sTGC pad, wire and strip segmentation

Daniel LellouchWeizmann 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

Large Pivot ConfirmSmall Confirm Pivot

MM

Trigger: 3-out-of 4 & 3-out-of-4

11 mm

290 mm Wire groups

Strips

Pad

• 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

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

0.5 1 1.5 2 2.5 3 3.5 4 4.50

0.25

0.5

0.75

1

1.25

1.5

1.75

2

Layer number (up to scale)

Wir

e pi

tch

(up

to s

cale

)

Wire staggering

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

Improving granularity by Pad staggering

Pivot Layers 1&2

Pivot Layers 3&4

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

Reducing bandwidth inside wedges by pad “fuzzyness”

PivotLayer 2

Pivot Layer 1

Pivot Layer 3

PivotLayer 4

The complete picture

Pivot Layers 1&3

ConfirmLayers 2&4

ConfirmLayers 1&3

PivotLayers 2&4

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)