R & D of a Cosmic Ray Detector with Proton Beams by CERN-SPS

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We have carried out accelerator beam tests for the balloon-borne electron telescope with scintillating fibers (BETS). The detector was transferred to CERN in Switzerland and was irradiated to the proton beams with energies from 30 GeV to 250 GeV.This energy region corresponds to the energy region in which we observed the cosmic-ray electrons. The telescope is capable to identify the electrons and measure the energies by imaging the shower developments with scintillating fibers.The beam tests were carried out at the SPS-T1/X5 beam line in the West Area. Nearly 100 thousands protonns were irradiated under various conditions and the data were recorded, on the digital recoding tapes. The experiment was performed by excellent supports by the CERN staffs. The purpose of the test was completely accomplished within the scheduled dates. By the data analysis, we have confirmed the performance of BETS as following :.The rejection of protons can be performed tby imaging the shower profile..It becomes clear that the protons coming from the side of detector can also be triggered as backgrounds and can be rejected by analysis..The rejection power against the protons is consistent with simulation.We have definetly derived an electron energy spectrum from the balloon data in 1997 and 1998 by adopting the proton rejection power. A new method for higher rejection power will be devldped using the beam test results.