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Briefly, what does this PR introduce?
This pull request modifies the calculation of the seed charge for real seeding for particles generated off the beam axis.
The diagram below shows the proposed change
Here is some statistics to validate this request:
N=10k events, muon with eta -4 to 4, and momentum 0.5 to 20 GeV
Negative muon at (0,0,0)
Total seeds: 25774
Wrong charge seeds (pre-fix): 301 (1.2%)
Wrong charge seeds (post-fix): 224 (0.87%)
Negative muon at (1,0,0) mm
Total seeds: 25521
Wrong charge seeds(pre-fix): 5407 (21.1%)
Wrong charge seeds(post-fix): 230 (0.9%)
Positive muon at (1,0,0) mm
Total seeds: 27688
Wrong charge seeds(pre-fix): 5376 (19.4%)
Wrong charge seeds(post-fix): 368 (1.3%)
This shows that the results are stable for particle generated at z=0.
for particles generated off the beam axis, the results improve significantly for both positive and negative muon.
What kind of change does this PR introduce?
Please check if this PR fulfills the following:
Does this PR introduce breaking changes? What changes might users need to make to their code?
none
Does this PR change default behavior?
yes, for real seeded tracking