[Frost] phi offset

[Eugene Pasyuk]

We know that the beam was off the CLAS center in g9a and g9b. I suspect that beam offset might not properly accounted for in tracking. Could it be a problem in translation from sector coordinates to CLAS coordinates? May be instead of translating to CLAS coordinates we need to translate to "beam" coordinates? 

-Eugene

----- Original Message -----
> From: "Michael Dugger" <dugger at jlab.org>
> To: "frost FROST" <frost at jlab.org>
> Sent: Friday, July 5, 2013 3:20:49 PM
> Subject: [Frost] phi offset
> 
> 
> 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
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