1. Hough Transform on SZ Plane

2. Stereo hit position calculation (review)
Use circle track & driftdist calculate (z,s) on stereo wire
Z: z of hit on stereo wire
S: flight length of the hit on stereo wire
For each hit , two assumption for (left & right) ambig ->two (z,s)
Z(cm)
Truth hit
Different ambig(left ,right) by calculation
Calculated , use truth ambig
S(cm)

3. (sz)Hough transform By Hough ,transform (s,z) plane to (tanl,z0) plane
(k,b) of each two points in (s,z) ->fill in (z0,tanl) space
Z(cm)
z0(cm)
S(cm)
tanl
Focused area means most possible parameter of the track

4. Improve the method on z-s plane Method
event sample :
MC pi- , 50MeV<|pt|<120MeV
No decay no delta e
Drop multi turn tracks ( flight length of hit from second track > length of circle)
Use all signal stereo hits of first half circle track
Improve the method on z-s plane
Method
Step 1: calculate every hit position (z & flight length) on stereo wire with circle information
Step 2: Hough transform on (tanl , z0) space
Step 3: confirm (tanl,z0) of the track parameters on (tanl,z0) space (simple peak finding method)

5. Some details( s,z calculation)
in (s,z) calculation , not accurate result ,
especially when layer>8
Angle of track and stereo wire?
Many wire on same layer? cm
Begin has outer stereo layer
MeV
z:_delta: (calculated z of truth ambig) – ztruth
Error of calculated z is much bigger in outer chamber

6. Improvement of (sz)Hough transform
Calculate every line of points in same super layers
Each two points add (0,0) to fit a straight line
Chisquare cut && z0cut && tanlcut ->candidate line
Fill candidate line in (tanl,z0) space
Z(cm) X
Peak method:
The (tanl,z) of the peak most possible means the track par
The highest bin ->the peak
If more than one highest bin , average of them
S(cm)
Tanl ,z0 cut: |tan|<2.25 (costa ~0.93) |z0|<10cm
Chisquare cut: chi2<1

7. Preliminary result Tanl-tanlTruth: Z0-z0Truth No background
add background
No background
add background
(cm)
(cm)

8. Ideal circumstance
If we use right ambig of each stereo hits , by least square fit
Z(cm)
No background
(cm)
S(cm)
Sigma :0.48
Resolution of tanl by (sz)Hough transform are close to the ideal circumstance

9. What could be better? need optimized for some method or parameters
By (sz)Hough transform as first step , noise hits & hits in second circle may be reduced by using preliminary parameter
Come from 2nd turn
Z(cm)
Wrong s, reduce a circle length
Should be here
S(cm)

10. What could be better? From panda
We can try not to use (s,z) calculation method
From panda

11. Genfit status Now can run for reconstructed track
For pi- lowPt event sample , reach ~90% fitting success ,but may be some error in the progrem