and $P_T(\nu\nu)$ do
185   sources.  These events can affect the background prediction.  Particularly
186   dangerous are high $P_T$ Drell Yan events that barely pass the \met$>$ 50
187   GeV selection.  They will tend to push the data-driven background prediction up.
188 + Therefore we estimate the number of DY events entering the background prediction
189 + using the $R_{out/in}$ method as described in Sec.~\ref{sec:othBG}.
190   \end{itemize}
191  
192   We have studied these effects in SM Monte Carlo, using a mixture of generator and
# Line 134 | Line 199 | The results are summarized in Table~\ref
199   \begin{center}
200   \caption{\label{tab:victorybad} Test of the data driven method in Monte Carlo
201   under different assumptions.  See text for details.}
202 < \begin{tabular}{|l|c|c|c|c|c|c|c|}
202 > \begin{tabular}{|l|c|c|c|c|c|c|c|c|}
203   \hline
204 < & True $t\bar{t}$ dilepton & $t\to W\to\tau$& other SM & GEN or  & Lepton $P_T$    & \met $>$ 50& obs/pred \\
205 < & included                 & included  & included & RECOSIM & and $\eta$ cuts &      &     \\ \hline
206 < 1&Y                        &     N     &   N      &  GEN    &   N             &   N  &       \\
207 < 2&Y                        &     N     &   N      &  GEN    &   Y             &   N  &   \\
208 < 3&Y                        &     N     &   N      &  GEN    &   Y             &   Y  &   \\
209 < 4&Y                        &     N     &   N      & RECOSIM &   Y             &   Y  &   \\
210 < 5&Y                        &     Y     &   N      & RECOSIM &   Y             &   Y  &   \\
211 < 6&Y                        &     Y     &   Y      & RECOSIM &   Y             &   Y  &   \\
204 > & True $t\bar{t}$ dilepton & $t\to W\to\tau$& other SM & GEN or  & Lepton $P_T$    & Z veto & \met $>$ 50& obs/pred \\
205 > & included                 & included       & included & RECOSIM & and $\eta$ cuts &        &            &  \\ \hline
206 > 1&Y                        &     N          &   N      &  GEN    &   N             &   N    & N          & 1.90  \\
207 > 2&Y                        &     N          &   N      &  GEN    &   Y             &   N    & N          & 1.64  \\
208 > 3&Y                        &     N          &   N      &  GEN    &   Y             &   Y    & N          & 1.59  \\
209 > 4&Y                        &     N          &   N      &  GEN    &   Y             &   Y    & Y          & 1.55  \\
210 > 5&Y                        &     N          &   N      & RECOSIM &   Y             &   Y    & Y          & 1.51  \\
211 > 6&Y                        &     Y          &   N      & RECOSIM &   Y             &   Y    & Y          & 1.58  \\
212 > 7&Y                        &     Y          &   Y      & RECOSIM &   Y             &   Y    & Y          & 1.38  \\
213 > %%%NOTE: updated value 1.18 -> 1.46 since 2/3 DY events have been removed by updated analysis selections,
214 > %%%dpt/pt cut and general lepton veto
215   \hline
216   \end{tabular}
217   \end{center}
# Line 155 | Line 223 | line of Table~\ref{tab:victorybad}, {\em
223   cuts.  We have verified that this effect is due to the polarization of
224   the $W$ (we remove the polarization by reweighting the events and we get
225   good agreement between prediction and observation).  The kinematical
226 < requirements (lines 2 and 3) do not have a significant additional effect.
227 < Going from GEN to RECOSIM there is a significant change in observed/predicted.  
228 < We have tracked this down to the fact that tcMET underestimates the true \met
229 < by $\approx 4\%$\footnote{We find that observed/predicted changes by roughly 0.1
230 < for each 1.5\% change in \met response.}.  Finally, contamination from non $t\bar{t}$
231 < events can have a significant impact on the BG prediction.  The changes between
232 < lines 5 and 6 of Table~\ref{tab:victorybad} is driven by only {\color{red} 3}
233 < Drell Yan events that pass the \met selection.
226 > requirements (lines 2,3,4) compensate somewhat for the effect of W polarization.
227 > Going from GEN to RECOSIM, the change in observed/predicted is small.  
228 > % We have tracked this down to the fact that tcMET underestimates the true \met
229 > % by $\approx 4\%$\footnote{We find that observed/predicted changes by roughly 0.1
230 > %for each 1.5\% change in \met response.}.  
231 > Finally, contamination from non $t\bar{t}$
232 > events can have a significant impact on the BG prediction.  
233 > %The changes between
234 > %lines 6 and 7 of Table~\ref{tab:victorybad} is driven by 3
235 > %Drell Yan events that pass the \met selection in Monte Carlo (thus the effect
236 > %is statistically not well quantified).
237  
238   An additional source of concern is that the CMS Madgraph $t\bar{t}$ MC does
239   not include effects of spin correlations between the two top quarks.  
240   We have studied this effect at the generator level using Alpgen.  We find
241 < that the bias is a the few percent level.
241 > that the bias is at the few percent level.
242 >
243 > %%%TO BE REPLACED
244 > %Based on the results of Table~\ref{tab:victorybad}, we conclude that the
245 > %naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to
246 > %be corrected by a factor of {\color{red} $ K_{\rm{fudge}} =1.2 \pm 0.3$
247 > %(We still need to settle on thie exact value of this.
