1. Optimizing Endcap Navigation
Rick Wilkinson

2. Endcap Compatibility Checks: Old method, CSC & RPC
Propagate to best-matching chamber
Propagate to center of layer
Keep bouncing until a
neighbor is incompatible
Propagate back
to check neighbors
Rick Wilkinson

3. Endcap Compatibility Checks: Old method, CSC & RPC
Propagate to center of layer
Propagate to best-match chamber
Check left neighbor
Check right neighbor
Propagate back up to test neighbor’s neighbor
Rick Wilkinson

4. New Technique Make a DetLayer consisting of two internal DetLayers.
Class’s methods go to the nearer of the two layers first.
No external code changes needed
In CSC, # of propagations per layer goes from 3.8 to 1.2
class MuRingForwardDoubleLayer
: public RingedForwardLayer {
MuRingForwardLayer theFrontLayer;
MuRingForwardLayer theBackLayer; };
Rick Wilkinson

5. Results, Standalone Muons
Endcaps now have half as many propagations
Overlaps still bad, because of 3 seeds
Barrel-barrel, barrel-endcap, and endcap-endcap
Overall Standalone Speedup: ~5%
Half of CPU time spent in propagation
~1/3 of propagation time “short-distance” (2-30 cm)
~1/3 of short propagations eliminated
Rick Wilkinson

6. Conclusions
Factored CSC and RPC overlapping DetLayers into front and back layers.
Eliminates many propagations.
Speeds up Standalone Muons by ~5%.
Rick Wilkinson