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SpacePoint builder assumes that tracks come as straight lines from the IP #57

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tmadlener opened this issue Oct 12, 2021 · 1 comment

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@tmadlener
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The other missing space points seem to happen, because of the assumption of the straight track line from the IP, as @gaede has already suspected...

Here is the one example:
If one calculates intersection point, with respect to the straight line coming from the IP, one gets space point which exceeds the boundary of the sensor and is being reasonably rejected, as firing strips are too far away for such hit to exist if the actual track was coming from the IP. (red square - rejected space point)

One can see that the track comes from very different angle from which it is possible to fire these strips simultaneously.
(large blue squares - SET SimHits).

image

From discussions with @gaede, ideally one would need to take into account helix direction to produce proper space point, however, it is not trivial how to do so, as DDSpacePointBuilder is executed prior to the track fit processors..

Also there are hits, that could be fixed by slightly increasing the tolerance... But one need to take care not to include too many ghost hits, which may be not very properly defined inside DDSpacePointBuilder

Originally posted by @dudarboh in #55 (comment)

@dudarboh
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Just a minor comment,

Increasing the tolerance as a quick dirty fix will produce space points for us, but in cases as on the example above, the position of these space points can be too far off from the true position of the simHits.
So it is questionable whether such a "fix" will be useful or harmful...

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