1. First Thoughts About Backtracking Performance Assessment and Validation Bruce Schumm UC Santa Cruz July 20 2007 Validation Meeting

2. What is the backTracking (“TRTSeededTracks”) adding to the overall picture? After some exploration, decided that the sensible thing to do is to study via the InDetRecStatistics ntuples (will need to go this route eventually anyway) The following may be more a study of the implementation of backTracking in the InDetRecStat stream than it is of the backTracking itself. I am looking for feedback!

3. Idealize TRT geometry Approximate as straight line in r-z Estimate path-length in TRT Note: Particles can terminate in and emanate from TRT volume Defining “trackable” tracks

4. This crude TRT path-length approximation could easily be improved, but best would be to have the TRT (and SCT. Pixel?) hits for each MC track, and make sure there’s enough to find the track with. “Findable” track definition (start restrictively) Outward-traveling TRT path length > 500mm p  > 750 MeV/c eta< 1.5 Radius of origin * No cut for now * Main purpose of backTracking is to pick up non- prompt tracks

5. Modus Operandi Generate 10 events of Z + jets (Beginner’s Workbook events) Reconstruct twice, writing out two separate InDetRec- Statistics.root output file Without backTracking (“w/o”) With backTracking(“w/”) Make list of all truth particles found by standard tracking (“Tracks” branch of “w/o” ntuple) Look for new particles found by backTracking (“TRTSeededTracks” branch of “w/” ntuple). It doesn’t count if a TRTSeededTrack truth-matches to a particle that was already found by standard tracking.

6. Total found TRT- Seeded tracks: 55 Total “findable” TRT tracks (not already matched to a track: 72 Out of 10 Z + jets events… Sounds pretty good, but let’s look a little closer…

7. For the 72 “findable” particles not already found, only 3 were matched to by TRT-Seeded tracks. What about the other 52 tracks? Track Accounting (out of 52 missed): 37 truth-matched to particles with p  <750 MeV 2 truth-matched to particles with  > 1.5 10 truth-matched to particles that terminate before they reach the TRT (bug in InDetRecStat truth-matching?) 3 have low truth-matching purity (“prob.” < 0.9)

8. A few additional facts… The 3/72 = 4% of particles that are found have an average p  of ~1 GeV/c (somewhat high), and one terminates in the back of the TRT. But not much info from only three particles. If I require that the particle originate inside of 20cm (to make sure that there are available SCT hits to use), the efficiency is 3/33 = 9% – somewhat better, but not spectacular.

9. Fits and Fakes In addition to efficiency, must calculate fake rates to assess performance. Need track fit information to determine meaningful fake rate (do you care about a fake track if it has p  = 0.1 MeV/c, or if it misses the origin by 50 cm?) No track fit information is available for TRTSeeded tracks.

10. Conclusions All of these drawn assuming that I am correctly running and interpreting the backTrack algorithm… 1)No fit information for TRTSeeded tracks; 2)Efficiency in InDetRecStat stream very low 3)May be a bug in InDetRecStat truth- matching (?) 4)Hit information for mcparticles would be helpful!