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Status of Pattern Recognition for the T-Tracker
Hans Wenzel, Hogan NguyenMarch 12th, 2011
Introduction
Hans implemented stereo hits, formed by the intersection of 2 clusters withina plane (0-35)
Basic Pattern Recognition Concept: Start with a 2D Circle Fitter, using these stereo hits.
We analyze here how well this works.
Note: We view this 2D fitter as part of the Pattern Recognition Algorithm, whose goalis to handing off good straw hits to the Kalman Fitter.
1
Outline
- Quick Review Of Basic Concepts and Previous Work(http://mu2e-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=1337)
- Z information from the 2D Fitter
- Evaluation of simple pattern recognition with Accidental Overlays
- New Tools to Help Pattern Recognition (Hans)
6 Configurations for Stereo Hits
Panels Used Plane-----------------------------------------------
0 & 1 or 3 & 4 even plane 1 & 2 or 4 & 5 even plane 2 & 3 or 5 & 0 even plane
0 & 1 or 3 & 4 odd plane 1 & 2 or 4 & 5 odd plane 2 & 3 or 5 & 0 odd plane
3
4
systematicshift in position
strawcluster
strawcluster
electron
Example:
polar angle = 72 degreesPhi angle = 90 degrees
No Shift in Y coordinate.
Systematic shift in X coordinate =
(19/2 mm)/tan(90-polar)*tan(30) = 17 mm
trueposition
Systematic Shift of Stereo Hit Position
StereoHit Position
Fit Minimizes Perpendicular Distance To Circle.
3 free parameters for a 2D circle:
X0, Y0 is the fitted center, and R is the fitted Radius Notes
NO SEARCH ALGORITHM – ALL Stereo Hits are used in the FIT
Errors Calibrated From MC(see Next Slide)
Adhoc Correction done toaccount for polar angle dependence of the StereoHit.
Can do it rigorously later
5
Radius of Stereo Hit - Radius of True Hit
Confi
gura
tion
num
ber
Errors Used in the 2D Fit. Calibrate using Monte Carlo
6
Radius Error of 2 mm Phi Error of 5 degrees(Phi not used in the fit)
Phi – True Phi
allow 1 iteration to refit excluding theworse chi2 contributor
Fit Consistency
Low ProbabilityFits due toMultiple Scattering,Interactions, andPathological ClusterShapes
7
Rejecting Low Probability EventsKeeps = 83% (NO OTHER HITS)
Delta phi = angle of stereo hit with respect to first stereo hit
Period in Z = Position drift in Zfor ONE complete orbit rotation.Calculated ASSUMING p=105 MeVHypothesis
Z Period number (dimensionless) =Number of Z periods
first hit
second hit
third hit
DefinitionZ information from the 2D fitter
Ideal Case
DeltaPhi
Z Period Number (calculated assuming Conversion Electron Hypothesis)
All Hits from Conversion Events Lie on theCurve, Independent of Polar Angle of Conversion Electron
Z period Number (dimensionless)
Delta Phi (degrees)
Monte Carlo Truth Positions Used& Selected P > 103 MeV
Radiated ConversionElectrons cause off-diagonal points
Rotation Angle (Phi) versus Z
2000generatedconversionevents
Z period Number (dimensionless)
Delta Phi (degrees)
Rotation Angle (Phi) versus Z Reconstructed Stereo Hits Used
Errorsin definingthe First Hit(1% effect)
2000 generatedconversion events
Overlay of Accidental Hits onto Conversion Events
Process Rate Per Microbunch Number of Clusters
Pure Conversion -- 23
Ejected Protons 5628 16 (After ADC cut)
Decay In Orbit* 36K 4
Pion Capture 75 7 Cosmics small ~ 0
Electronics Noise Study Not Done TBD
* Generated only DIO with E>60 MeV to save computing time
Thanks to: Gianni, Bob, Craig for Rates
100 Pure Conversion Electron Events ( cos(polar) = 0.3)
deltaPhi
Z Period NumberStereo Hits in Circle-Centered Coordinates
Fit Cut Eff = 83%
100 Conversion Electron Events Overlayed with Pion Capture
deltaPhi
Z Period NumberStereo Hits in Circle-Centered Coordinates
Pion CaptureAdds ~ 7 ClustersPer Event
Fit Cut Eff = 66 %
100 Conversion Electron Events Overlayed with DIO Events
deltaPhi
Z Period NumberStereo Hits in Circle-Centered Coordinates
DIO Adds about 4 ClustersPer Event
Fit Cut Eff =70 %
ADC is Critical for Removing Proton Ejection Events
Conversion Events Proton Ejection Events
ADC < 6 KeV
100 Conversion Electron Events Overlayed with Proton Ejection Events
Proton Ejection Eventsadd 16 more clustersper event (after ADC cut)
Fit Cut Eff = 10 %
Stereo Hits in Circle-Centered Coordinates Z Period Number
What Next
- The ADC cut is critical. It is doing the lion’s share of removing bad hits.
- Simple 2D fitter with NO search algorithm fails with accidentals
- Need to Beef up the 2D fitter with a search algorithm
- Hans will discuss other tools.