Email from Dave:

From mack@jlab.org Fri Sep 17 11:11:43 2004
Date: Fri, 10 Sep 2004 16:34:38 -0400 (EDT)
From: Dave Mack 
To: Roger D. Carlini 
Cc: finn@physics.wm.edu, 'Neven Simicevic' ,
     'Jim Birchall' ,
     'Juliette Mammei' , 'Klaus Grimm' ,
     armd@jlab.org, 'Mark Pitt' , 'Allena Opper' ,
     'Greg Smith' , 'Norman Morgan' ,
     'Mike Finn' , 'Yongguang Liang' ,
     'Shelley Page' ,
     'Tony Forest' 
Subject: Re: Qweak- Collimator Working Group


	Roger,


	Neven's detector simulations made it clear that one could only
operate at counting statistics in two limits: with a fraction of a
radiation length (say a Cerenkov detector) or many radiation lengths (say
a calorimeter). In between, shower fluctuations add significant amounts of
noise. The first SLAC experiment by Prescott et al used both detectors
successfully if you look at the nice figure in their paper.

	I have long been a fan of building both a Cerenkov and a
calorimeter detector, stated the pros and cons of adding a calorimeter to
our scope in March 2002 (attached), and remember then ducking a hail of
rotten vegetables which was the collaboration's response. Given our
investment to date in understanding the Cerenkov option (wrt beam tests,
simulations, prototyping, researching rad-hardness, etc), I wouldn't
consider converting our primary detector to a calorimeter at this point.  
Pursuing the calorimetry option would require a complete reassessment of
the backgrounds, sensitivities, radiation damage, choice of materials and
glues, etc. It's still a good idea, but we're missing the group to take on
responsibility for design and construction of a separate calorimeter.

	Unfortunately, compared to what we might have thought in March
2002, our ability to widen our scope has not improved: 1) we have even
less money (and we can't get any more from DOE sources), 2) and most of
the collaboration manpower is now very heavily committed. I would be happy
to accept a calorimeter group inside WBS1, assuming some strong outside
group could join and get non-DOE funds to pay for it.

	regards,

	Dave

Dave's attachment:


temp.ps