Hough Transform on SZ Plane

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)

(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

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)

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

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

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

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

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)

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

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