From jimb@mts.net Thu Sep  9 07:40:52 2004
Date: Wed, 08 Sep 2004 21:32:09 -0500
From: Jim Birchall 
To: carlini@jlab.org
Cc: 'Mike Finn' , finn@physics.wm.edu, armd@jlab.org,
     'Neven Simicevic' , 'Mark Pitt' ,
     'Allena Opper' , 'Juliette Mammei' ,
     'Dave Mack' , 'Klaus Grimm' ,
     'Shelley Page' ,
     'Tony Forest' , 'Greg Smith' ,
     'Norman Morgan' , 'Yongguang Liang' 
Subject: Re: Qweak working group - next meeting

Yes, I ran a large number of cases, rotating the upstream end of the 
coils out and in radially and moving the magnet relative to the 
collimator, but didn't find any clear advantage. I'm sure it's possible 
to decrease the azimuthal defocusing, but at the cost of radial 
focusing. I'll check my log books in the morning.

Jim

On 8 Sep 2004, at 8:46 pm, Roger Carlini wrote:

> Hi Mike:
>
> With regards to your second point. Jim did those cases last year when 
> he was at JLab and I don't believe there was a significant inprovement 
> in focusing by rotating the coils outward. Jim could you please cross 
> check my memory if you have your log books handy.
>
> Also, Jim ran your case of moving the target upstream, indeed the 
> average Q**2 drops, but the FOM decreases: Jim's recent email to me:
>
> "A quick result using the 10-8-22 collimator and moving the target 50 
> cm upstream (and widening the front of the collimator so it's out of 
> the way). The rate above 1000 MeV is 1465 MHz, Q2 = 0.01662, figure of 
> merit = 0.405. The original 10-8-22 collimator had 782 MHz, Q2 = 
> 0.0317, FOM = 0.784."
>
> This option might still prove attractive if acceptance could be 
> increased by going to an aggressive 10-8-28 phi acceptance 
> (overlapping images maybe) if we have to live with a large "B" term. 
> Our beam related systematics will be larger as the average asymmetry 
> will decrease and our sensitivities to angle/position motion will also 
> increase somewhat.
>
> Best Regards
>
> Roger
>
>