1. ACD Analysis Status
Work done by Taro Kotani. Much help from Heather. Advice from Ormes, Hartman, Moiseev, Norris, Ritz, Thompson…
Main issues:
Hermeticity requirements
Segmentation of back row(s)
Revisit hit efficiency requirements
Revisit electron rejection

2. Hermeticity requirement
In principle, not a problem. But no one has ever flown a segmented ACD.
Scale is set in part by hit efficiency requirement
What is the impact of cracks?
Rerun background rejection analysis and plot rejection as a function of crack width (note, tile inefficiency was included in AO analysis)
what are these??!

3. What are these??
Due to evolving knowledge and time constraints, for AO analysis the background rate calculations included an estimate of the proton splashback and re-entrant albedo, but the spectrum was that of the galactic cosmic rays. (arguably a pessimistic assumption).
This is the first look at low-energy protons in the simulation.
Some questions to address here…
is the simulation sensible?
if not fix it; if yes, work on filter design.

4. What to do?
This is an important question to investigate. It will be interesting to see the G4 simulation.
It does not have a significant impact on the ACD design questions – these are bigger issues for the instrument and they won’t drive the hermeticity, efficiency, segmentation, etc.

5. Remaining Issues
Segmentation of back row(s) driven by high energy requirements (AO plan had high segmentation to avoid backsplash when the ACD is needed in the analysis). Primary driver is electron rejection.
Work is just starting on electron rejection. Worst energy decade appears to be 1-10 GeV. The electron rejection also drives the efficiency requirement.