Date: Tue, 07 Sep 2004 10:47:57 -0400
From: Roger D. Carlini 
To: Allena Opper , mack@jlab.org, neven@phys.latech.edu,
     pitt@vt.edu, tony@phys.latech.edu, grimm@jlab.org, finn@jlab.org,
     jmammei@vt.edu, nmorgan@vt.edu, smithg@jlab.org,
     birchall@physics.umanitoba.ca, armd@jlab.org, yl0094a@jlab.org
Cc: smithg@jlab.org
Subject: Qweak working group - Comments


Hi Folks:

My understanding of where we stand is the following:

1)  We have re-established a base design which will allow us to achieve a 4%
qweak measurement in about 2200 hours + 
comissioning time (at 85% polarization) even after a deduct for internal
radiative effects. There are infact several 
solutions to choose from at various are Q**2 and Theta acceptances which fit on

a slightly longer than 2 meter bar.

2)  Also, there seems to be more agressive solutions which would reduce the
running time significantly, but at a price:

       a)  Operating at a higher average Q**2 --> potentially requiring a
better determination of the residual helicity 
correlated hadronic ff's.

            and/or

       b)  Opening up Theta and Phi to such an extent that the detector
concept/geometry must be radically altered.

3)  Mike Finn has also observed that if the target were moved upstream we could
force the average Q**2 significanly 
lower. I believe this will work but at the loss of solid ange and asymmetry,
but its worth a Monte-Carlo run. This might 
be a nice "hold in reserve" along with the option to reduce the beam energy as
a means of "tweaking" the average Q**2 at 
run time if we conclude that we need to suppress the residual helicity
correlated hadronic ff's further. My bet is that 
we won't need to do this for a 4% measurement.

Bottom line:  We first need to confirm that we have not missed any "easy"
improvements in running time and make a call 
between approaches 1 and 2 above. We might consider going with the conservative
approach 1 for the jeopardy proposal and 
keep working on option 2 quietly for the 4% (or possibly better) production
run. If after analysis we believe that the 
hadronic ff's contributions can be kept small then the optimization criteria
may be very different and the experiment's 
ultimate goal will likely change.

Best Regards

Roger