Minutes of the BEAST meeting
Thursday April 30th 8:00a.m. JST

  • Structure:
    Rosen showed updated CAD plots of the structure. The details of the support were discussed. As noted earlier, supporting SS rods extend from BEAST to an intermediate ring which is then attached to the CDC endplates. There are three rings of holes on the inner part of the endplate:
    ring 1 of holes has diameter 162 mm
    ring 2 of holes has diameter 176 mm
    ring 3 of holes has diameter 247 mm
    The holes in ring 1 are also known as "Yamada's holes". The intermediate ring from BEAST currently is attached to the second ring and covers the holes in ring 1. Rosen noted that this can be changed easily if necessary.
    Rosen's trip to KEK will begin on May 28th. He will devote a week to BEAST mechanical issues and will meet with Haba and Yamada to clarify issues such as those discussed above.

  • Simulation:
    Sahu presented updated simulation results including the shielding effects of moveable masks on the new lattice. The new results are:
    Rates incident on BELLE
    e+ Brem335 kHz
    e- Brem36 kHz
    e+ Coul84 kHz
    e- Coul6 kHz
    The addition of the e- moveable mask substantially reduces the e- Brem background.
    Sahu checked the sensitivity of the simulation to physical cutoffs:
    E_cut
    0.10.050.02
    e+ Brem315 kHz335 kHz332 kHz
    e- Brem40 kHz36 kHz36 kHz
    Theta_cut
    1 mrad0.5 mrad0.1 mrad
    e+ Coul75 kHz84 kHz82 kHz
    e- Coul7 kHz6 kHz6 kHz
    The second values are the nominal ones. The simulation appears to be in the "plateau" region.
    A request to understand better the details of the discrete sources of e+ Brem was made. "Why are the peaks so sharp ? How does DECAY TURTLE work ? Can we see typical trajectories from the discrete sources ?"
    The new background files from Sahu's generator will be sent to Bozek for incorporation into BELLE GEANT.

  • Pressure bump studies
    More coordination with the accelerator division was requested. If only a small number of pumps can be adjusted, what is the optimal location for these pumps to diagnose the background ? A formal proposal for pressure bump studies should be submitted to the vacuum experts in mid-May.

  • Proportional Chambers
    A PC board protoype for the readout circuit (there will be a DC measurement and a pulse measurement) was submitted and will come back next week.

  • Diodes
    Have not submitted PC board design yet.
  • Cd-109 sources
    To be decided after golden week. Are 22 mm diameter sources acceptable ?

    A new meeting time will be investigated and will be announced later.