Dear colleagues; This is a minutes of the Joint background meeting held on 20-Aug. *Summary of HER background study in BELLE. (Haba) He summarized the current understanding of BELLE background. Most of background observed in BELLE can be explained by three sources; 1)30 keV X-ray from backscttering of QCS-R SR. Responsible to part of CDC noise/leak current or SVDpinDiode (forw) 2)E<5KeV SR x-ray from upstream steering: Responsible to SVD electronics damage. 3)Spent particle background originated from beam-gas interaction in upstream: Responsible to ToF singles, part of CDC noise/leak current especially inner layer or SVDpinDiode (back). Most of CsI background also come from this. Now it is confirmed that background from halo-wall interaction should not be a major source and that spent partcile background seems to fit a vacuum pressure nicely. CDC noise/leak current are now cleary decomposed by using ToF singles as a scale of spent particle into category 1) and 2) quantitatively. *Improvement to be made in thsi summer (discussion) We agreed the following items to be done in this summer; 1)Replace QC2RE chamber (downstream of HER) with new copper made one. 2)20um thick Au foil on the IP chamber and 300um Au plate in front of SVD electronics. Also modify IP chamber to reduce HOM. 3)Set limits on the strength of steering magnets. Establish procedure to change orbit. 4)Modify/add mask on QCS-L chamber to reduce spent particle background. We decided to add a tungsten mask (20rl length) at the left octopus inside EFC cylinder. 5)Reinforce evacuation power in the upstream of HER as much as possible. It is not easy to get drastic improvement in a short time. As a first step, @vacuum gauges will be added. @IR-V-Maks position are equipped with a new Ion pump. We keep improving vacuum condition in future by modifying beam pipe and adding more pumps. 6)Add shiled on QCS cryostat. -- ------------------------- Best Regards; Junji Haba 幅 淳二 (in Kanji) //////////////////////////////////////////////////////////////////// e-mail: junji.haba@kek.jp haba@mail.kek.jp http://bsunsrv1.kek.jp/~haba/private/haba.html __________________________ Particle Physics Division, / KEK, High Energy Accelerator / H / +--A /~B +--A Research Organization. / /__/ /__/ /__/ /__/ Oho 1-1, Tsukuba 305, Japan. / / / / / / / / / TEL. +81-298-64-5334 ----+ / / / / /_-~ / / FAX. +81-298-64-2580