| 23 |
|
|
| 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}. |
| 26 |
> |
as demonstrated in Fig.~\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 |
|
|
| 48 |
|
|
| 49 |
|
\begin{figure}[tb] |
| 50 |
|
\begin{center} |
| 51 |
< |
\includegraphics[width=0.5\linewidth, angle=90]{abcdMC.pdf} |
| 51 |
> |
\includegraphics[width=0.75\linewidth]{ttdil_uncor_38X.png} |
| 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.} |
| 53 |
> |
SumJetPt for SM Monte Carlo. Here we also show our choice of ABCD regions. The correlation coefficient |
| 54 |
> |
${\rm corr_{XY}}$ is computed for events falling in the ABCD regions.} |
| 55 |
|
\end{center} |
| 56 |
|
\end{figure} |
| 57 |
|
|
| 61 |
|
in the four regions for the SM Monte Carlo, as well as the background |
| 62 |
|
prediction A $\times$ C / B are given in Table~\ref{tab:abcdMC} for an integrated |
| 63 |
|
luminosity of 35 pb$^{-1}$. The ABCD method with chosen boundaries is accurate |
| 64 |
< |
to about 20\%, and we assess a corresponding systematic uncertainty. |
| 64 |
> |
to about 20\%, and we assess a corresponding systematic uncertainty |
| 65 |
> |
{\bf \color{red} More detail needed here???} |
| 66 |
|
|
| 67 |
|
%As shown in Table~\ref{tab:abcdsyst}, we assess systematic uncertainties |
| 68 |
|
%by varying the boundaries by an amount consistent with the hadronic energy scale uncertainty, |
| 146 |
|
|
| 147 |
|
\newcommand{\ptll} {\ensuremath{P_T(\ell\ell)}} |
| 148 |
|
\begin{center} |
| 149 |
< |
$ K = \frac{\int_0^{\infty} {\cal N}(\ptll)~~d\ptll~}{\int_{50}^{\infty} {\cal N}(\ptll)~~d\ptll~}$ |
| 149 |
> |
$ K = \frac{\int_0^{\infty} {\cal N}(\ptll)~~d\ptll~}{\int_{50}^{\infty} {\cal N}(\ptll)~~d\ptll~} = 1.52$ |
| 150 |
|
\end{center} |
| 151 |
|
|
| 152 |
|
|
| 151 |
– |
Monte Carlo studies give values of $K$ that are typically between 1.5 and 1.6, |
| 152 |
– |
depending on selection details. |
| 153 |
|
%%%TO BE REPLACED |
| 154 |
|
%Given the integrated luminosity of the |
| 155 |
|
%present dataset, the determination of $K$ in data is severely statistics |
| 234 |
|
up & 0.92 $ \pm $ 0.11 & 1.53 $ \pm $ 0.12 & 1.66 $ \pm $ 0.23 \\ |
| 235 |
|
down & 0.81 $ \pm $ 0.07 & 1.08 $ \pm $ 0.11 & 1.32 $ \pm $ 0.17 \\ |
| 236 |
|
\hline |
| 237 |
– |
|
| 238 |
– |
\hline |
| 237 |
|
MET smearing & Predicted & Observed & Obs/pred \\ |
| 238 |
|
\hline |
| 239 |
|
nominal & 0.92 $ \pm $ 0.11 & 1.29 $ \pm $ 0.11 & 1.40 $ \pm $ 0.20 \\ |
| 243 |
|
40\% & 0.85 $ \pm $ 0.07 & 1.37 $ \pm $ 0.11 & 1.61 $ \pm $ 0.19 \\ |
| 244 |
|
50\% & 1.08 $ \pm $ 0.18 & 1.36 $ \pm $ 0.11 & 1.26 $ \pm $ 0.24 \\ |
| 245 |
|
\hline |
| 248 |
– |
|
| 249 |
– |
\hline |
| 246 |
|
non-$t\bar{t} \to$~dilepton scale factor & Predicted & Observed & Obs/pred \\ |
| 247 |
|
\hline |
| 248 |
|
ttdil only & 0.77 $ \pm $ 0.07 & 1.05 $ \pm $ 0.06 & 1.36 $ \pm $ 0.14 \\ |
| 277 |
|
We have studied this effect at the generator level using Alpgen. We find |
| 278 |
|
that the bias is at the few percent level. |
| 279 |
|
|
| 280 |
