Email from Dave:

Date: Thu, 30 Sep 2004 12:53:03 -0400 (EDT)
From: Dave Mack 
To: Mark Pitt 
Cc: carlini@jlab.org
Subject: Re: Qweak working group - today's meeting

	Mark,
	
	I don't have any problem with the V-shape in principle. It would
actually simplify the procurement and probably save us some money, since
then I would be procuring only 100 cm long pieces which would have to be
glued. There are glues which aren't bothered by 100kRad of radiation
damage.

	If you guys get serious about this, then two things have to
happen:

1. Neven will have to simulate it and tell us how we do regarding total pe
number, uniformity, etc.

2. Such a big change would require prototype testing. That means cutting
new angles on the ends of two of our 100 cm bars, gluing them together,
checking strength and reproducibility of the glue joint, and testing with
beam or cosmics. That's all tedious but straightforward. Being realistic,
that delays me another 6 months in starting procurement of the final
quartz bars. 

	I don't see a 6 month delay as a problem if there's FOM to be
gained. If there's new physics waiting to be discovered in this
observable, after all our hard work we want to see it with 3 sigma
significance, not 2 sigma significance.

	regards,

	Dave




On Thu, 30 Sep 2004, Mark Pitt wrote:

> 
> Hi Dave,
> 
> We'll discuss your photon questions at the meeting today.
> 
> I have another question.  Are we still allowed to consider the idea of the 
> v-shaped detector?  It kind of got dropped a few weeks ago for reasons 
> I've forgotton.  But now it appears we might have a different reason for 
> needing it, which is the bad inelastic/elastic ratio for any collimator 
> that gives a reasonable figure of merit.  I haven't explored yet what 
> size/shape detector might work, but is there any reason why we shouldn't 
> continue to pursue that option?
> 
> Thanks,
> Mark
> 
> P.S. My question is also motivated by the fact that it appears the 
> sculpted collimators have to low a figure of merit.  Jim sees .48 for his 
> best attempt.  Juliette is also getting about .48 for her best downstream 
> collimator attempt; she may be able to do somewhat better.  But I haven't 
> seen solution that is up to the roughly .63 that we need.
> 
> On Thu, 30 Sep 2004, Dave Mack wrote:
> 
> > 
> > 	Mark et al,
> > 
> > 	I have to take the next generation to swim team at this time, so I
> > won't be part of today's call. 
> > 
> > 	Can someone remind me what criteria GEANT3 is using to plot the
> > secondary photons generated in the shielding/collimators? 
> > 
> > 1) we're not interested in photons which don't interact in the quartz.
> > 
> > 2) we're not interested in photons with energies below about 0.3 MeV due
> > to our Cerenkov threshold (in Babar tests, Spectrosil 2000 had 
> > negligibly small scintillation)
> > 
> > 3) we're probably not even interested in photons energies below several
> > MeV, but now I'm going out on a limb. Since the Compton angular
> > distribution and quartz stopping power are involved, only a full
> > simulation can tell us if these events have significant weight compared to
> > the 50-100 pe's generated by each elastic electrons. 
> > 
> > 	regards,
> > 
> > 	Dave
> > 
> 
> -- 
> --------------------------------
> Mark Pitt
> Department of Physics
> Virginia Tech
> Robeson Hall
> Blacksburg, VA  24061-0435
> Phone: (540) 231-3015
> Fax:   (540) 231-7511
> e-mail:  pitt@vt.edu
> --------------------------------
> 
> 
> 
>