| 5 |
|
are generated with the leading order (LO) event generators |
| 6 |
|
{\sl PYTHIA}~\cite{Sjostrand:2003wg}, {\sl ALPGEN} and {\sl COMPHEP}. |
| 7 |
|
To accommodate the next-to-leading (NLO) effects, constant $k$-factors are applied |
| 8 |
< |
except for the signal where a $p_T$-dependence has been taken into account |
| 9 |
< |
and some of the backgrounds, $e.g.$ $t\bar{t}$, $W+jets$, and $Z+jets$ samples, |
| 10 |
< |
officially produced with NLO effects taken into account. |
| 8 |
> |
except for the signal where a $p_T$-dependence has been taken into account. |
| 9 |
|
|
| 10 |
|
The $p_T$-dependent $k$-factor for the signal is estimated using |
| 11 |
|
the NLO cross section calculator {\sl MCFM}~\cite{Campbell:2005}. |
| 12 |
|
We estimate the PDF uncertainty on the cross-section using |
| 13 |
< |
{\sl MC@NLO 3.1}~\cite{Frixione:2002ik} NLO event generator |
| 14 |
< |
together with CTEQ6M PDF set. |
| 13 |
> |
{\sl MC@NLO 3.1} NLO event generator~\cite{Frixione:2002ik} |
| 14 |
> |
together with CTEQ6M PDF set. |
| 15 |
|
|
| 16 |
|
\subsection{Signal definition} |
| 17 |
|
The goal of this analysis is to study the associative production of the on-shell |
| 28 |
|
\end{equation} |
| 29 |
|
|
| 30 |
|
The LO and NLO distributions of the \Z boson transverse momentum are |
| 31 |
< |
shown in Fig.~\ref{fig:LOvsNLO} with the case of $W^+$ on the left and $W^-$ |
| 34 |
< |
on the right side. The NLO/LO ratio, $k$-factor, is also presented on the figure, |
| 31 |
> |
shown in Fig.~\ref{fig:LOvsNLO}. The NLO/LO ratio, $k$-factor, is also presented on the figure, |
| 32 |
|
and it is increasing with $p_T(\Z)$. We take into account the $p_T$ dependence |
| 33 |
|
by re-weighting the LO Monte Carlo simulation as a function of the $p_T(\Z)$. |
| 34 |
|
% |
| 41 |
|
|
| 42 |
|
\begin{figure}[!bt] |
| 43 |
|
\begin{center} |
| 44 |
< |
\scalebox{0.8}{\includegraphics{figs/LOvsNLOZPtWminuns.eps}\includegraphics{figs/LOvsNLOZPtWplus.eps}} |
| 45 |
< |
\caption{$p_T(Z)$ distribution for LO (solid black histogram) and NLO (dashed black histogram) |
| 46 |
< |
in $W^-\Z$ events (left) and $W^+\Z$ events (right). The ratio NLO/LO is also given as a red |
| 47 |
< |
solid line. |
| 51 |
< |
} |
| 44 |
> |
\scalebox{0.8}{\includegraphics{figs/k_faktor_for_Note.eps}} |
| 45 |
> |
\caption{Top plot: comparison of $p_T(Z)$ distributions for NLO and LO for \WZ production |
| 46 |
> |
allowing off-shell vector bosons including photon contribution; |
| 47 |
> |
bottom plot: $k$-factor fit to a line.} |
| 48 |
|
\label{fig:LOvsNLO} |
| 49 |
|
\end{center} |
| 50 |
|
\end{figure} |
| 67 |
|
instrumental. The only physics background is from $Z^0Z^0$ production |
| 68 |
|
where one of the leptons is either mis-reconstructed or lost. |
| 69 |
|
|
| 70 |
< |
The instrumental backgrounds are all due to mis-identified electron candidates |
| 70 |
> |
The instrumental backgrounds are all due to misidentified electron candidates |
| 71 |
|
from either jets or photons. These backgrounds include production of $\W$ and $\Z$ bosons |
| 72 |
|
with jets and $t\bar{t}$ processes and $Z^0\gamma$ process. The background from $W\gamma$ |
| 73 |
< |
production, where the $\gamma$ converts and produces a dielectron system is neglected |
| 73 |
> |
production, where the $\gamma$ converts and produces a di-electron system is neglected |
| 74 |
|
