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\begin{document}


\Title{Search for new physics with a Z boson, jets, and $\rm \bf E_{T}^{miss}$ at CMS (arXiv:1204.3774)}

\bigskip\bigskip

%+\addtocontents{toc}{{\it W. Andrews}}
%+\label{AndrewsStart}

\begin{raggedright}  

{\it Warren Andrews\index{Andrews, W.}\\
Department of Physics\\
University of California, San Diego\\
9500 Gilman Drive
La Jolla, CA 92093, USA}
\bigskip\bigskip
\end{raggedright}


\section{Introduction}

We search for physics beyond the standard model in events containing a leptonically decaying Z boson (Z $\rightarrow\ell^+\ell^-$, $\ell=e,\mu$), jets, and missing transverse energy ($\rm E_{T}^{miss}$). The search is performed using 4.98 fb$^{-1}$ of $\sqrt{s}$ = 7 TeV data collected by the CMS experiment at the LHC in 2011.    
\cite{Chatrchyan:2012qka}

After selecting Z $\rightarrow\ell^+\ell^-$ ($\ell=e,\mu$), the main backgrounds include Z plus jets where the $\rm E_{T}^{miss}$ comes from jet mismeasurement, dileptonic $t\bar{t}$ where the dileptons happen to fall in the Z mass window, and diboson processes.

The Z plus jets background is predicted using the $\rm E_{T}^{miss}$ templates method, flavor symmetric backgrounds (such as $t\bar{t}$) are predicted from opposite flavor ($e\mu$) events, and the diboson background (VZ) is taken from MC simulation.


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%\includegraphics[width=0.49\linewidth]{images/hdilmass_mm_allj.pdf}
%\caption{Dilepton mass distribution in ee (left) and $\mu\mu$ (right) channels.}
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\section{$\rm E_{T}^{miss}$ Templates Method}
\index{$\rm E_{T}^{miss}$ Templates Method}

This data-driven technique uses $\gamma$ plus jets events as a control sample to predict the $\rm E_{T}^{miss}$ in Z plus jets, and is predicated on the fact that fake $\rm E_{T}^{miss}$ from jet mismeasurement can be parameterized in terms of the $N_{\rm{jets}}$ and scalar sum of jet $p_T$ ($H_T$).
%
The $\rm E_{T}^{miss}$ templates are $\rm E_{T}^{miss}$ plots in $\gamma$ plus jets 
events binned in $N_{\rm{jets}}$ and $H_T$, normalized to unity.
The prediction of the $\rm E_{T}^{miss}$ distribution in Z plus jets is formed by summing the templates which correspond to the $N_{\rm{jets}}$ and $H_T$ in each Z plus jets event.

%The advantage of using $\gamma$ plus jets events to predict Z plus jets 
%events is that in both cases, 
%the hadronic system recoils against the boson.
%QCD events can also be used after correcting for the hadronic recoil effect.


%\section{Opposite Flavor Background Prediction}
%\index{Opposite Flavor Background Prediction}

%Backgrounds such as $t\bar{t}$ (dominant), single top (tW), WW, and Z $\rightarrow \tau\tau$
%are flavor symmetric in that opposite flavor (OF) and same flavor leptons appear at equal rates.
%Flavor symmetric backgrounds have equal rates of opposite flavor (OF) and same flavor leptons.
%Flavor symmetric backgrounds have equal rates of opposite flavor (OF) and same flavor leptons:
%$N(e\mu) = N(ee) + N(\mu\mu)$.
%We can therefore use OF data as a control sample to predict
%the contribution of these backgrounds to our same flavor signal regions.
%These Backgrounds include $t\bar{t}$ (dominant), single top (tW), WW, and Z $\rightarrow \tau\tau$.
%
%In order to decrease the statistical uncertainty on the prediction,
%we remove the dilepton mass cut and scale the yield by
%the ratio of events inside the Z mass window to the total
%(taken from MC). The value of this ratio is 0.16 $\pm$ 0.01.
%
%The difference in identification efficiency between electrons and muons is
%accounted for by scaling the OF yield by the ratio of these efficiencies, 
%$R_{\mu e}=1.07 \pm 0.07$ where the uncertainty is due to %in this quantity is based on% the small
%variation with respect to lepton $p_T$.


\section{Results}
\index{Results}

The signal regions are formed by applying $\rm E_{T}^{miss}$ cuts as shown in the table, and
most expected sensitivity comes from $\rm E_{T}^{miss}$ $>$ 100, 200, and 
300 GeV. Lower $\rm E_{T}^{miss}$ cuts are shown as a validation of the background predictions.
The results shown here are for $N_{\rm{jets}}$ $\ge 2$; see the paper (arXiv:1204.3774)
for $N_{\rm{jets}}$ $\ge 3$ results.

