Pixel Endcaps in the LoI (Cartigny) Layout

The drawings below show 3 possible types of pixel endcap disks in the LoI, or "Cartigny" layout of the upgraded inner tracker. The original Cartigny layout called for six disks, at the z positions shown in the table below, with outer active radius of 315mm and inner active radii of 135mm (disks 1-4), 175mm (disk5) and 215mm (disk 6). These specifications can not be met exactly with the current module designs and assuming the simplest possible disk layout (shown below), where all modules are fixed directly to the front and back surfaces of a flat disk.

The closest match to the requested dimensions are illustrated in the drawings above. These disks use 'quad' modules (modules built on 4 FEI4 chips in a 2x2 grid placement) and 'hex' modules (built on 6 chips in a 2x3 grid). Disks 1-4 would have the 'QHH' geometry shown in the leftmost picture ('QHH' for Quad-Hex-Hex as the innermost ring is made of quad modules and the middle and outer rings are made of hex modules). Disk 5 is QQH and Disk 6 is QH. This results in the dimensions shown in the table below:

• 0.45mm gap between adjacent FEI4s in a module
• sensor dead edge 0.2mm radially
• a hex module is 61.3mm long radially
• a quad module is 40.85mm long radially
• >0.2mm gap required between adjacent modules on a disk, to isolate HV

LoI backup document

The pixel disk backup document for the Phase-II Letter of Intent can be found here: http://cds.cern.ch/record/1515010/files/ATL-UPGRADE-PUB-2013-004.pdf