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[FIXED] Tracking + Truth Match Problem [message #14222] Thu, 22 November 2012 09:24 Go to previous message
Klaus Götzen is currently offline  Klaus Götzen
Messages: 293
Registered: June 2006
Location: GSI
first-grade participant
From: *
Dear all,

I'd like to report about a problem I found in simulated event concerning tracking and MC truth match.

The first issue is, that I find from time to time track objects, which appear multiple times in the event. I noticed it on the pid-level, but already after the reco level, these objects are present. This might look like this (analysis level; displayed quantities are: track number in event, 4-vector, charge, PID probabilities, MC truth match index)

trk:0 (-1.06059,0.495762,2.45283;2.72148) -1 PID:0,0,1,0,0 MC:8
trk:1 (0.142945,-0.639217,0.900123;1.12193) 1 PID:0,0,1,0,0 MC:4
trk:2 (0.193793,0.341487,1.30556;1.37045) 1 PID:0,0,0,1,0 MC:6
trk:3 (-0.26782,0.799728,2.97571;3.09607) -1 PID:0,0,1,0,0 MC:7
trk:4 (1.00258,-0.368745,5.14993;5.26141) -1 PID:0,0,0,1,0 MC:3
trk:5 (1.00118,-0.368159,5.14244;5.25377) -1 PID:0,0,0,1,0 MC:3

or this

trk:0 (-0.550406,0.169454,0.525641;0.792111) -1 PID:0,0,1,0,0 MC:8
trk:1 (-0.0351313,0.275942,-0.119804;0.333483) -1 PID:0,0,1,0,0 MC:7
trk:2 (0.0599226,0.085189,0.0741163;0.189264) -1 PID:0,0,1,0,0 MC:7
trk:3 (0.0599226,0.085189,0.0741163;0.189264) -1 PID:0,0,1,0,0 MC:7
trk:4 (0.0599226,0.085189,0.0741163;0.189264) -1 PID:0,0,1,0,0 MC:7
trk:5 (0.0599226,0.085189,0.0741163;0.189264) -1 PID:0,0,1,0,0 MC:7

trk:6 (5.92574,0.770891,34.7574;35.2676) 1 PID:0,0,1,0,0 MC:5
trk:7 (-0.078541,-0.0528536,3.60024;3.60419) -1 PID:0,0,0,1,0 MC:3
trk:8 (-0.250432,-0.622125,7.483;7.51429) 1 PID:0,0,1,0,0 MC:4
trk:9 (0.251804,0.0933929,1.55109;1.58035) 1 PID:0,0,0,1,0 MC:6

What one can see is, that in the frist event tracks 4 and 5 are very similar, having also the same MC index 3. This might be due to tracks broken into tracklets, which are treated as different tracks.

On the other hand, in the second event, there are 4 identical track objects (tracks 2-5), which seem to be true clones.

The second issue is, that there are mutiple reco tracks having the same MC truth index. This might be due to the upper issue, where the clones or very similar tracks have the same index. But I also observe events like the following:

trk:0 (0.607878,0.248934,1.06207;1.25657) -1 PID:0,0,1,0,0 MC:8
trk:1 (0.196574,-0.357057,0.765892;0.87875) 1 PID:0,0,1,0,0 MC:4
trk:2 (0.594232,0.99658,2.77834;3.01412) 1 PID:0,0,0,1,0 MC:6
trk:3 (-0.0748785,-0.0292746,0.268576;0.313172) 1 PID:0,0,0,1,0 MC:3
trk:4 (-0.914007,-0.203599,3.14832;3.28759) -1 PID:0,0,0,1,0 MC:3

trk:5 (-0.338518,-1.15738,3.99636;4.17666) 1 PID:0,0,1,0,0 MC:5

Here tracks 3 and 4 have quite different 4-vectors, nevertheless the MC index is the same (3) in both cases.

I tried to investigate the effect of the multiple tracks issue by removing tracks with 4-vectors deviating by less the 10E-5 in each component by hand.

The results of an analysis of 1000 D+ -> K- pi+ pi+ (+ c.c.) events are shown in the two attached plots. The blue histogram shows all combinations, the red one is the full MC truth matched part.

FIG 1: Combinatorics with original track list. A very spiky histogram is the result.

FIG 2: Combinatorics of the same 1000 events with removed double tracks. The shape looks reasonable now. Also note, that the number of combinations is only roughly 25% of those above.

I'd like to ask the (tracking?) experts to take a look to that issue, having a very significant impact on analysis results.


[Updated on: Wed, 30 January 2013 15:55] by Moderator

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