| 10 |
|
process at NLO the NLO event generator MC@NLO 3.1~\cite{Frixione:2002ik} together with PDF set |
| 11 |
|
CTEQ6M was used. |
| 12 |
|
|
| 13 |
+ |
\subsection{Signal Definition} |
| 14 |
+ |
|
| 15 |
+ |
This analysis is studying the final state of on-shell $W$ and $Z$ |
| 16 |
+ |
boson, both of them decaying leptonically. The fully final leptonic |
| 17 |
+ |
final state $l^+ l^- l^\pm \nu$ also receives a contribution from the |
| 18 |
+ |
$W\gamma *$ process, where the $\gamma *$ stands for a virtual photon |
| 19 |
+ |
through the $WW\gamma$ vertex. In this analysis, only events with $l^+ |
| 20 |
+ |
l^-$ invariant mass consistent with $Z$ mass will be considered. CMS |
| 21 |
+ |
detector have a very good energy resolution for electrons and muons, |
| 22 |
+ |
the mass windows will be $\pm 10$ GeV around 91 GeV. |
| 23 |
+ |
|
| 24 |
+ |
Using MCFM to estimate the total NLO cross section, we found: |
| 25 |
+ |
\begin{equation} |
| 26 |
+ |
\sigma_{NLO} ( pp \rightarrow W^+Z^0; \sqrt{s}=14TeV) = 30.5 pb |
| 27 |
+ |
\end{equation} |
| 28 |
+ |
\begin{equation} |
| 29 |
+ |
\sigma_{NLO} ( pp \rightarrow W^-Z^0; \sqrt{s}=14TeV) = 19.1 pb |
| 30 |
+ |
\end{equation} |
| 31 |
+ |
|
| 32 |
+ |
The LO and NLO distribution of \Z transverse momentum are shown of |
| 33 |
+ |
figure~\ref{fig:LOvsNLO} for the case of $W^+$ on the left and $W^-$ |
| 34 |
+ |
on the right side. The ratio NLO/LO is also presented on the figure |
| 35 |
+ |
and it is increasing as $P_T(Z)$ increased. In the following analysis |
| 36 |
+ |
we consider a constant $k-factor$ of 1.84 as we concentrate on the |
| 37 |
+ |
first data taking. On the other side, if in the future one wants to |
| 38 |
+ |
use such distribution to study the effect of possible anomalous triple |
| 39 |
+ |
gauge couplings, it will be necessary to take the $p_T$ dependance of |
| 40 |
+ |
this $k-factor$ into account. |
| 41 |
+ |
|
| 42 |
+ |
\begin{figure}[!bt] |
| 43 |
+ |
\begin{center} |
| 44 |
+ |
\scalebox{0.8}{\includegraphics{figs/LOvsNLOZPtWminuns.eps}\includegraphics{figs/LOvsNLOZPtWplus.eps}} |
| 45 |
+ |
\caption{$P_T(Z)$ in $W^-Z$ events on the left and $W^+Z$ events on the right |
| 46 |
+ |
distribution for LO and NLO calculation. The ratio NLO/LO is also given. |
| 47 |
+ |
} |
| 48 |
+ |
\label{fig:LOvsNLO} |
| 49 |
+ |
\end{center} |
| 50 |
+ |
\end{figure} |
| 51 |
+ |
|
| 52 |
+ |
%# for bbll: |
| 53 |
+ |
%#CS NLO ((Z/gamma*->l+l-)bb) = 830pb = 345 pb * 2.4, where: |
| 54 |
+ |
%#- 345 pb is LO CS calculated with precision of ~0.15% |
| 55 |
+ |
%#- 2.4 is MCMF calculated k-factor with precision ~30% (!) |
| 56 |
+ |
%# 830x0.173 (== XS x eff.) = 143.59pb |
| 57 |
+ |
|
| 58 |
|
|
| 59 |
|
\subsection{Signal and Background Monte Carlo samples} |
| 60 |
|
|
| 61 |
+ |
\begin{table}[tbh] |
| 62 |
+ |
\begin{tabular}{llllll} \hline |
| 63 |
+ |
Sample & Generator & Sample name & Events & $\sigma \cdot \epsilon \cdot k$ & k-factor \\ \hline |
| 64 |
+ |
WZ & Pythia & /WZ/CMSSW\_1\_6\_7-CSA07-1195663763/RECO & 58897 & 0.585 pb & 1.92 \\ |
| 65 |
+ |
$Zb\bar{b}$ & COMPHEP & /comphep-bbll/CMSSW\_1\_6\_7-CSA07-1198677426/RECO & 143.59 pb & 2.4 \\ |
| 66 |
+ |
``Chowder'' & ALPGEN & /CSA07AllEvents/CMSSW\_1\_6\_7-CSA07-Chowder-A1-PDAllEvents-ReReco-100pb/RECO & 25 M & event weights & - \\ |
| 67 |
+ |
\hline |
| 68 |
+ |
\end{tabular} |
| 69 |
+ |
|
| 70 |
+ |
\caption{Monte Carlo samples used in this analysis} |
| 71 |
+ |
\end{table} |
| 72 |
+ |
|
| 73 |
|
|
| 74 |
|
|
| 75 |
|
|