248 > %For the 11 pb analysis it is taken as =1.)} . The quoted
249 > %uncertainty is based on the stability of the Monte Carlo tests under
250 > %variations of event selections, choices of \met algorithm, etc.
251 > %For example, we find that observed/predicted changes by roughly 0.1
252 > %for each 1.5\% change in the average \met response.  
253  
254   Based on the results of Table~\ref{tab:victorybad}, we conclude that the
255 < naive data driven background estimate based on $P_T{\ell\ell)}$ needs to
256 < be corrected by a factor of {\color{red} $1.4 \pm 0.3$  (We need to
257 < decide what this number should be)}.  The quoted
258 < uncertainty is based on the stability of the Monte Carlo tests under
255 > naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to
256 > be corrected by a factor of $ K_C = X \pm Y$.
257 > The value of this correction factor as well as the systematic uncertainty
258 > will be assessed using 38X ttbar madgraph MC. In the following we use
259 > $K_C = 1$ for simplicity. Based on previous MC studies we foresee a correction
260 > factor of $K_C \approx 1.2 - 1.5$, and we will assess an uncertainty
261 > based on the stability of the Monte Carlo tests under
262   variations of event selections, choices of \met algorithm, etc.
263 + For example, we find that observed/predicted changes by roughly 0.1
264 + for each 1.5\% change in the average \met response.
265 +
266  
267  
268   \subsection{Signal Contamination}
269   \label{sec:sigcont}
270  
271 < All data-driven methods are principle subject to signal contaminations
271 > All data-driven methods are in principle subject to signal contaminations
272   in the control regions, and the methods described in
273   Sections~\ref{sec:abcd} and~\ref{sec:victory} are not exceptions.
274   Signal contamination tends to dilute the significance of a signal
# Line 193 | Line 281 | adds redundancy because signal contamina
281   in the different control regions for the two methods.
282   For example, in the extreme case of a
283   new physics signal
284 < with $P_T(\ell \ell) = \met$, an excess of ev ents would be seen
284 > with $P_T(\ell \ell) = \met$, an excess of events would be seen
285   in the ABCD method but not in the $P_T(\ell \ell)$ method.
286  
287  
288   The LM points are benchmarks for SUSY analyses at CMS.  The effects
289   of signal contaminations for a couple such points are summarized
290 < in Table~\ref{tab:sigcontABCD} and~\ref{tab:sigcontPT}.
203 < Signal contamination is definitely an important
290 > in Table~\ref{tab:sigcont}. Signal contamination is definitely an important
291   effect for these two LM points, but it does not totally hide the
292   presence of the signal.
293  
294  
295   \begin{table}[htb]
296   \begin{center}
297 < \caption{\label{tab:sigcontABCD} Effects of signal contamination
298 < for the background predictions of the ABCD method including LM0 or
299 < LM1.  Results
300 < are normalized to 30 pb$^{-1}$.}
301 < \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 \\
297 > \caption{\label{tab:sigcont} Effects of signal contamination
298 > for the two data-driven background estimates. The three columns give
299 > the expected yield in the signal region and the background estimates
300 > using the ABCD and $P_T(\ell \ell)$ methods. Results are normalized to 35~pb$^{-1}$.}
301 > \begin{tabular}{lccc}
302   \hline
303 < \end{tabular}
304 < \end{center}
305 < \end{table}
306 <
307 < \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 \\
303 >            &      Yield      &      ABCD    & $P_T(\ell \ell)$  \\
304 > \hline
305 > SM only     &      1.43       &      1.19    &             1.03  \\
306 > SM + LM0    &      7.90       &      4.23    &             2.35  \\
307 > SM + LM1    &      4.00       &      1.53    &             1.51  \\
308   \hline
309   \end{tabular}
310   \end{center}
311   \end{table}
312  
313 +
314 +
315 + %\begin{table}[htb]
316 + %\begin{center}
317 + %\caption{\label{tab:sigcontABCD} Effects of signal contamination
318 + %for the background predictions of the ABCD method including LM0 or
319 + %LM1.  Results
320 + %are normalized to 30 pb$^{-1}$.}
321 + %\begin{tabular}{|c|c||c|c||c|c|}
322 + %\hline
323 + %SM         & BG Prediction  & SM$+$LM0     & BG Prediction & SM$+$LM1     & BG Prediction \\
324 + %Background & SM Only        & Contribution & Including LM0 & Contribution & Including LM1  \\ \hline
325 + %1.2        & 1.0            & 6.8          & 3.7           & 3.4          & 1.3 \\
326 + %\hline
327 + %\end{tabular}
328 + %\end{center}
329 + %\end{table}
330 +
331 + %\begin{table}[htb]
332 + %\begin{center}
333 + %\caption{\label{tab:sigcontPT} Effects of signal contamination
334 + %for the background predictions of the $P_T(\ell\ell)$ method including LM0 or
335 + %LM1.  Results
336 + %are normalized to 30 pb$^{-1}$.}
337 + %\begin{tabular}{|c|c||c|c||c|c|}
338 + %\hline
339 + %SM         & BG Prediction  & SM$+$LM0     & BG Prediction & SM$+$LM1     & BG Prediction \\
340 + %Background & SM Only        & Contribution & Including LM0 & Contribution & Including LM1  \\ \hline
341 + %1.2        & 1.0            & 6.8          & 2.2           & 3.4          & 1.5 \\
342 + %\hline
343 + %\end{tabular}
344 + %\end{center}
345 + %\end{table}
346 +

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines