BRAHMS Global Tracking Enhancements

K. Hagel

Review of Original Procedure

• Start with Track position and direction at T1.

• Perform Minuit fit varying p, ydir using starting values of pave=(pd2+pd3+pd4)/3, ydir of track.

2 calculated on (x,y) positions of local tracks in other tracking stations.

• Swim backwards through D1 to vertex to obtain Zvtx, θ, .

Enhancements to the code

• Vary t1X and t1Y as fit parameters

• Vary x direction as fit parameter

• Calculate 2 “correctly” using “known” σs of detectors (position and angle)– 350 m TPCx– 500 m TPCy– 200 m DCx– .5mr in θ bend plane

X difference

Y difference

Theta difference

Attempt to resolve differences in positions

• Shift detectors by difference of “where they want to be at”– t1y by -0.2cm– t2x by 0.1cm– t3y by 0.128cm

• Affects the chisq calculation

X difference (modified)

Y difference (modified)

Theta difference (modified)