Development of compact ECC techniques for neutrino-flux measurement

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Neutrino oscillation experiments are the only possible method at present to approach the problem of neutrino mass. In these experiments, neutrino-flux measurement is the key point. Therefore, development of techniques to measure precisely the neutrino flux is an urgent subject in neutrino physics today. In this situation, we have studied a particle detector which is based on techniques completely different from other ordinary electronic detectors, compact Emulsion Cloud Chamber(ECC), for neutrino-flux measurement.(1) We made compact ECCs which had sandwich structure of 1 mm thick lead plates interspaced with emulsion films(42μm emulsion layers on both sides of a 200μm thick plastic base).(2) To observe the behavior of low-energy electrons in an ECC, two ECCs were exposed to an electron beam with the momentum of 2GeV/c, 1GeV/c, 0.5GeV/c, 0.25GeV/c at the Laser-Electron Photon facility at SPring-S(LEPS). By measuring tracks in the emulsion films with a fully automated scanning system, Ultra Track Selector(UTS), exposed electron density in the ECC was found to be 230 electron tracks/cm^2 with background density of 2 tracks/cm^2 in the case of the 2GeV/c electron exposure. The behavior of electrons in the ECC was observed and it was compared with that of pions. We found that identification of an electron track in the ECC can be made with sufficiently high efficiency.(3) A compact ECC was exposed to a 4 GeV/c pion beam at the KEKPS-π2 beam line. We found that momentum of pions can be determined, by measuring multiple Coulomb scattering, with accuracy of 20%.