KamLAND, a large size liquid scintillator detector for anti-neutrino detection, has observed the reactor neutrino oscillation and geo-neutrinos since its operation started in 2002. The outer detector (OD) is a water Cherenkov detector with 3,200 m3 of water and 225 Kamiokande-PMTs serving as the veto counter against the cosmic-ray muons. Muon tagging efficiency of the OD has been decreasing since 2010 because of a gradual increase of PMT failures, which results in the increase of muon-induced backgrounds. We have carried out a refurbishment of the OD from January to April in 2016 by replacing the PMTs and improving light collection in the less-sensitive equator region. As a result, we achieved a recovery of the OD detection efficiency of muons equal to 99.8%.
|Journal||Proceedings of Science|
|Publication status||Published - 2016 Jan 1|
|Event||38th International Conference on High Energy Physics, ICHEP 2016 - Chicago, United States|
Duration: 2016 Aug 3 → 2016 Aug 10
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