
\vspace{0.2in}
{\bf Event Samples}\\ \nopagebreak

The event samples used in this SHW--based analysis were generated
simultaneously with the samples used in the $ZH\rightarrow\nn\bb$ SHW--based
analysis described previously.

\vspace{0.2in}
{\bf Event Selection} \\ \nopagebreak

$ZH \rightarrow l^{+} l^{-} b \bar{b}$ events are selected by the following
criteria:

\begin{itemize}
  \item 2 $b$-jets: 
  \begin{itemize} 
     \item[-] one tight $b$-tagged jet with $\et>20$ GeV and $|\eta|<2$ 
     \item[-] one loose $b$-tagged jet with $\et>15$ GeV and $|\eta|<2$ 
  \end{itemize} 
   \item at least two opposite sign leptons ($e$ or $\mu$) of the same flavor,
     \\ (tau's are not explicitly searched for, but they contribute to the 
      $\met$ analysis) 
   \item both leptons with $\pt>10$ GeV/c \item dilepton mass within 10 
       GeV/c$^2$ of the $Z$ mass 
   \item scalar sum of hadronic energy $H_T<175$ GeV
\end{itemize}

\begin{table}[h!]
  \caption{$ZH\rightarrow\lpm\bb$, SHW analysis.
           Expected number of $l^{+}l^{-}b\bar{b}$ signal and background events in 
           1~fb$^{-1}$ (per experiment) for various Higgs masses. Numbers in
           parentheses are for a 10\% $\bb$ mass resolution.}
  \label{ll_sig}
  \begin{tabular}{l|c|c|c|c|c}
\noalign{\vskip-8pt}
$m_H$ (GeV/$c^2$) & 90        & 100          & 110          & 120          & 130 \\
\tableline
$\Delta M$     & 70--110      & 80--125      & 85--130      & 90--140      & 95--150 \\ 
$\Delta M$     & (80--105)    & (90--120)    & (95--125)    & (105--135)   & (115--145) \\
\tableline
$ZH$ signal    & 1.5          & 1.2          & 0.9          & 0.6          & 0.4 \\
\hline
$ZZ$           & 2.2  (2.2)   & 2.1  (1.6)   & 1.9  (0.8)   & 1.5  (0.1)   & 1.2  (0.0)\\
$Zb\bar{b}$    & 2.9  (1.6)   & 2.4  (1.4)   & 2.1  (1.2)   & 2.0  (1.0)   & 1.9  (0.8)\\
$t\bar{t}$     & 1.8  (1.1)   & 1.9  (1.3)   & 1.8  (1.2)   & 1.9  (1.2)   & 1.9  (1.1)\\
background     & 6.9  (4.9)   & 6.4  (4.3)   & 5.8  (3.2)   & 5.4  (2.3)   & 5.0  (1.9) \\
\tableline
$S/\sqrt{B}$   & 0.57  (0.7) & 0.47  (0.6) & 0.37  (0.5) & 0.26  (0.4) & 0.18  (0.3) \\
  \end{tabular}
%  \caption{$ZH\rightarrow\lpm\bb$, SHW analysis.
%           Expected number of $l^{+}l^{-}b\bar{b}$ signal and background events in 
%           1~fb$^{-1}$ (per experiment) for various Higgs masses. Numbers in
%           parentheses are for a 10\% $\bb$ mass resolution.}
%  \label{ll_sig}
\end{table}


\vspace{0.2in}
{\bf Results and Conclusions} \\ \nopagebreak

The event flow through these cuts is similar to that in the $\nu
\bar{\nu}$ analysis, except that there are no backgrounds involving
the $W$ in this case. The two leptons in these events provide an easy,
high efficiency trigger. The number of signal and background events
expected in 1~fb$^{-1}$, assuming a 100\% efficient trigger is shown
in Table~\ref{ll_sig}. These events are independent of both the $ZH
\rightarrow \nu \bar{\nu} b\bar{b}$ and $WH \rightarrow l \nu
b\bar{b}$ samples.

Combining both the $ZH\rightarrow\nn\bb$ and $ZH\rightarrow\lpm\bb$
channels, a three sigma observation of a 100 GeV/$c^2$ Higgs would
require 8~fb$^{-1}$ for a single experiment.  If a 30\% improvement in
mass resolution with respect to that of Run~1 can be achieved, only
5~fb$^{-1}$ would be required.  The mass distribution for both signal
and background in 10~fb$^{-1}$ is shown in fig.~\ref{ZH_mass}.

%\begin{table}
%  \begin{tabular}{l|c|c|c|c|c}
%$m_H$ (GeV/$c^2$)             & 90           & 100          & 110          & 120          & 130 \\
%\hline
%$Z(W)H \rightarrow \met b\bar{b}$  & 8.9          & 6.7          & 4.6          & 3.2          & 2.1 \\
%$ZH \rightarrow l^{+}l^{-} b \bar{b}$          & 1.5          & 1.2          & 0.9          & 0.6          & 0.4 \\
%Signal                     & 10.4         & 7.9          & 5.5          & 3.8          & 2.5 \\
%\hline
%$\met b\bar{b}$ background            & 51.1  (32.3) & 47.2  (28.9) & 42.8  (22.0) & 40.7  (15.1) & 37.0  (11.7) \\
%$l^{+}l^{-} b \bar{b}$ background    &  6.9   (4.5) &  6.4   (3.9) &  5.8   (2.8) &  5.4  ( 2.1) &  5.0   (1.7) \\
%Background                 & 58.0  (36.8) & 53.6  (32.8) & 48.6  (24.8) & 46.1  (17.2) & 42.0  (13.4) \\
%\hline
%$S/\sqrt{B}$               & 1.37  (1.71) & 1.08  (1.37) & 0.79  (1.10) & 0.56  (0.92) & 0.39  (0.68) \\
%  \end{tabular}
%  \caption{$ZH\rightarrow\nn\bb$ and $ZH\rightarrow\lpm\bb$, SHW analysis.
%           Expected number of combined signal and background events in 1 fb$^{-1}$
%           (per single experiment) for various Higgs masses. Numbers in parentheses are
%           for a factor of two improvement in mass resolution.}
%  \label{ZH_sig}
%\end{table}


\begin{figure}
  \begin{center}
    \parbox{4.0in}{\epsfxsize=\hsize\epsffile{zhll/mass_100_10fb_2xres.eps}}
  \end{center}
  \caption{Combined $ZH\to\nn\bb,\lpm\bb$ channels, using the SHW analysis.  
      The plot shows the $b\bar{b}$ dijet mass distribution for a 100 GeV/$c^2$ 
      Higgs and background in 10 fb$^{-1}$.}
  \label{ZH_mass}
\end{figure}

