[G8b_run] g8 Meeting tomorrow

[Ken Livingston]

Hi All,

I think we should have a brief meeting tomorrow to discuss:
a. How this tagger sag issue impacts on the momentum corrections and the 
polarizations tables
b. Updates on any other g8 analysis.

Please circulate any links you want to refer to (other than those below).

Can you initiate that call at the ususal time Eugene?

That's at 12.00 Jlab time. A time limit of 1 hour.

Cheers,
Ken

Michael Dugger wrote:
> Dear g8b collaborators,
>
> Stuart showed an energy dependence in the photon energy correction (for 
> g8b data) that was not a simple multiplicative factor. I decided to verify 
> Stuart's results. I found that there is an energy dependence in the photon 
> energy correction that is not a simple multiplicative factor. It appears 
> that the tagger sag correction applied to g8b data was not sufficient.
>
> The method I had been using previously (massX^2 vs. incident photon 
> energy) can not be used to determine an energy correction that is 
> different from a common multiplicative factor. Therefore, I am now using 
> an iterative routine that capitalizes on the overdetermined reaction
> gamma p -> p pi+ pi- (as is standard in this type of study). This 
> iterative routine has been successfully tested against the known energy 
> correction obtained by the CMU group for the g1c data set.
>
> The g1c CMU energy correction plot (figure 9 on page 12):
> http://www1.jlab.org/ul/Physics/Hall-B/clas/public/2004-017.pdf
>
> compares well to the ASU iterative routine
> http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/g1cEgCorr.gif
>
> The CMU energy correction has one free parameter. This parameter is an 
> offset to the fractional photon energy (E_gamma/E_e). For g8b data, in 
> addition to the standard CMU energy correction, I have included a term 
> that is a simple multiplicative factor:
> energy_correction -> CMU_correction + E_gamma*multiplicative_factor
>
> The result of this 2 parameter fit can be found at
> http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/g8bEgCorr.gif
>
> The three bump structure of the tagger sag is clearly seen.
>
> The fit results:
> multiplicative factor = -0.00351(6)
> offset = 0.00134(3)
>
> The function is very simple and a FORTRAN version of the g8b photon 
> energy correction can be found at
> http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/cmuErgCor.f
>
> I have decided not to produce a stack of slides fully describing the steps 
> taken to obtain the results shown in this email. Instead, I will write a 
> CLAS note that can be easily referenced from analysis notes. I hope to 
> have the note completed in the next week or two.
>
> Sincerely,
> Michael
>
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>   


-- 
=======================================================
Ken Livingston          

Dept. of Physics & Astronomy,        Tel: +44 141 330 6428
University of Glasgow,               Fax: +44 141 330 5889
Glasgow G12 8QQ.
Scotland. UK.
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