\subsection{RICH Upgrade}

\begin{center}
{\bf Rich Upgrade}\\
Contributed by Evaristo Cisbani
\end{center}


Successfully operated in the Hypernuclear Spectroscopy Experiment, the
original Hall A Proximity Focusing RICH detector has been upgraded to
provide an effective pion-kaon rejection at 2.4 GeV/c for the
Transversity experiment \cite{rich:cite1}.

The upgraded RICH reuses most of the original RICH (spare) parts. The
photon detector surface has been enlarged from 0.77 to 1.3 m$^2$, in
order to extend the proximity gap of $\sim 70$\%, without loosing
photons, and consequently improve the Cherenkov angle reconstruction.

The relevant characteristics of the original (old) and upgrades (new)
detectors are presented in table \ref{rich:tab1}.

\begin{table}[hb!]
\centering
\caption[Rich Upgrade: Characteristics of the original and upgraded RICH]{%
The characteristics of the original (old) and upgraded RICH (new).}
\label{rich:tab1}
\begin{tabular}[t]{lcccl}
  \hline
  Component & Unit & Old & New & Detail \\
  \hline
  Proximity Gap      & mm & 100 & 159 & Filled with Methane at STP\\
  Pad Panels         &         & 3 & 5 & \\
  Photon Detector    & m$^2$ & 0.77 & 1.3 & Planar surface of pad panels\\
  FE Electronics     & & 11520 & 19200 & Analog, multiplexed T\&H \\
\hline 
  Radiator Thickness & mm & \multicolumn{2}{c}{15} & Liquid Freon (C$_6$F$_{14}$, n=1.29)\\
  Photon converter   & nm & \multicolumn{2}{c}{300} & CsI film coated on Pad Planes \\
  Pad Panel Size      & mm$^2$ & \multicolumn{2}{c}{$645\times403$} & Rotated by 90$^o$ in new version\\
  Pad Size           & mm$^2$ & \multicolumn{2}{c}{$8\times8.4$}&  \\
  \hline
\end{tabular}
\end{table}

The photo-sensible CsI has been evaporated on the 5 pad panels in July
2008 at Stony Brook University where the INFN evaporation facility is
now operated for the production of the Hadron Blind Detector
components of the PHENIX experiment at BNL.  The results of the
evaporation is reported on fig. \ref{rich:fig2} for the 4th panel (the
other 4 panels show comparable quality); the average measured quantum
efficiency is at the level of 25\%, few percent above the typical
values obtained for the original RICH.
 
Each evaporated pad panel (which must be kept in dry atmosphere), has
been stored in a dedicated chamber continuously flushed with inert
gas.  The compact multi-chamber storage system has been designed for
the optimal on-ground transportation from Stony Brook to JLab.

The evaporated pad planes, the reused liquid radiator vessel and the
new larger multiwire chamber have been assembled at JLab inside the
controlled atmosphere of the existing glove box.

Cosmics data have been acquired in the EEL building to verify the
functionality of the multiwire proportional chamber and related
electronics.

The tested detector has been installed in the HRS detector stack in
October 2008 and connected to the liquid freon recirculation and the
CH$_4$ gas systems.

The very first observed ring is presented in fig. \ref{rich:fig3}.

Detailed calibration and characterization are in progress.

%% ---------

\begin{figure}
\begin{center}
% \includegraphics[width=10cm]{fig/eel_rich.eps}
\showfig{width=\textwidth}{RichUpgrade_eel_rich}
\end{center}
\caption[Rich Upgrade: RICH detector in the EEL building]{%
The RICH detector in the EEL building during the chamber cosmics test,
in August 2008, before installation.}
\label{rich:fig1}
\end{figure}


%% --------

\begin{figure}
\begin{center}
% \includegraphics[width=10cm, angle=90]{fig/Jlab-4_qe.eps}
% \showfig{width=0.9\textwidth, angle=90}{RichUpgrade_Jlab-4_qe}
\showfig{width=0.9\textwidth}{RichUpgrade_Jlab-4_qe}
\end{center}
\caption[Rich Upgrade: Post CsI evaporation, quantum efficiency measurement]{%
Post CsI evaporation, quantum efficiency measurement on pad panel 4
(out of 5) at 160 nm; the 4 plots represent 4 different complementary
regions on the pad panel, approximately corresponding to the 4 plot
areas.  Each curve corresponds to a horizontal scan in the region.}
\label{rich:fig2}
\end{figure}

%% --------

\begin{figure}
\begin{center}
% \includegraphics[width=14cm]{fig/first_ring.eps}
\showfig{width=14cm}{RichUpgrade_first_ring}
\end{center}
\caption[Rich Upgrade: Very first ring observed on the
upgraded RICH]{%
Very first ring, produced by an electron at plateau,
observed on the upgraded RICH during the commissioning of the
detector. Mapping and calibration were not optimized.}
\label{rich:fig3}
\end{figure}



\begin{thebibliography}{1}

\bibitem{rich:cite1} E. Cisbani \etal, \textit{``Upgrade of the proximity focusing RICH at JLab''}, NIM A596 (2008) 44-46

\end{thebibliography}
