Balloon-borne electron telescope with scintillating fibers

We describe a new balloon-borne cosmic-electron telescope that incorporates a trigger system and an imaging calorimeter. It is designed to observe high-energy electrons with an energy greater than 10 GeV. The rejection of the background protons is performed by using the trigger system in real time and the off-line analysis of three-dimensional shower profiles observed in the imaging calorimeter. The calorimeter consists of scintillating-fiber belts, emulsion plates and lead plates (approximately 8r.1.thick in total). In order to observe the direction of showers, two belts in each depth are set at right angles with each other. Image intensifier is used to amplify the number of photons from scintillating fibers, and CCD camera is attached at the output window of the image intensifier. The telescope was launched at Sanriku Balloon Center, and it was flown for 12 hours at the level altitude. By preliminary analysis, we observed about 700 electrons over 10 GeV under 4g cm ^-2 of average residual atmosphere. The flux of electrons is consistent with previous observations.