This is a very brief minutes of Background meeting held on 25-Oct. 
The meeting
was devoted to summarize the background status of BELLE 
at the start-up of Fall
period with the result of the 22-Oct dedicated beam study.


*EFC status (Lu): 
	EFC count rate is about 10 Hz both for LER/HER @ 200 mA. (was kHz level at the
last summer). EFC count shows a clear quadratic dependence on beam current. 
Very hot spot (F4) observed in the last summer is gone. They see some sectors
are slightly hotter than others, which may be due to some variation of
gain/threshold. They will look into it further.

*SVD status (Tajima):
	"Single bunch" experiment with 10 mA current shows nwo SVD sees so called "30
keV" X-ray 20 times smaller than that in the last summer. This is consistent
with the rough evaluation in terms of copper/aluminum reflection probability and
solid angle change. Low energy X-ray below 10 keV is almost absent again thanks
to "kick angle limitation" in steering magnets of KEKB. 
	Analysis result on MosFET/PINdiode and new radiation alarm scheme/threshold
will (should) be presented in the next meeting.

*CDC status (Uno):
	CDC now can enjoy a higher HER current before. "Single bunch" experiment shows
population around 5 kev in their dE/dX spectra is now 10 times smaller than the
last summer. Hit rate also reduced by 10 times in all layers. Leak current as a
function of HER current also shows almost 10 times improvement (there still
remains lost particle background). Anyway they can go with a HER current higher
than 200mA. 

*ToF status (Kichimi):
	We can safely assume ToF background is a good indicator for a lost particle
background.  He show ToF single rate becomes 2/3 for HER. LER exhibits no change
if we use the average vacuum pressure over the ring as a reference. 
	CDC leak current now shows a beautiful linear correlation with ToF single rate,
which again implies most part of CDC background comes from lost particles in the
October run. He is trying to decompose SR component in CDC leak current by means
of ToF rate as he did in the last summer. The result will be reproted in the
next meeting. 

*CsI status (Sagawa):
	Strong peaks found in both endcap regions in theta distribution of "pedestal
widening"  in the last summer HER data is gone. This is due to the new lead
shield attached on the QCS-L cryostat. Counting rate w/E>10MeV is also reduced
significantly. (half @ 100mA) . Inner most two layers of backward endcap are now
very quiet thanks to the lead collars attached inside of the inner cones of the
endcap detector.   
	Situation for LER is not so different except for the absence of the "hot two
inner layers" of the forward endcap. This is also due to the lead collar inside
the endcap. 

*ZDLM (Uehara):
	ZDLM suffers from 4 times higher background than the last summer. The reason is
nwo under investigation. At higher current of HER (~200mA) slow (40sec period)
oscillation signal are observed on background level. This may due to some orbit
oscillation. 

+++++Next meeting will be held on 9_Nov. from 10:00 am at Rm.325 of 3-Gouakan,
where lost particle background situation are reported more extensively. We like
to ask KEKB Vacuum people to give a report on improvement of vacuum.  
-- 
-------------------------
        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