Characterization MC Particles Missed by Axial-Barrel

Reconstruction & Obtaining Perfect Efficiency

Using Zpolebbar Event File

By: Tyler Rice

Review of MC Particle Requirements

• Radius of origin beyond the VXD (2cm) and below 40cm• Not backscatter off the calorimeter• Either Intermediate or Final State with a path length

exceeding 50cm• Transverse Momentum beyond 0.75GeV• Cosine of theta is below 0.7 in magnitude• Carries a charge• Leaves a hit on the outer 5 detector layers once and only

once (“5hit Requirement”)

Event Selection Parameters• Cosine of thrust less than 0.5 in magnitude• Thrust value greater than or equal to 0.94

Using Zpole b-bbar events

Reconstructing non-prompt tracks with AxialBarrelTracker

• Requiring all hits to lie within /2 in phi

• Requiring all hits to have the same sign in Z

Track Reconstruction

CharacterizationFigures 1-6

Accepted Events

• Figure 1: Number of Events Passing Jet Accept Requirements (out of 1000)

• Figure 2: Number of particles found and missed by the tracking algorithm vs. hits. If plotted with “0” hits the track has purity not meeting our 75% requirement

82% found with 5 hits

MC Particles Failing To Meet 5hit Requirement

• Figure 3: MC Particles which failed to meet the 5layer requirement (but passed all other requirements) vs. Radius of Origin. 81% of these particles originate outside the first layer (200mm)

• Figure 4: The same batch of particles as fig. 3, but plotted with the respective number of hits left on the detector layers. The vast majority are 4 hit tracks

A Relationship Between Hits and Rorg

• Figure 5: Two Dimensional Histogram of the radius of origin vs. hits left on the detector. The particles in this graph were not subject to momentum or path length restrictions.

• Figure 6: The radius of origin for tracks which leave exactly 4 hits. 81% originate outside the first layer of the detector (200mm)

• *Note: The fact that the number of entries and the percentage of particles originating below 200mm in this figure is the same as the particles not passing the 5hit requirement is coincidental.

Achieving Perfect EfficiencyFigures 7-13

• Figure 7: Found and Missed Particles with an MC Particle agreement restriction in place at each layer of the tracking algorithm, and the initial set variable values

Requiring All Hits to be from the Same MC Particle

87% found with 5 hits

Small Look at Z

• Figure 8: The number of hits left on the positive z side of the detector. Two of the three missed particles change sign in Z midway through their paths.

Changing “Data Members”The following variable restrictions were adjusted in the

track-finder algorithm in the following order to allow all hits to be used

(All Dimensions in millimeters except for Chisquared)

1) Seed Hit Isolation (From 0.5 to 0)

2) Seed DCA (From 100 to 9 x 10^5)

3) Pass1 Track/Hit Sep. (From 0.5 to 9 x 10^5)

4) Pass1 Hit Isolation (From 0.5 to 0)

5) Pass2 Track/Hit Sep. (From 0.25 to 9 x 10^5)

6) Chisquared (From 10 to 1.0 x 10^20)

Variables adjusted with no effect on the output until pass1 track/hit separation was changed

• Figure 9: Found MC Particles with seedhit isolation, seed DCA, and pass1 track/hit sep. adjusted. The number found with 4hits decreased dramatically, with a small decrease in the general number of found particles.

• Figure 10: Missed MC Particles with adjusted variables up to the first pass track/hit separation. There is a mild increase here from when the initial variable settings were used.

Variables continued to be adjusted with no further effect on the output until the Chisquared restriction was abolished

• Figure 11: Found MC Particles. Nearly all MC particles are found (155/157) and all but 2 were found with 5 hits.

Another Small Look at Z

• Figure 12: Number of hits on positive Z provided by the 2 missed particles, both changed Z sign mid flight.

The Requirement that all hits be on the same sign of Z was removed and…

• Figure 13: Perfect Efficiency was reached at last

Conclusions

• Most 4 hit tracks originate outside the first layer of the detector (rather than looping, they want to be good tracks but simply get a late start in life). This seems to imply that an additional layer would greatly assist in finding these tracks.

• AxialBarrelTracker (with phi-restriction and no Z-segmentation) is 75-80% efficient for finding 5hit tracks. Of the inefficiency here, roughly 1/3 is due to the mixing of hits between different particles, and 2/3 due to a high Chisquared.

• The same side Z requirement currently in place in the trackfinder, while effective in eliminating fake tracks, also creates some inefficiency.