BLTWG Meeting 03/26/2009
- Time: 9:30 EST
- Place: EVO and ESNET (with telephone bridge)
- Connecting: instructions are here
- Present: Richard J., Igor S., Jim S., Tim W., Eugene C., Franz K, and Alex S.
- 1 Agenda
- 2 Notes by R. Jones
- Tagger design internal review at JLab - Jim
- Microscope background rates estimates - Alex
- Checkout of updated photon beam simulation geometry - Richard
- Update on the spring 2009 CHESS run - Richard
- Update on phototube tests - Franz
- Review of working group manpower situation - Richard
Notes by R. Jones
Tagger design internal review at JLab
Tim has suggested that our tagger magnet specification be shown to an internal review panel at the lab, and have it critiqued before prospective vendors do. There was unanimous support for this idea. Tim and Jim have assembled a short list of people who would be good candidates for the panel, and will work with the Hall D group leader to arrange the best time. Middle to late May is currently being considered. Tim is going to draft a charge for the review. The presentations will be made by the engineering team led by Tim, but it was thought to be useful if Franz and Richard could be present, either in person or by video conference. RJ will send to Tim a list of preferred dates for the review.
Tagger background rates estimates
Alex has finished his technical note on tagger background simulations. It has been uploaded to docdb under gluex-doc-1228. New figures were shown for the updated background estimates for the microscope counters. As shown at the last meeting, the updated backgrounds in the fixed array vary from 10% of the signal rate near the end-point to about 4% in the mid-energy range, decreasing to 1% at the low photon energy end of the array. In contrast, the updated backgrounds in the microscope are about 0.5% of the signal rate in the region of the coherent peak at 9 GeV, similar to what was presented at the tagger review. Alex pointed out that his simulation includes a rectangular extension to the downstream end of the tagger vacuum chamber. Without this extension, the fixed array counters would have substantially more than 1% background at the low-energy end. This extension has not been implemented in the engineering drawings yet, but the engineers are aware that it is desired and will coordinate that update with the accelerator design people who are primarily responsible for the electron beam line from the tagger to the dump.
Checkout of updated photon beam simulation geometry
Richard is still working on verifying the HDDS geometry for the photon beam simulation. The contents of the collimator cave are finished, and the pair spectrometer is in progress. Improvements include a more refined description of the structure of the permanent magnet used as a sweep downstream of the primary collimator, and a refined description of the pair spectrometer geometry. So far, none of the changes are of the sort that would require rerunning the beamline background simulations.