1

Adventures In Calorimeter Assisted

Tracking

Chris Meyer, Tyler RiceUC Santa Cruz

October 16, 2007

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Tools

The goal is to put together a combination Track Finding Driver for the central region of the detector. This includes:

• VXD Cheating• AxialBarrelTrackFinderZ• GarfieldTrackFinder

These are run through sequentially, eliminating hits found on tracks after each step.

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VXD Cheater

We started with code written by Eric Wallace (formerly of UCSC) and modified it to cheat away not only Tracker Barrel Hits, but Vertex Barrel Hits as well.

All associated SimTrackerHits from MCParticles originating within 2 cm of the origin are removed from hit banks.

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AxialBarrel Z

Code originally written by Tim Nelson (SLAC), it takes three hit seeds from the Tracker Barrel and attaches hits to find 4 or 5 hit Tracks.

Optimized for non-prompt tracks by Tyler Rice (UCSC); Some improvements added (phi-region check…).

The code used was modified by Lori Stevens (UCSC); introduced virtual segmentation and an algorithm to check for linear z-consistency using only end-position information from z-modules.

Z-Modules are user defined, changeable in the Driver.

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GarfieldTrackFinder

Written by Dima Onoprienko (KSU), GafieldTrackFinder employs outside-in track finding, beginning with EmCal Stubs.

Finds tracks with 3, 4 or 5 hits in Barrel Detectors.

Also uses modular z information when finding possible hits to attach to track.

Changes made to Garfield:• GarfieldTracks/Hits have associated MC truth information• Virtual Z-Seg now customizable

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What’s a Good Track/Particle?

Findable MC Truth Particle:• FINAL or INTERMEDIATE State Particles• Charged• Path Length > 50 cm• Pt > 0.75 GeV• Radius Origin < 72 cm• | cos | < 0.8

Acceptable Reconstructed Track:• | cos | < 0.8• Pt > 0.75 GeV• DCA < 10 cm• Successfully Fit

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What’s a Good Track/Particle?

Good Tracks:• Purity ≥ 0.8• Associated MCParticle is findable• Passes acceptable criteria

Fake Tracks:• Purity < 0.8• Passes acceptable criteria

Ignored Tracks:• Purity ≥ 0.8• Associated MCParticle is UNfindable

*Purity is calculated strictly using Barrel Hits (Calorimeter stub excluded from calculation)

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Initial Results

5 Hit Tracks

0

20

40

60

80

100

120

140

160

180

30cm 10cm 5cm 1cm

Z Segmentation

Nu

mb

er o

f T

rack

s # MCP's

AB Found

AB Fake

GAR Found

GAR Fake

Missing

*Axial Barrel ≥ 4 hit Tracks, Garfield ≥ 3 Hit Tracks*

*Z Pole qqbar Event*

*5 Hit Tracks*

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Initial Results

Axial Barrel4 Hit Tracks

0102030405060708090

30cm 10cm 5cm 1cm

Z Segmentation

Nu

mb

er o

f T

rack

s

# MCP's

AB Found

AB Fake

Missing

*Axial Barrel ≥ 4 hit Tracks*

*Z Pole qqbar Event*

*ABTFZ 4 Hit Tracks*(Garfield Will Be Run Next)

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Initial Results

Garfield4 Hit Tracks

0

2

4

6

8

10

12

30cm 10cm 5cm 1cm

Z Segmentation

Nu

mb

er

of

Tra

ck

s

# MCP's

GAR Found

GAR Fake

Missing

*Axial Barrel ≥ 4 hit Tracks, Garfield ≥ 3 Hit Tracks*

*Z Pole qqbar Event*

*# MCPs are those left after running AxialBarrel*

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Initial Results

*Axial Barrel ≥ 4 hit Tracks, Garfield ≥ 3 Hit Tracks*

*Z Pole qqbar Event*

3 Hit Tracks

0

10

20

30

40

50

60

70

80

30cm 10cm 5cm 1cm

Z Segmentation

Nu

mb

er o

f T

rack

s

# MCP's

GAR Found

GAR Fake

Missing

VERY Low Purity for Reasonable Segmentation

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What Are We Missing?

If we change to 5 hit minimum for Axial Barrel Purity is increased, but efficiency is decreased (Tyler Rice presentation, 8/21/07).

The main concern is the inability of the calorimeter to distinguish good 3 hit tracks from fakes.

Can we reliably reconstruct tracks originating outside the second Tracker Barrel layer?

SeedExtend Algorithm, Tyler Rice, Chris Meyer

Since Barrel information is precise, make a helix from 3 hit seeds (with seeds based on Tim Nelson’s code) then check for matching calorimeter stubs (found using Dima Onoprienko’s NN Cluster Driver and EmCalStub Driver).

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Stub Matching

*Muon 1-50 GeV Events*

XY Miss Distance between Seed and Stub at Calorimeter Face

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Stub Matching

*Muon 1-50 GeV Events*

Phi Difference between Seed and Stub at Calorimeter Face

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Stub Matching

*Muon 1-50 GeV Events*

Curvature Ratio of Seed and Stub

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Cuts on Matching

ZPole sidaug05 cuts for SeedExtender

Seeds:• Phi Separation < 300 milliradians (for consecutive layers)

Helix – Stub Matching:• Base Difference < 2 mm• Phi Difference < 100 milliradians• Kappa Ratio ( (seed - stub)/ seed ) < 10

Note: All values are absolute values

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Approach

Loop through list of stubs looking for possible seeds to attach.

Calorimeter Stubs:• Refit stub to get better helix (base position, base phi, kappa)• Use all CalorimeterHits, give more weight to closest two,

farthest two, and middle two

Tracking Seeds:• Only look at outer 3 tracking layers• Require max phi-separation between any two hits of 300

miliradians

If multiple matches are found, seed with smallest phi difference from stub is used.

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Seed Extender

20 total Findable 3 Hit tracks.

Binned by Radius from Origin (mm)

Radius of Origin

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Seed Extender

12 Found 3 Hit tracks.

Binned by Purity*

Include stub as 4th hit in purity calculation

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Seed Extender

2 Found 4 Hit tracks.

Binned by Purity (5th Hit from Calorimeter assumed to be pure)

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Seed Extender

4 Fake 3 Hit Tracks.

Binned by pt (GeV)

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Conclusions

ABTFZ and Garfield• Efficient and Pure for 4 and 5 Hit Tracks

Can’t find 3 Hit Tracks

Developed SeedExtend for 3 hit Tracks• On Z-Pole events we get 60% efficiency for 3 Hit Tracks• On Z-Pole events we get 70% purity for 3 Hit Tracks

This can be optimized further by changing cuts, but the optimization will depend on the physics signatures (isolated signature vs. dense jet)

Plan to look at meta-stable SUSY signature; consulted with Jonathan Feng (UC Irvine)

With this in mind Chris Betancourt (UCSC) is looking into ISAJET generation with Jonathan’s guidance.