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{\bf SUMMARY: \\
L2 PREPROCESSOR FOR THE \\
Si DETECTOR}\\
(20 November 1997)\\
\end{center}
\bigskip\bigskip
{\sl Suggestion to the collaboration}:\\
\noindent {\bf Expand/modify  present L1 and L2 lay-out so that addition of a L2
preprocessor
for the Si vertex detector is possible.}\\
\bigskip\bigskip

\noindent Tasks carried out by this device:
\begin{itemize}
\item finds hit clusters in Si detector
\item finds tracks in Si detector (in roads provided by CFT)
\item determines track parameters
\item finds z\_vertex from 90\Deg Si hits
\item ships information to global L2 processor for decision
\item ships z\_vertex and hit cluster information to L3
\end{itemize}
\newpage
{\bf Physics benefits:}
\begin{itemize}
\item use of Si detector hits in track fit\\
\imply improve momentum resolution\\
\tab    \imply sharper $p_t$ thresholds,\\
\tab    \tab  E/p for electrons at L2;\\
 \tab  -- potentially benefits any trigger
\item trigger on tracks with high impact parameter \\
    \imply trigger on events containing $b$-quarks;
\begin{itemize}
\item provides very powerful handle for background rejection, with good signal
efficiency, for
many interesting physics channels:
\begin{itemize}
\item $B$-physics,
\item $Z \to b \overline b$,
\item Higgs$\to b \overline b$,
\item $t \bar t$,
\item single top
\item $\ldots$\\
\end{itemize}
\end{itemize}
\item use Si detector (90$^\circ$ stereo) information for fast
$z$-vertex position\\
    \imply
        sharper electron and jet $p_T$ thresholds at L3,
%    \     beam tilt $\rightarrow$ need z for impact parameter determination;
\begin{itemize}
    \item benefits any trigger
\end{itemize}
\item Hit finder for L3 \\
    \imply save processing time in L3 by providing
    hit positions for $r/\phi$ and stereo (both 90$^\circ$ and 2$^\circ$),
    making use of Si detector information at L3 possible or more efficient
\end{itemize}
\newpage
\noindent Note:\\
{\sl Decision on providing possibility to add STTpp must be made now,
so that trigger lay-out can be frozen.}
\bigskip\bigskip


\begin{itemize}
\item although no  detailed technical design available, we have some basic idea
how to build STTpp;
\item have basic understanding of expected performance;
%\item
%{\bf
\item many good reasons why we should have STTpp\\
(or foresee possibility to add it):
(or foresee possibility to add it):
\begin{itemize}
\item have evidence that it can provide powerful tools for background
rejection\\
\imply extends physics reach;
\item may need additional handles for physics that we haven't thought of;
\item having more refined information available at trigger level can only be
beneficial;
\item it would be unwise to deprive experiment of this potential capability to
widen physics reach.
%}
\end{itemize}
\end{itemize}


\newpage
{\bf available \DZ notes:}
\begin{itemize}
\item
\DZ Note 3312:
   ``Benefits of a Silicon Vertex Trigger for $t \bar t$ Events'',
         by  Fr\'ed\'eric Stichelbaut (September 1997);

\item \DZ Note 3318:   ``Studies of SVT Trigger using SUGRA Four b Quark
Signature'',
        by   Doug Norman  (September 1997);

\item  \DZ Note 3321:  ``Towards a Run II Trigger for $p \bar p \to W +
$Higgs'',
          by  John Hobbs  (October 1997);

\item  \DZ Note 3338:  ``Primary Vertex Finding at Level 2 using the Silicon
Vertex Detector'',
          by  Meenakshi Narain and Sudhindra Mani  (October 1997);

\item  \DZ Note 3339:  ``Triggering on $Z \to b \bar b $ Events in Run II'',
          by  Meenakshi Narain  (October 1997).
\item \DZ note 3354, ``Study of Triggers for $B$ Physics in Run II'',
Meenakshi Narain, Fr\'ed\'eric Stichelbaut, Andrzej Zieminski (November 1997);
\end{itemize}
{\bf \DZ notes in preparation:}
\begin{itemize}
\item \DZ note on track finding and fitting algorithm,
by Phil Gutierrez and Eric Smith;

\item \DZ note on triggering on single top, by Terry Heuring;

\item \DZ note on STT performance, by Terry Heuring and Dan Karmgard
\end{itemize}


\end{document}
 
