[Eg1_run] Eg1b Exclusive Pion Analysis

[bosted at jlab.org]

Dear Eg1b collaborators,
   I would like to tell you that I have started to analyze
longitudinal spin asymmetries (A_LL, A_UL, and A_LU) in exclusive
pi+, pi0, eta, and pi- electro-production from all four beam
energies of the Eg1b experiment, covering all available values
of W and Q2. My motivation is to have a comprehensive set of
data to include in a global fit to world data. This is needed
because none of the available fits such as MAID and SAID describe
cross sections and asymmetries well, especially for Q2>1 and
W>1.7 GeV. I need an improved fit so that we can have reliable
radiative corrections to SIDIS as measured in eg1-dvcs. The
lower beam energies of eg1b are extremely useful, as most
of the exclusive events that radiate into SIDIS bins come from
beam energies of 2 to 5 GeV.
   Although it was extremely challenging, I managed to get the
dst reading code working on the "ifarm" machines. I then
modified my dst-reading code to make new skim files for the exclusive
channels. Making the skim files only took one week, with the
much faster computer available today than 14 years ago. The skim
files that I had made some years ago did not include all of the
topologies that I wish to analyze.
   I then adjusted the various exclusivity cuts for the various
topologies to optimize the signal to noise.
   I then made fits to the ratios of carbon/NX3. I use those
fits to get the dilution factor.
   I then get the three beam symmetries for each configuration
(beam energy, torus polarity) and topology. For each pion flavor,
I have two topologies: one in which all final state particles
are detected (including neutron in the n pi+ final state), and one
in which one particle is missing.
   I then combine the two topologies for each flavor, and the
in-bending and out-bending configurations for each beam energy.
   The results are stored in fine kinematic bins, to avoid large
bin-centering corrections.
   I've written most of the corresponding analysis note. I expect
I will have the first draft ready by the end of the week.
   Please let me know if you are interested in participating in
this analysis. Please accept my apologies for not announcing
this project sooner. Honestly, I didn't really think I would
be able to get the dst-reader working, and six weeks ago just
about gave up. After that, it has been relatively easy to make
progress, because I was able to make relatively small modifications
to my eg1-dvcs code.
   In particular, I would love help in comparing my results with
the pi+ results of Josh (4.2 GeV) , pi- results of Sharon (2.5 and 4.2
GeV), and pi0 results of Angela (1.6 GeV in-bending). The latter
are the only exclusive results actually published so far from
eg1b, in spite of the experiment having run 14 years ago.
   Another area that always provokes a lot of discussion is the
treatment of systematic errors. I am happy to consider suggestions.
   Yours, Peter