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.