Measurement of the magnetic field direction

We study the deviation of an electrons in the TPC local coordinate system in order to measure the direction of STAR magnetic field.
Local c.s. is shown below:

where z local - drift distance and it changes it's sign from the East (+1) to the West (-1).
Local z axis conicide with Tpc Z axis and flip it's sign to the West direction due to the
dirft direction.

We have measured the deviation of the electrons in that system in x and y directions
in a cosmic data, where no tracks were in TPC (no collisions) and we have switched off
all the corrections.

We rejected very short tracks (<=20 cm) and excluded Sector7Row1, Sector13Row36, Sector17Row43 (looks like only one pad)
from the analysis because of the noisy padrows.

Short tracks with length <=20 cm correspond to the garbage that shown on the left bottom plot.
 
Then we have built deviation in x (tX) and y (tY) directions for the Reversed Full Field and for the Full Field
versus sector# :

Here tX corresponds to the and tY corresponds to components
of the magnetic field. Magnitudes of the tX and tY are measured in radians.

On the left side the strong deviations from the 0 may be explained by  short on the West.
The tX on the East where short is absent one can see the positive shift that
gives which means that the electron always has additional component on 
direction.

The result of applying the short correction (ExB,OShortR) is shown below.

The result of applying the short and magnetic field map correction (ExB,OShortR,OBmap) is shown below.

The data obtained for Monte Carlo simulations (a pol0 fit value shows the shift):

1) One dimentional cluster finder:

2) Two-dementional cluster finder: