Minutes of 9/23/04 Teleconference:
Date: Mon, 27 Sep 2004 10:53:27 -0400 (EDT)
From: Mark Pitt
To: Roger Carlini
Cc: Jim Birchall , Juliette Mammei ,
Klaus Grimm , Neven Simicevic ,
Greg Smith , Allena Opper ,
Tony Forest , Norman Morgan ,
Mike Finn , David Armstrong ,
Yongguang Liang , Shelley Page ,
Dave Mack , Richard Jones
Subject: Qweak PCWG - next meeting and minuts of last meeting
Hi folks,
We agreed that we would meet again this coming Thursday
September 30 at 4 - 5:30 PM for the Qweak primary collimator
working group. I will send out the phone details and an
agenda the day before the meeting.
Below are minutes of the last meeting including ACTION items.
Please send corrections to this list if I misrepresented
anything.
Minutes of Thursday Sept. 23 Qweak Primary Collimator Working
Group
1. Inelastic/elastic ratios and FOMs have been computed (by
Jim, Neven, and Juliette) for both the upstream and downstream
collimators. Here is a summary of the results:
Scenario Rate (MHz) Q2 FOM inelastic/elastic
Neven downstream 734 .0239 .418 .002%
Jim 10-8-22 594 .0317 .596 .31%
Jim 9-8-22 543 .0293 .467 .09%
Jim 8-8-22 468 .0267 .335 .01%
where FOM is defined as rate * (Q2)**2.
The rates for Neven's collimator were done with radiative effects
turned on. For Jim's rates and FOM I mulitiplied his rate and FOM
by 0.76 to approximately account for the hit we take for radiative
effects. Roughly, we need a FOM of about .630 for a 2200 hour
experiment that achieves the proposal statistical error.
Currently, only the Jim 10-8-22 collimator is close to that, but it
has an unacceptably high inelastic/elastic ratio. It is not fair
to compare the inelastic/elastic ratio for "Neven downstream" versus
"Jim 10-8-22" because they represent different theta ranges. Jim's
"extreme rays" go from 6 to 14.5 degrees, while Neven's extreme rays
only cover 6 to 11 degrees.
ACTION items:
a) Jim will compute the FOM, Q2, and rate entries in the above table
using Richard Jone's radiative corrections routine.
b) Juliette will modifiy Neven's downstream collimator so its
extreme rays are the same as Jim's 10-8-22. Then she will recompute
the entries in the above table. Mike says that his calculations indicate
that, for a given set of "extreme theta rays", the FOM improves as you
move the collimator downstream making the target more pointlike. This
sounds correct, but everybody agreed that we would like to see it directly
from the simulation.
2. Neven's downstream collimator: Greg pointed out (based on the geometry
numbers that Juliette posted for Neven's collimator) that it appeared the
downstream half of his collimator was defining (rather than the upstream
half). I looked at Neven's original email, and that is certainly not
what he intended.
ACTION items: Juliette will modify the downstream collimator so the upstream
half defines the acceptance and the downstream half is only cleanup.
3. Prescription for tolerable inelastic/elastic ratio:
We agreed to the following prescription for what sort of inelastic/elastic
ratio that we can accept. This is the same prescription we have been
using all along:
Since the scale of the inelastic asymmetry is roughly 10 times higher
than the elastic (just 4sin2(thetaw) vs. 1-4sin2(thetaw)) we will
multiply the inelastic/elastic ratio by 10 to get the upper limit
contribution to the asymmetry. We will require that number to be < 0.2%.
By that prescription, only the "Neven dowsntream" and Jim "8-8-22"
collimators in the above table qualify, but their FOM is too low.
4. Background from the "slit edges" of Neven's downstream collimator:
As Roger has pointed out, we do need to check that a downstream
collimator will not have "hot" edges that will be line-of-sight viewable
by our main detectors.
ACTION item: Youngguang will start to make tomographic plots of backgrounds
for the "Neven downstream" collimator.
5. Other ideas:
a) Sculpted collimator: Roger has proposed considering a "sculpted"
collimator that would have theta accepatance that varies as a function
of phi. The basic idea is to throw out large theta, large phi rays where
our inelastic/elastic separation is bad.
ACTION item: Juliette will start to investigate this for the "Neven
downstream" collimator.
b) Roger asked if we should consider a shorter target. The idea would
be that we could reduce some of our radiative losses. Greg pointed
out that this needs to be estimated carefully because our fractional
errors from end window contributions would become more important.
Nobody volunteered to look into this yet.
6. Geometry stuff: We agreed to the following geometry issues. This
is only for now, so that we are all using the same geometry:
Scattering chamber window: 10 mil aluminum
Target side walls: 20 mil Be
Target "end windows: 10 mil Be
Regards,
Mark
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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
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