Dear Vladimir:

Our colleague Paul Reimer has received the stainless steel rods from CERN. Thanks!

Here I am providing an update on our EC design. I have attached two schematic drawings, the first to show the module layout in the EC (front view), the other to show the layer design. The main changes are as follows:

1) Due to support design considerations, we have changed the modules to hexagon-shape. The hexagon will be 6.25-cm on each side so the total area is about 100 cm^2, matches our original square module design. The 6.25cm includes all light-tight wrappings;

2) The Preshower design is similar to before, but is described briefly here: The Preshower will be made of 2X0 lead followed by 20-mm Scintillators. The lead can be a large sheet as long as it covers the whole area. The Scintillators will be in the same hexagon shape/size as the Shower module. The light from Scintillators will be read out by embedded WLS fibers, which will be all guided to the size of the EC detector, using the space between the EC and the magnet wall, to the field-free region for PMT readout. Due to the length needed, all WLS fibers will be connected to clear fibers using commercially-available 1-1 fiber connectors, somewhere inside the magnet.

(BTW we have not looked into the possibility of using 10-mm Scintillators for the Preshower as you requested, but we will do the simulation soon).

3) We have added a layer of Scintillator pad for photon-rejection purpose, as you suggested. Our simulation does take into account low energy background including photons. This pad does not need to be in hexagon shape. Based on the rates and the readout capacity, the photon-rej Sc pad (PRSP) will be 5-mm thick and cover the whole area from R=85cm to 240cm. It will be divided into 60 segments in the azimuthal direction, into "fan" shapes, and each "fan" will be divided into two segments: Inner pad, R = 85 - 127 cm; Outer pad, R = 127 - 240 cm. This gives a total of 120 segments. The radial segmentation is based on equal-rates.  This 60x2 segmentation is not final, but the total number 120 will be the minimal we use.

4) We assume the readout of the PRSP can be done in a similar manner as for the Preshower: The scintillator pads will have grooves in the back, either by machining or by special molding.  WLS fibers will be embedded, connected to clear fibers, and guided to outside the magnetic field.  Some space must be reserved between the PRSP and the Preshower to guide the WLS fibers from the inner pads.

Please let me know if the above description explain clearly our design. And if yes, would you please provide comments and suggestions for the whole design, as well as a cost estimate for the new PRSP?

Best regards,

Xiaochao