< |
Based on the results of Table~\ref{tab:victorybad}, we conclude that the |
| 280 |
> |
Based on the results of Table~\ref{tab:victorysyst}, we conclude that the |
| 281 |
|
naive data-driven background estimate based on $P_T{(\ell\ell)}$ needs to |
| 282 |
< |
be corrected by a factor of $ K_C = 1.4 \pm 0.2(stat)$. |
| 282 |
> |
be corrected by a factor of $ K_C = 1.4 \pm 0.2({\rm stat})$. |
| 283 |
|
|
| 284 |
< |
The 2 dominant sources of systematic uncertainty in $K_C$ are due to non-$t\bar{t} \to$~dilepton backgrounds, |
| 285 |
< |
and the MET scale and resolution uncertainties. The impact of non-$t\bar{t}$-dilepton background is assessed |
| 286 |
< |
by varying the yield of all backgrounds except for $t\bar{t} \to$~dilepton, as shown in Table~\ref{table_kc}. |
| 287 |
< |
The systematic is assessed as the larger of the differences between the nominal $K_C$ value and the values |
| 284 |
> |
The dominant sources of systematic uncertainty in $K_C$ are due to non-$t\bar{t} \to$~dilepton backgrounds, |
| 285 |
> |
and the MET scale and resolution uncertainties, as summarized in Table~\ref{tab:victorysyst}. |
| 286 |
> |
The impact of non-$t\bar{t}$-dilepton background is assessed |
| 287 |
> |
by varying the yield of all backgrounds except for $t\bar{t} \to$~dilepton. |
| 288 |
> |
The uncertainty is assessed as the larger of the differences between the nominal $K_C$ value and the values |
| 289 |
|
obtained using only $t\bar{t} \to$~dilepton MC and obtained by doubling the non $t\bar{t} \to$~dilepton component, |
| 290 |
|
giving an uncertainty of $0.04$. |
| 291 |
|
|
| 292 |
|
The uncertainty in $K_C$ due to the MET scale uncertainty is assessed by varying the hadronic energy scale using |
| 293 |
< |
the same method as in~\ref{} and checking how much $K_C$ changes, as summarized in Table~\ref{tab:victorysyst}. |
| 294 |
< |
This gives an uncertainty of 0.3. We also assess the impact of the MET resolution uncertainty on $K_C$ by applying |
| 295 |
< |
a random smearing to the MET. For each event, we determine the expected MET resolution based on the sumJetPt, and |
| 296 |
< |
smear the MET to simulate an increase in the resolution of 10\%, 20\%, 30\%, 40\% and 50\%. The results show that |
| 300 |
< |
$K_C$ does not depend strongly on the MET resolution and we therefore do not assess any uncertainty. |
| 293 |
> |
the same method as in~\ref{ref:top}, giving an uncertainty of 0.3. We also assess the impact of the MET resolution |
| 294 |
> |
uncertainty on $K_C$ by applying a random smearing to the MET. For each event, we determine the expected MET resolution |
| 295 |
> |
based on the sumJetPt, and smear the MET to simulate an increase in the resolution of 10\%, 20\%, 30\%, 40\% and 50\%. |
| 296 |
> |
The results show that $K_C$ does not depend strongly on the MET resolution and we therefore do not assess any uncertainty. |
| 297 |
|
|
| 298 |
|
Incorporating all the statistical and systematic uncertainties we find $K_C = 1.4 \pm 0.4$. |
| 299 |
|
|
