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\documentclass{chowto}
\usepackage{color}
\title{Design of the HKS water Cherenkov counter}
\howtotype{reference} % ``expert'', ``user'', ``reference''
%\experiment{Name of experiment} % Optional
\author{Yuichi Okayasu}
\category{hks} % Subject area of this document
%\maintainer{Name of person maintaining document} % Optional
\date{May 10, 2005}

\begin{document}

\begin{abstract}
This document describes the purpose of the HKS water Cherenkov
detector and its design parameters. General information on mechanical
installation and electronics setup are also given.
\end{abstract}

\section{Purpose}
Role of the HKS water Cherenkov counter is to suppress protons in a
kaon($P_c$ = 1.2 GeV/$c$ $\pm$ 12.5 \%) trigger on the online
level. In the case of 100 mg/cm${}^2$ ${}^{12}$C target, stuggered two
layors of this counter were designed to separate 0.34 kHz of kaons
from 280 kHz of protons, and $\sim$100 Hz protons are expected to
remain in the trigger. Additional precise particle identification
should be done by offline analysis using beta information derived from
TOF counter.
\section{Design}
One layer of the water Cherenkov counter is consisted of 12 segments.
For each segment, 35${}^H \times$ 15${}^W \times$ 7.5${}^T$ cm${}^3$
effective volume of the Cherenkov radiator {\it i.e.}, water(index:
1.33) is directly contained in a white acrylic diffusion box(3 mm
thick., Mitsubishi Acrylite \# 402) and 2 $\times$ 2''
photomultipuliers(HAMAMATSU H7195$-$MOD) are attached on the two long
sides through 3 mm thick colorless acrylic window(Mitsubishi \#
000). Maximum diffuse reflectance of the diffusion box is 94.8 \% on
458.5 nm incident ray and typical transmittance of the window plate is
$\sim$ 90 \% on the PMT quantum effective wave length region. 50
mg/$l$ Amino G-salt(2-amino-6, 8-naphthalene-disulfonic acid) was
dissolved in $\sim$18 M$\Omega\cdot$cm distiled water as a wave length
shifter. This chemical and its handling is well controlled by Safety
Lab(Chemical assistance team) chemical expert.
\section{Installation}
This counter is installed in front of the last HKS scintillation
counter(HTOF2X) due to its large radiation length.
\section{Electronics setup}
The analog signals from the 2 $\times$ 12 segments $\times$ 2 layers,
totally 48 PMT's were first led to the patch panel behind the HKS
hut. The signals were splitted after upstairs patch panel into TDC
line and ADC line. Since analog signal height is large enough by usage
of the wave length shifter, and also the length of the signal delay
cable is long enough, any signal attenuator is not required. 1/2 of
the signal pulse height from each PMT was recorded as ADC signal. The
remaining 1/2 were first discriminated and splitted into 2 lines
again. The threshold of each discriminator was set to survive kaon as
much as possible. 1/2 were recorded as TDC and scaler information, the
rest were sent to grouping logic for PID.

The HVs of the PMTs were gain matched so that the one photo-electron
peaks were aligned at about the same ADC channels after pedestal
subtraction in the ADC spectra.
\end{document}

% Revision history:
% $Log: water_cerenkov.tex,v $
% Revision 1.1.2.1  2005/05/13 13:42:07  saw
% Initial version
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