[Frost] phi offset

[Michael Dugger]

Hi,

>From CLAS-Note 2003-017 (Mike William's kinematic fitting CLAS-Note), the 
lambda resolution of CLAS from the TBER bank (using data with  0.5*B_max) 
is about 2.5 mrad. The value of lambda used in the kinematic fitter was 
1.5 times as that given in TBER.

This gives us a resolution of about 0.21 degrees for lambda. Priya's pull 
distributions for lambda of the proton (momentum < 1.0 GeV) have the pull 
maxing out at about 0.5 for angles near -90 degrees.

If I take the standard deviation for lambda to be 0.21 degrees and assume 
a transverse path-length of 1 meter, I can get the same sort of results as 
Priya if the coordinate system of CLAS was displaced from the "true" 
coordinate system by about 1.8 mm in the x-direction.

It is starting to look like the lambda pulls might be explainable by 
simply shifting the reaction vertex by a small amount.

Another way of looking at this, is that our systematic error in phi is 
about 0.1 degrees.

Take care,
Michael