\vspace{0.1in}
\small
\begin{center}
{\it Tao Han,
     A. Lucotte,
     M. Schmitt,
     A.S Turcot,
     R.-J. Zhang
     }
\end{center}
\normalsize \nopagebreak

%my defs:
\def\mh{m_h^{}}
\def\gev{\rm GeV}
\def\fbi{\rm fb^{-1}}
\def\ww{W^*W^*}
\def\zz{Z^*Z^*}
\def\lsim{\mathrel{\raise.3ex\hbox{$<$\kern-.75em\lower1ex\hbox{$\sim$}}}}
\def\gsim{\mathrel{\raise.3ex\hbox{$>$\kern-.75em\lower1ex\hbox{$\sim$}}}}
\def\ljj{\ell\nu jj}
\def\lljj{\ell\bar\ell jj}
\def\jj{\protect jj}
\def\llnn{\ell\bar\ell\nu\bar\nu}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%  Slash character...

\newcommand{ \slashchar }[1]{\setbox0=\hbox{$#1$}   % set a box for #1
   \dimen0=\wd0                                     % and get its size
   \setbox1=\hbox{/} \dimen1=\wd1                   % get size of /
   \ifdim\dimen0>\dimen1                            % #1 is bigger
      \rlap{\hbox to \dimen0{\hfil/\hfil}}          % so center / in box
      #1                                            % and print #1
   \else                                            % / is bigger
      \rlap{\hbox to \dimen1{\hfil$#1$\hfil}}       % so center #1
      /                                             % and print /
   \fi}                                             %

%%EXAMPLE:  $\slashchar{E}$ or $\slashchar{E}_{t}$
\def\ptmiss{\slashchar{p}_{T}}
\def\etmiss{\slashchar{E}_{T}}


\input{epsf}
\ifx\epsffile\undefined
\message{(Uncomment input epsf to include figures)}
\newlength{\epsfysize}
\def\epsffile#1#2#3#4]#5{}
\fi

As previous studies and the present studies have
shown, in the Higgs mass region where the $\bb$ decay mode dominates
the most sensitive channels are those arising from the associated 
production of an electroweak gauge boson and the (SM, or SM-like) 
Higgs boson $h$~\cite{Stange:1994ya,GH,steve}:
\begin{equation}
   p\bar p \to W hX,\ ZhX.
  \label{whzh}
\end{equation}
However, as shown in the first section of this report the leading
production mechanism for a SM-like Higgs boson at the Tevatron is the
gluon-fusion process via heavy quark triangle loops
\begin{equation}
  p \bar p \to gg X\to h X.
  \label{gluon}
\end{equation}

There are also contributions to $h$ production from the vector boson
fusion processes\footnote{Here and henceforth, $W^*(Z^*)$ generically
denotes a $W(Z)$ boson of either on- or off-mass-shell.}
\begin{equation}
  \ww,\ \zz \to h,
  \label{wwzz}
\end{equation}
where $\ww$ and $\zz$ are radiated from the quark partons.  In
Fig.~\ref{fg:4}, we present cross sections for SM Higgs boson
production at the Tevatron for processes (\ref{whzh}), (\ref{gluon})
and (\ref{wwzz}). We see that the gluon fusion process yields the
largest cross section, typically a factor of four above the associated
production (\ref{whzh}). For $\mh>160$ GeV, $WW,ZZ$ fusion processes
become comparable to that of (\ref{whzh}). In calculating the total
cross sections, the QCD corrections have been included for all the
processes~\cite{19,23,32}, and we have used the CTEQ4M
parton distribution functions~\cite{CTEQ}.

\begin{figure}[tbp]
  \begin{center}
    \parbox{5.5in}{\epsfxsize=\hsize\epsffile{highmass/sigxbr.eps}}
  \end{center}
  \caption[]{Standard Model Higgs boson production cross sections
             (in fb) and various subsequent decay modes versus $m_h$ for
             (a) $gg\to h \to W^*W^*$ (solid curves) and $Z^*Z^*$ (dashed
             curves). (b) $q \bar{q}' \to Wh$ with $h \to W^*W^*$ (solid
             curves) and $Zh$ (dashed curves). Also shown at $h \to b \bar{b}$
             with leptonic $W,Z$ decays. The right hand scale indicates the
             number of events per 30 fb$^{-1}$ integrated luminosity (per detector).}
  \label{sigxbr}
\end{figure}

Although the decay mode $h\to b\bar b$ in Eqs.~(\ref{gluon}) 
and (\ref{wwzz}) would be swamped by the QCD background, 
the decay modes to vector boson pairs, 
\begin{equation}
 h\to W^*W^*,\ Z^*Z^* \ \ ,
\label{vv}
\end{equation}
will have increasingly large branching fractions
for $m_h\gsim 130$ GeV and are natural channels to consider
for a heavier Higgs boson. 

