Hello Pelle,
It would be useful to release this code as a test case.
Norman

From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Hansson Adrian, Per Ola
Sent: Monday, August 26, 2013 6:05 PM
To: hps-software
Subject: Matching truth particle and sim tracker hit

Dear Experts,

I'm doing, what I thought would be, a simple cross-check in my tracking developments that the first SimTrackerHit in the active silicon is at the correct place as predicted by the truth particle momentum .

This is what I'm doing:
- Find SimTrackerHit of first sensor layer associated with a reconstructed track
- Find the MC particle associated with the SimTrackerHit
- Convert the MC particle momentum, and position, vectors into a helix
- Use standard tools to find the path length along the truth particle helix to the z-position of the SimTracker hit
- Use standard tools to find the 3D point on the truth particle helix that corresponds to that path length.

The plots attached shows the residual in bend plane and non-bendplane for each layer (starting from top left). The aida file is also attached. Didn't put proper axis labels but the main point is that the residual for layer 1 (top left is close to zero in the bend plane but has a shift of about 30um and also RMS~40um in the non-bend plane.

Since there is no material in between, and I verified that the truth particle is the correct A' daughter, we would expect this to be zero in the first layer.

Anyone has any idea on why I get this result?

Normal explained to me that the position of the SimTrackerHit is located in the "middle" of the active silicon. Since I'm propagating to the SimTrackerHit 3D position this should not matter but even if I got that wrong (if the SimTrackerHit z-position was somehow wrong) the mean slope is about 25mrad which means that I would get corrections of about 0.025/0.32mm=8um; not enough, I think, to be responsible for this?

It's also strange that it seems to be ok in the bend plane.

/Pelle


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