Search for neutrino oscillation by using emulsion trackers

点击翻译按钮获取中文摘要

The CERN-WA95/CHORUS experiment is designed to search for neutrino oscillation in the νィイD2μィエD2→νィイD2γィエD2 appearance channel with the CERN SPS Wide-Band Neutrino Beam. For the CHORUS 1996 and 1997 runs, we proposed to install three large emulsion trackers (ET0, ET1 and ET2) into the CHORUS apparatus. The aim is to improve the momentum accuracy and to extend the range of measurement from 10 to 30 GeV/c, a kinematical domain which includes an additional 26% of the γィイD1-ィエD1→hィイD1-ィエD1 X events. The ET construction, installation, surveys and data taking during the beam exposure were performed successfully in cooperation with colleagues from Brussels and other groups in the CHORUS collaboration. The emulsion sheets for the ETs were replaced twice a year to limit the background due to passing through tracks. The relative alignment among the three ET planes is based on data of beam-associated muons which passed through the detector while the magnet was off. As a result of the automatic scanning and measurement, after the alignment procedures, it was found that deviation of the muon tracks on ET2 from the ET0-ET1 prediction has a δ〜100μm. This value can be explained by CT〜25μ position resolution for each ET plane. The position resolution is about one order of magnitude better than those of conventional detectors. Performance on the momentum measurement of the emulsion trackers is estimated by using beam muon data which were taken with the magnet being on. By comparing with the momentum measured by the muon spectrometer system, the momentum resolution of the emulsion trackers was evaluated to be Δρ/ρ〜 ィイD8(0.22)ィイD12ィエD1+(0.010×ρ(GeV/c))ィイD12ィエD1ィエD8, which confirms that the momentum of hadrons can be determined up to〜30 GeV/c, as was designed. The emulsion trackers will be used in the CHORUS phase II analysis to discriminate real γ candidates from various backgrounds.