Dear Vladimir:

Thanks for your last email dated Jan. 17th. For the new Preshower design (two scintillator planes sandwiching a lead layer), we are still trying to complete the simulation that determines the plane size, shape, PID performance, etc. And so far we do not have a detailed design drawing yet.

But let's take this opportunity to focus on the support structure of the Shower modules. The engineers at Argonne National Lab are working on designing the support structure and currently we have a few questions:

1) What are the fabrication tolerances for the modules? In other words, how much room should the supporting structure
leave between the modules?

2) The engineers are considering supporting all shower modules by the steel rods that penetrate these modules. Therefore, what is the tension in the rods that are used to hold the blocks together? What are the rod diameters? This
question is getting at how rigid the modules are physically and what we can count on if we are just supporting at either one and/or both ends.

3) In reading some of the modules made by IHEP, it was noticed that the KOPIO design has some "LEGO" bits. Are these still relevant for the COMPASS or our SoLID EC design?

What is the purpose of these "Lego" bits in the KOPIO Design (see Fig.1 in B.S. Atoian /et al/ NIM 584, http://www.sciencedirect.com/science/article/pii/S0168900207021717">http://www.sciencedirect.com/science/article/pii/S0168900207021717).  The concern is that one must be careful to have either all the tension on the Lego bits or none of it there.

4) We are strongly considering a hexagonal shape, since the stacking in pseudo-wedges might be easier. Are there any
problems with this?  My understanding is that there will be 6 extra month of fabrication time and extra time for testing the modules, is that correct? What will be the main properties to be addressed by such tests?

Thanks and looking forward to your reply.

Sincerely,

Xiaochao