大久保 俊宏


   The JLC(Japan Linear Collider) project is the post-TRISTAN high energy physics program recommended by the High Energy Committee in 1986.
   This project consists of the construction of a 25km-long linear electron-positron collider and the experiment therewith, at an initial center of mass energy around 500 GeV which will eventually reach TeV region.
   The linear collider is a new kind of collider which consist of an electron linac and a positron linac opposing to each other. The collider has no curved sections downstream of damping rings and is therefore free from the energy limitation due to synchrotron radiation.
   The main purpose of JLC is to discover and study the Higgs boson and the top quark, which are the two missing constituents of the Standard Model.
   JLC detector is composed of a vertex detector, a central drift chamber, calorimeters and muon detectors.
   Key technology lies in the calorimeters to measure the direction and energy of jets, the vertex detector to identify heavy-flavored quarks (b-quark in particular), and detectors to measure the momentum and to identify high-energy leptons.
   The Si-PAD detector which is made of finely segmented silicon photodiodes is a part of the calorimeters.
   This paper reports fundamental performance of the Si-PAD detector and results of experiment obtained by the beam test at KEK with a comparison by a Monte Carlo simulation.
   A segment of the Si-PAD detector is tested by radio active β-rays and cosmic-ray muons at first.
   A prototype calorimeter consists of the Si-PAD detector , a pre-shower detector and hadron calorimeters is constructed and tested using a beam of momentum from 1 GeV/c to 4 GeV/c at KEK. Total effective area of the prototype Si-PAD detector is 18 cm × 18 with a number of 216 pads, each of which has a size of 1.0 cm × 1.5 cm.
   Number of particles for electromagnetic showers detected by the Si-PAD detector at the beam momentum of 3 GeV/c agrees very well with that by the simulation within an error of 5\%. The experimental result shows the performance of the electron-pion separation of the Si-PAD detector that a detection efficiency of electrons is 96.4\% with an contamination of charged pions of 9.8\%.