1. sTGC pad, wire and strip segmentation Daniel Lellouch Weizmann Institute Parameter book: https://twiki.cern.ch/twiki/bin/viewauth/Atlas/NSWParameterBook Physicist’s (ROOT) drawings: https://twiki.cern.ch/twiki/bin/viewauth/Atlas/NSWlayout

2. Large Pivot Confirm Small Confirm Pivot MM Trigger: 3-out-of 4 & 3-out-of-4 11 mm 290 mmWire groups Strips Pad

3. Strips measure θ Strip pitch: 3.2 mm Typical number of strips in a gas-volume : D1/D2/D3: 400/360/360 Therefore main contribution to overall channel number: 280K out of 360K Size of active volumes all designed to hold exactly (n+½) strips. To avoid problems of track hitting inter-strip gaps in more than one layer, strips are staggered across layers: Layers 1 and 3: ½,1,1,1,1,1,1,… Layers 2 and 4: …..,1,1,1,1,1,½ Note: this is not really needed because lack of projectivity does the job since θ●Δz > pitch. (“Maximum shuffling” argument) Strip segmentation

4. Avalanche is late if originates half the distance between two wires, causing inefficiency. Since we want a 3 out 4 trigger, wires have to be staggered in 4 planes of modules to avoid situations with two late avalanches. Reminder: wires measure “φ”. Bending angles and distances involved make this possible in the following arrangement: 0, ¼, ¾, ½ Wire staggering

5. Wire group segmentation Wires are bundled in “groups”, which are themselves staggered in the 4 layers by 0, ¼, ½, ¾. Group size: – D0 : 20 (not read out) – D1 : 10, Δφ = 13/8 mrad at high/low η – D2 : 20, Δφ = 16/10 mrad at high/low η – D3 : 20, Δφ = 10/8 mrad at high/low η VMM channel filling – from 45 to 64 (out of 64 max.) Rates: see slides prepared for tomorrow’s discussion

6. Improving granularity by Pad staggering Pivot Layers 1&2 Pivot Layers 3&4

7. Pivot/Confirm wedges are also staggered wrt each other: 1/4th pad granularity Confirm Layers 1&2 Pivot Layers 1&2 Pivot Layers 3&4 Confirm Layers 3&4

8. Reducing bandwidth inside wedges by pad “fuzzyness” Pivot Layer 2 Pivot Layer 1 Pivot Layer 3 Pivot Layer 4

9. The complete picture Pivot Layers 1&3 Confirm Layers 2&4 Confirm Layers 1&3 Pivot Layers 2&4

10. In real life Pad size is a compromise between : – Number of channels – Individual rate Each quadruplet is built from two face- to-face doublets – η fuzziness achieved for free by Z – φ fuzziness achieved by construction Typical pad height ~80 mm (~25 strips)