[G8b_run] g8 Meeting tomorrow

[Eugene Pasyuk]

Ok.

On Wed, 2009-08-12 at 11:10 +0100, Ken Livingston wrote:
> 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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> >   
> 
>