Efficiency and Purity Studies Outside the VXD:

Applying AxialBarrelTrackfinderZ and GarfieldTrackFinder

By: Tyler Rice, Chris Meyer

August 21, 2007

Event and Particle RestrictionsData Sample: ZPole bbar events

Event Requirements• Thrust value to exceed 0.94• Cosine theta of the thrust axis to be less than 0.5 in magnitude

Particle Requirements• Not Backscatter• Charged, Intermediate or Final State• Path-length exceeds 500mm in magnitude• Transverse momentum above 0.75GeV• Cosine theta less than 0.7 in magnitude• Radius of origin less than 1200mm in magnitude

Reconstructed Track Requirements• DCA < 100mm• Pt > 0.75 GeV/c• Cosine theta less than 0.8 in magnitude

Procedure• Methods written into Garfield which determine the MC Particle associated

with a found track• 10cm Z segmentation applied in both AxialBarrelZ (Lori Stevens) and

Garfield Trackfinders (ABTFZ and GTF).• Methods written into ABTFZ to define the minimum number of layers

necessary for a track to be found, this was then varied between 4 and 5 layers.

• Events which pass the acceptable criteria are passed first into a cheater which removes all MC Particles originating within 2cm of the origin (these are assumed to have been found by another algorithm). The remaining list is then passed into ABTFZ, which further removes found MC Particles, and outputs the final list into GTF, which applies calorimeter assisted tracking to find the remaining tracks.

• Histograms created with the kinematic properties of found, fake, and missed particle tracks. A “found” track requires at least 80% purity (either 4/4, 4/5, or 5/5 matching hits with an MC particle).

Total Event and MC Particle List

Figure1: Total number of events, out of 1000, which pass the event test stated above.

Appx. 26%

Figure 2: Total number of MC Particles passing our restrictions (289), plotted as a function of pT

Figure 3: Total MC Particles plotted as a function of their respective number of hits on the five central tracking layers.

Figure 4: Total MC Particles plotted as a function of radius of origin. 35 particles have a

radius of origin outside 460mm (radius of the second layer)

Efficiency

ABTFZ Followed by GTF Requiring a Minimum 4hits in Either to Reconstruct a Track

*Note* Figure 12 reflects a simple study that was done regarding 3 hit Garfield tracks, in which the GTF was set to

a minimum 3hits and ABTFZ kept at 4hits.

(10cm segmentation)

239 out of 289 Particles were Found, Which Equates to 83% Efficiency

Figure5: Total number of MC particles found by ABTFZ (234/289) as a function of radius of origin (Rorg). All of the found particles have an Rorg under 460mm.

Figure6: Total number found by GTF, only 5/289 total found tracks (2%). Again, all found Rorg lie under 460mm

Figure7: Missed MC particles with Rorg. 35 of these lie outside 460mm.

Eliminating all particles which originate outside 460mm (ones which leave

at most 3 hits), we achieve 94% efficiency.

Missed MC Particles

Figure8: Total missed MC particles vs. transverse momentum. We see a spike right around 0.75 (the minimum allowed pT)

Figure9: Total missed particles vs. number of hits. Only 7 of these are 4 or 5 hit tracks.

Missed MC Particles with 460mm Rorg Cut

Purity

ABTFZ Followed by GTF Requiring a Minimum 4hits in Either to Reconstruct a Track

(10 cm segmentation in ABTF and GFT)

27 out of 266 ABTFZ Reconstructed Tracks were Fake Tracks. This equates to ~90% Purity for ABTFZ

Figure10: Total number of fake reconstructed tracks (purity below 75%) plotted vs. transverse momentum. We again see a higher amount of fakes at low pT.

9 out of 15 GTF Reconstructed Tracks were Fake Tracks. This equates to ~40% Purity for Garfield

Figure11: Total number of fake reconstructed tracks (purity below 75%) plotted vs. transverse momentum for the Garfield Trackfinder. We again see a higher amount of fakes at low pT.

When letting in 3 hit (& 1 stub) tracks from Garfield, 18 out of 39 tracks are fake. This equates to only about 54% purity.

Figure12: Total number of reconstructed 3 hit tracks. Fake tracks are plotted with “0” and high purity tracks with “1.” At the moment, there are just too many fake 3 hit non-prompt tracks to be useful.

Efficiency

ABTFZ Requiring a Minimum 5hits to Reconstruct a Track Followed by GTF Requiring a Minimum 4hits

210 out of 289 Particles were Found, Which Equates to 73% Efficiency

Figure13: Total number of MC particles found by ABTFZ vs. radius of origin (Rorg). All of the found particles have an Rorg under 460mm.

Figure14: Total number found by GTF, 66 out of 210 total found tracks. Again, all found Rorg lies under 460mm

Figure15: Missed MC particles with Rorg. 35 of these lie outside 460mm.

Eliminating all particles which originate outside 460mm (ones which leave at

most 3 hits), we achieve 83% efficiency.

Missed MC Particles

Figure16: Total missed MC particles with Rorg < 460mm, vs. transverse momentum. Again, we see a large majority occurring at low momentum

Figure17: Total missed particles with Rorg < 460mm vs number of hits. About 30 of these are 4 or 5 hit tracks

Missed MC Particles with 460mm Rorg Cut

Purity

ABTFZ Requiring a Minimum 5hits to Reconstruct a Track Followed by GTF Requiring a Minimum 4hits

8 out of 74 GTF Reconstructed Tracks were Fake Tracks. This equates to ~90% Purity for GTF

Figure18: Total number of fake reconstructed tracks (purity below 75%) plotted vs. transverse momentum for the Garfield Trackfinder. We again see a higher amount of fakes at low pT.

ABTFZ 4 Hit Minimum

ABTFZ 5 Hit Minimum

Found MC 239 (94%) 210 (83%)

Missed MC 15 (6%) 44 (17%)

Fake Tracks

Garfield

9 8

Fake Tracks

ABTFZ

27 0

For Rorg < 460

Conclusions (10cm Z Seg.)• The addition of GTF provides a modest increase in efficiency/purity• One reason GTF is missing the 4hit tracks that ABTFZ does not

find may be because the tracks do not enter the calorimeter (further study on this will be done). A possible solution to this would be to run ABTFZ again after GTF with a 4hit minimum. Our hope is that this will find the remaining 4 hit tracks, but keep the number of fakes down.

• The purity of 3 hit tracks in GTF is essentially too low to use. Can we do anything about this?

• We are now working on an ABTFZ and GTF combined z-segmentation study.

• We are also looking into the possibility of extending ABTFZ into the vertex detector.

Thanks for Your Time!

The End