1. Second Coordinate A pitch for Small Angle Stereo
V. Polychronakos
BNL

2. Second Coordinate 2D detector, Small Angle Stereo, ???
Need to decide soon
Affects detector design
Number of Electronics Channels
Readout
Trigger Strategy/Algorithms
Cost
What is required by the new Trigger Logic
Provide R,f with resolution 0.02 x 0.02 [eta, rad]
dq is also sent to Sector Logic, will be used in Phase 2 to improve PT resolution for sharper thresholds.
dq cut implemented in NSW logic
0.02 rad at R=1m implies f resolution of order 10 mm for trigger

3. Advantages of Small Angle Stereo
Significantly fewer channels  cost, power, cooling, space on det.
Eliminates need for connections in radial boundaries
Simpler Micromegas fabrication, lower complexity, cost
Much smaller area of confusion because of ghosts
Straight forward R, f calculation (pair of addresses defines params)
More importantly: Full charge used
For efficient trigger and micro-TPC operation it is important to be able to trigger on single electrons
Even at very high gain (40,000 for example) charge in the input of VMM is 1.6 fC (we collect ~1/4 of the total charge in 50 nsec).
With a typical noise of ~0.5 fC this requires triggering at ~ 3 sigma noise
With two coordinate detectors we get half of the charge, difficult/impossible to trigger on single electrons

4. Small Angle Stereo (Some numbers)
F resolution for a stereo angle q is given by:
Where: sh is the resolution in the h (radius) coordinate
Even with a 3 degree stereo the resolution is more than adequate
Degradation of the main coordinate in the stereo view is negligible
Stereo Angle[deg]
Trigger [sh = 500 mm]
Off-line [sh = 100 mm] 3
9.5 mm
1.9 mm 4
7.2 mm
1.4 mm 5
5.7 mm
1.1 mm

5. Some comments One view can be parallel to the radial boundary
Perhaps not all 4 pairs need to be in stereo?
“Area of confusion” given by:
Where p is the strip pitch
For 3 degrees and L =1.5 m
w = 80 mm