In Fig.~\ref{sigxbr}(a), we show the cross sections for $gg\to h$
with $h\to W^*W^*$ and $Z^*Z^*$ versus $\mh$ at $\sqrt s=2$ TeV. 
The leptonic decay channels are also separately shown 
by solid and dashed curves, respectively, for
\begin{eqnarray}
 h \to && \ww \to \ell\nu jj\ \ {\rm and}\ \ 
\ell\bar\nu \bar\ell \nu ,\label{sigww}\\ 
       && \zz \to \ell\bar \ell jj\ \ {\rm and}\ \ 
\ell\bar \ell \nu\bar \nu ,
\label{sigzz}
\end{eqnarray}
where $\ell=e,\mu$ and $j$ is a quark jet.  Although the $\ljj$ mode
has a larger production rate, the $\llnn$ mode is cleaner in terms of
the SM background contamination.  The corresponding modes from $\zz$
are smaller by about an order of magnitude.  At the LHC, the 
$\lpm\nn$ channel is an important discovery mode~\cite{dreiner}.

It is natural to also consider the $h\to \ww$ mode from the $Wh$
associated production in Eq.~(\ref{whzh}).  It was noted \cite{Stange:1994ya}
that associated production with $h\to\ww$ can lead to a unique 
like-sign lepton signature via
\begin{eqnarray}
W^\pm h \to \ell^\pm \nu\  \ww \to 
&& \ell \nu\ \ell\nu\  \ell\nu,
\label{unlikesign}\\ 
&& \ell^\pm \nu\ \ell^\pm \nu\  jj.
\label{likesign}
\end{eqnarray}

The production rates for these modes are denoted by solid curves in
Fig.~\ref{sigxbr}(b).  The trilepton signal is smaller than the
like-sign lepton plus jets signal by about a factor of three due to
the difference of $W$ decay branching fractions to $\ell=e,\mu$ and to
jets.  For comparison, also shown in Fig.~\ref{sigxbr}(b) are $Wh\to
b\bar b\ell\nu $ (solid) and $Zh\to b\bar b\ell\bar \ell$ (dashed) via
$h\to b\bar b$.  We see that the signal rates for these channels drop
dramatically for a higher $\mh$.  Comparing the $h$ decays in
Fig.~\ref{sigxbr}(a) and (b), it makes the gauge boson pair modes of
Eq.~(\ref{vv}) a clear choice for Higgs boson searches beyond 130 GeV.

The purely leptonic channel in Eq.~(\ref{sigww}) has been studied at
SSC~\cite{lnulnu} 
and LHC energies~\cite{dreiner} and at a 4 TeV
Tevatron~\cite{GH}. Despite the difficulty in reconstructing $\mh$ from
this mode due to the two missing neutrinos, the obtained results for
the signal identification over the substantial SM backgrounds were all
encouraging.  More recently for the 2 TeV Tevatron upgrade, there has
been a parton level study~\cite{parton_studies} for the $\ww$ channels
of Eq.~(\ref{sigww}) and a study at the detector level for the purely
leptonic channel~\cite{htz} of Eq.~(\ref{sigww}) and like-sign lepton
plus jets channel~\cite{htz} of Eq.~(\ref{likesign}). The trilepton
signature has been examined for the Tevatron and LHC~\cite{Wells}.

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

The event samples for this study were generated using the PYTHIA~6.023
event generator and SHW detector simulation.  The signal cross
sections have NLO QCD corrections~\cite{19} included and are based
on the the CTEQ4M parton distribution functions~\cite{CTEQ}. For
pair production of resonances, {\em e.g.}  $WW$, PYTHIA incorporates
the full $2\rightarrow 2 \rightarrow 4$ matrix elements thereby
insuring proper treatment of the final state angular correlations.
Similarly for $h\to WW$, the angular correlations between the four
final state fermions have been taken into account. The full
$Z/\gamma^*$ interference is simulated for $ZZ$ production; however,
the $WZ$ process considers only the pure $Z$ contribution.  For Higgs
boson production in association with a gauge boson in Eq~(\ref{whzh}),
the associated $W$ and $Z$ decay angular distributions are treated
properly.  For some samples, such as $\tt$ where the rejection factor
was high, but the cross section was also large, generator--level
preselections were applied to reduce the sample passed to SHW. The
production cross-sections for the principal background processes were
normalized to $\sigma(WW) = 10.4$ pb, $\sigma(t\bar{t}) = 6.5$ pb,
$\sigma(WZ) = 3.1$ pb, and $\sigma(ZZ) = 1.4$ pb.  The measured D\O\
$W/Z + 3j$ rate~\cite{w3jet} was used to estimate the background from
$W/Z\,jj$ with a third jet faking a electron.