due to a requirement on the $\ell^+\ell^-$ invariant mass to be consistent with the nominal \Z boson mass. |
| 75 |
|
|
| 76 |
|
All non-negligible instrumental backgrounds are summarized below. |
| 82 |
|
values of the jet transverse momentum. |
| 83 |
|
\item $t\bar{t}$: each of the top quarks decay into a $\W b$ pair producing at least two |
| 84 |
|
leptons and two $b$-quark jets. Although this process does not have a genuine $\Z$ |
| 85 |
< |
candidate and can be suppressed be a $\Z$ candidate invariant mass requirement, |
| 85 |
> |
candidate and can be suppressed by a $\Z$ candidate invariant mass requirement, |
| 86 |
|
the probability for a $b$-quark jet to decay semi-leptonically and be misidentified |
| 87 |
|
as a lepton is higher than that from a light-quark jets. The cross-section of the $t\bar{t}$ |
| 88 |
|
production is also exceed by about 15 times the cross-section of the \WZ production. |
| 100 |
|
generator. |
| 101 |
|
\item $Z^0\gamma$: this process is calculated with {\sl PYTHIA}. |
| 102 |
|
\end{itemize} |
| 103 |
+ |
The background sources that have \Z bosons described above are simulated with the |
| 104 |
+ |
contribution from the virtual photon. |
| 105 |
|
|
| 106 |
|
All the samples we use in this study are a part of the CSA07 production and |
| 107 |
|
are generated using $\mathrm{CMSSW}\_1\_4_\_6$ using the full {\sl GEANT} |
| 108 |
|
simulation of the CMS detector. The digitization and reconstruction are |
| 109 |
|
done using a newer $\mathrm{CMSSW}\_1\_6_\_7$ release with a |
| 110 |
< |
misalignment/miscalibration of the detector scenario expected |
| 110 |
> |
misalignment/mis-calibration of the detector scenario expected |
| 111 |
|
to be achieved after collection of $\sim$ 100~pb$^{-1}$ of data. |
| 112 |
|
All {\sl ALPGEN} samples are mixed together in further referred to as to a |
| 113 |
|
``Chowder soup''. |
| 136 |
|
Sample & cross section, pb & Events & Dataset name \\ \hline |
| 137 |
|
$\WZ$ & 1.12 & 59K & /WZ/CMSSW$\_1\_6\_7$-CSA07-1195663763\\ \hline |
| 138 |
|
$\Z b\bar{b}$ & 830*0.173 (NLO) & 1.9M & /comphep-bbll/CMSSW$\_1\_6\_7$-CSA07-1198677426\\ \hline |
| 139 |
< |
Chowder & Event Weight & $\sim$ 21M & /CSA07AllEvents/\\ & & & CMSSW$\_1\_6\_7$-CSA07-Chowder-A1-PDAllEvents-ReReco |
| 139 |
> |
Chowder & Event Weight & $\sim$ 25M & /CSA07AllEvents/\\ & & & CMSSW$\_1\_6\_7$-CSA07-Chowder-A1-PDAllEvents-ReReco |
| 140 |
|
-100pb\\ \hline |
| 141 |
< |
$\Z\Z$ inclusive & 16.1 (NLO) & $\sim$ 140k & /ZZ$\_$incl/CMSSW$\_1\_6\_7$-CSA07-1194964234/RECO\\ \hline |
| 142 |
< |
$\Z\gamma \rightarrow e^+e^-\gamma$ & 1.08 (NLO) & $\sim$125k &/Zeegamma/CMSSW$\_1\_6\_7$-CSA07-1198935518/RECO \\ \hline |
| 143 |
< |
$\Z\gamma \rightarrow \mu^+\mu^-\gamma$ & 1.08 (NLO) & $\sim$ 93k & /Zmumugamma/CMSSW$\_1\_6\_7$-CSA07-1194806860/RECO\\ \hline |
| 141 |
> |
$\Z\Z$ inclusive & 16.1 (NLO) & $\sim$ 140K & /ZZ$\_$incl/CMSSW$\_1\_6\_7$-CSA07-1194964234/RECO\\ \hline |
| 142 |
> |
$\Z\gamma \rightarrow e^+e^-\gamma$ & 1.08 (NLO) & $\sim$125K &/Zeegamma/CMSSW$\_1\_6\_7$-CSA07-1198935518/RECO \\ \hline |
| 143 |
> |
$\Z\gamma \rightarrow \mu^+\mu^-\gamma$ & 1.08 (NLO) & $\sim$ 93K & /Zmumugamma/CMSSW$\_1\_6\_7$-CSA07-1194806860/RECO\\ \hline |
| 144 |
|
\end{tabular} |
| 145 |
|
\label{tab:MC} |
| 146 |
|
\caption{Monte Carlo samples used in this analysis using 100 pb$^{-1}$ scenario} |
