[g13] linear pol

[nivanov at jlab.org]

Hi Ken and other g13 Users,

I have 2 questions about the available calculations of the photon linear
polarization for g13.

1. Presently there are 2 sets of quick and rough estimates of the mean 
polarization. The first set is presented in the Daria's message by 15 July
2009. The second one is given in Neil's polarization tables at
http://nuclear.gla.ac.uk/~kl/g13/poltables.tgz
(see the file meanpol.txt in cbremROOT directory).
Unfortunately, there is a difference (up to 15%) in the results presented
in these sources. So, my first question is: What predictions for the
polarization are more reliable? What numbers we should use in our
analyses?

2. In Neil's polarization tables (pol_tables_*.dat), the ANB predictions
for the polarization for different coherent edges are presented. However,
to have reliable predictions for a real experiment we need also the
coherent edges distributions for this experiment. The second question is:
How and where we can get the coherent edges distributions for g13b?

Unfortunately, Ken, your explanations of this topic given at
http://www.jlab.org/ccc/mail_archives/EXPERIMENTS/g13/CURRENT/msg01026.html
are not quite clear for me:

> For the files you analyse for, say 1300MeV, make histograms of the
> distribution of coherent edge positions (which you get every 2s)
> for para and perp.

> Also, make a photon energy distribution of para and perp photon energy
> for your good tagger hits for the events which make it through your
> cuts.

Could you explain in more detail what the g13 users should do to get the
coherent edges distributions?

Thank you very much,
Nickolay






> Hi Yordanka,
> Had a talk about the linear pol with Neil. The current tables are based
on a representative sample from each run period, so we don't have a
distribution for each run. I'll produce one this week, but need to run a
local farm job to do so.
>
> Cheers,
> Ken
>
>
> --
> =======================================================
> 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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