Minutes of the BEAST meeting
Thursday April 22nd 9:00 JST

(Minutes recorded by J. Haba).

  • *BEAST results (Browder, Moffit):

    With tuning of masks in arc and at IP and improvement of the vacuum etc., the background level at the location of the SVD is now not so bad. The expected background for the initial operation condition (500mA(LER)+250mA(HER)) is 200-300 krad/year level. Conditions during injection are still unstable and there are still occasional"very bad" injections. To avoid exposing BELLE to such bad injection, we have asked the KEKB crew to develop an injection tuning scheme with low current in future operation. Another good news is the Sydney diodes which are installed in the BELLE for radiation monitoring were proven to work in BEAST even after exposure of more than 100krad.

  • *BEAST SVD Ladders(Tajima) :

    He showed the SVD data taken in transparent mode with 1 micro sec shaping time. He found that 1)SVD is still alive after an exposure of more than 100 krad (He believes SVD ladder got more than measured by the dose monitor which is placed outside of SVD quadrant.) with a S/N ratio better than 10. 2)The S/N ratio dependence on the instantaneous dose rate is small and up to the dose corresponding to 350mA(HER), S/N is less than 10. 3)Occupancy with the threshold of 0.5MIP is less than 8 % up to the dose corresponding to 350mA (HER).

    His tentative conclusion is that SVD can be operated reasonably in the initial condition of BELLE experiment with 1 micro-sec shaping time. The modification of the shaping time is necessary and pre-trigger/fast clear scheme should be prepared in the frame work of whole DAQ system. SVD group should initiate group-wide action immediately. The new scheme should, of course, be ready and proven to work by May 24th.

  • *CDC condition (Uno) :

    He discussed the limits on chamber lifetime due to acculumated charge on the wire and consideration on deadtime due to high counting rates. The CDC group will use their CDC as a radiation/background monitor (ie with reduced HV). It was pointed out that background monitor should be independent of the main DAQ as much as possible. CDC people should make some efforts to provide background information even with using CDC itself.

  • *CsI condition (Kuzumin) :

    The condition for CsI became much better in the last BEAST run. The dose level is acceptable. The broadening of the pedestal due to pile-up is around 1 MeV/crystal, which is still large but not critical. They will install some special pure-CsI counters with FM-PMT at the ECsI inner ring to provide both fast analog signal and instantaneous dose rates.

  • *KLM (Abe) :

    There are no reliable estimates of expected background in KLM. Some CsI counters placed on the KLM during KEK-B commissioning indicate that photons with higher than 1.5 MeV energy produced a flux of a 500Hz/cm**2/nTorr/A deposited in CsI. The RPCs in the KLM can tolerate a flux up to 0.2Hz/cm**2 We do not know how much the detection efficiency RPC has for 1.5 MeV photon. Anyways, they plan to install a concrete shield to limit an inner aperture of the existing C shape shield. in this summer. By that time, some of the outer layers of EKLM may be turned off.

  • *SR study result (Bondar) :

    They found that SR contribution is not serious at the present level of background.

    In the near future, there will be a series of discussions on hadrware and software aspects of radiation resistance in BELLE.

    PS: After the meeting, I asked the CsI people to set up a dedicated CAMAC crate which collects scaler counts, DC levels by slow ADC, etc. This crate will be operated by an Independent PC and the data will be posted on NSM. With the information from other systems like SVD monitor or KEKB, a post-BEAST PC will make monitor/logging systematically.