The background estimations described above are compared with observed yields
and used to derive model independent upper limits (UL) on new physics contributions.
Uncertainties include both statistical and systematic contributions.
For the observed yield (data), the first (second) number in parentheses is the 
yield in the $ee$ ($\mu\mu$) final state.
Background predictions agree with data: no evidence for new physics.

We show yields for two example cMSSM model points (LM4 and LM8), both of which
are ruled out.


\begin{figure}[htb]
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\includegraphics[width=0.4\linewidth]{metplot_2jets.pdf}

\caption{Data and background predictions as a function of $\rm E_{T}^{miss}$.}
\label{fig:results}
\end{center}
\end{figure}


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\begin{table}[b]
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{\scriptsize %footnotesize %\
\begin{tabular}{l|ccccc}
\hline
\hline
              &   $N_{\rm{jets}}$ $>30$ GeV   & $N_{\rm{jets}}$ $>60$  GeV   & $N_{\rm{jets}}$ $>100$ GeV   &   $N_{\rm{jets}}$ $>200$ GeV  &  $N_{\rm{jets}}$ $>$ 300 GeV \\
\hline		  
Z bkg       &   15070 $\pm$ 4825  &    484 $\pm$  156  &     36 $\pm$   12  &     2.4 $\pm$    0.9  &    0.4 $\pm$  0.3 \\
OF bkg        &    1116 $\pm$  101  &    680 $\pm$   62  &    227 $\pm$   21  &      11 $\pm$    3.2  &    1.6 $\pm$  0.6 \\
VZ bkg        &     269 $\pm$  135  &     84 $\pm$   42  &     35 $\pm$   17  &     5.3 $\pm$    2.7  &    1.2 $\pm$  0.7 \\
\hline
\hline
Total bkg     &    16455 $\pm$ 4828 &    1249 $\pm$  174 &    297 $\pm$   30  &     19 $\pm$     4.3  &    3.2 $\pm$  1.0 \\
Data          &    16483 (8243,8240)&    1169 (615,554)  &    290 (142,148)   &     14 (8,6)          &    0 \\
\hline
\hline
Observed UL           & 9504           &  300           &   57            &     8.3          &   3.0         \\
Expected UL           & 9478           &  349           &   60            &      11          &   4.6         \\
LM4                   & $120 \pm 7.0$  &  $108 \pm 6.7$  &  $93 \pm 6.6$  &  $53 \pm 7.3$  &  $24 \pm 6.2$   \\
LM8                   &  $52 \pm 3.2$  &   $46 \pm 3.0$  &  $37 \pm 2.8$  &  $21 \pm 2.8$  &  $9.1 \pm 2.3$  \\
\hline
\hline
\end{tabular}
}

\label{tab:results}
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%\section{Interpretation}
%\index{Interpretation}
%
%Final states with Z bosons are predicted in many models of BSM physics, such as supersymmetry (SUSY). 
%For example, the production of a Z boson in the decay $\tilde{\chi}_2^0$ $\rightarrow$ $\tilde{\chi}_1^0$Z, 
%%where \chioz\ (\chitz) is the lightest (second lightest) neutralino,
%where $\tilde{\chi}^0$ are neutralinos,
%is a direct consequence of the gauge structure of SUSY, and can become a favored  channel
%in SUSY parameter space where the neutralinos have a large Higgsino or neutral Wino component.
%
%We interpret our results in the context of simplified model scans (SMS) which represent 
%decay chains of possible new particles.
%The diagram shown contains a gluino which decays to two quarks and a heavy neutralino ($\tilde{\chi}_2^0$);
%the $\tilde{\chi}_2^0$ then decays to a Z and the LSP ($\tilde{\chi}_1^0$), which is only seen as $\rm E_{T}^{miss}$.
%
%We provide efficiencies for each scan point which may be used to validate efficiency models
%and then applied to other new physics scenarios. We also provide cross section ULs, as shown.
%
%\begin{center}
%%\vspace{-0.9cm}
%\includegraphics[width=0.4\linewidth]{images/T5zz.pdf}
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%%\vspace{-0.2cm}
%\includegraphics[trim=10cm 0.2cm 0cm 0.4cm,clip,width=0.4\linewidth]{images/SMS_T5zz_2jets.pdf}
%\end{center}


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%\cite{Chatrchyan:2012qka}
\bibitem{Chatrchyan:2012qka} 
  S.~Chatrchyan {\it et al.}  [CMS Collaboration],
  %``Search for physics beyond the standard model in events with a Z boson, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV,''
  arXiv:1204.3774 [hep-ex].
  %%CITATION = ARXIV:1204.3774;%%


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