1. 1 Coordinate Detector: prototype design The Coordinate Detector (CDET): Three independent vertical planes with 15 cm plastic shield in front, all planes as close as possible One detector plane consists of four sections each covering 96x116 cm 2 The active element of each section is a stack of 0.5x3 cm 2 scintillator bars, split in half, viewing the target WLS fibers run through holes in the bars and transmit light to H8711-10 16-channel PMT The prototype reported here, will represent mechanically one section of the CDET: Instead of using 5 mm thick scintillators we will use plastic bars cut from 3/16” acrylic sheet; no holes in the bars The fibers will run from the end of the bars to the cookies No light sealing

2. 2 CDET prototype design Prototype with the cover removed Front plate: ¼” aluminum Six vertical stacks (each 32 bars), split in half Each stack is strapped to the front plate at different positions to make transition between the sections The straps run through holes in the front plate 1/2” smooth polyester straps, 0.5 mm thick, with seals niches in the stacks for straps

3. 3 Connection between detector sections End of the front plate of one section inserted into the other section Cover on the back attached to the two cross-bars Light tightness using black tape and sealant between sections (front and back plates), on the cover edges and in the openings for the straps End plugs on the top and bottom sections (not in the present design) Scintillators removed from the left half to see the openings for the straps Fibers not shown All dimensions in mm

4. 4 Fibers to PMT connections Cross-bar (1/2” Al) attached to front plate Cookies with 16 holes in which fibers are glued PMT holders with PMTs glued to them

5. 5 Cookie and PMT holder attachment PMT is glued in a plastic PMT holder PMT holder is firmly attached with four screws to the cross bar while the PMT goes through a hole sticking outside of the cross-bar by 1.5 mm The WLS (not shown) are glued in the cookie inside 16 holes The cookie is attached to the front plate with four screws with springs (not shown) Two dowel pins in the cross bar center the positions of the PMT holder and the cookie (along red line)

6. 6 Cookie and PMT holder attachment PMT holder is firmly attached with four screws to the cross bar while the PMT goes through a hole sticking outside of the cross-bar by 1.5 mm The cookie is attached to the front plate with four screws with springs (not shown) Two dowel pins in the cross bar center the positions of the PMT holder and the cookie

7. 7 Outlook Prototype of one section of the CDET designed to test mechanically the concept: The rigidity of the whole construction (trying to minimize distance between planes using only ¼” front plate) The cross-bar: at some places it has 1.5 mm wall The technique of gluing PMT to the PMT holder and the fibers to the cookie The attachment of the cookies (with fibers already glued) to the cross-bar Stacking the bars at the right angles and strapping them to the front plate Tolerances: gluing the PMT to the PMT holder, centering the PMT to the fibers To design tools helping all of the above operations The technical documentation is close to completion, expect it in few weeks