[b1_ana] summary of issues

[Karl Slifer]

Hi all,

Below is a summary of the issues identified by the TAC, iTac, PAC readers,
or within the collaboration. None of this is new, and Dustin has also
created an excellent technote discussing many of these issues, but here
I've attempted to discriminate between major issues that we must focus on,
and secondary issues that either are not as important or that have been
resolved already. I'd like to use this strategy of prioritizing our
responses to the PAC reader questions (with concrete backup reference to
Dustin and Ellie's tech notes), so I'd appreciate feedback.

-Karl




Major Issues
-----------------

I) The significance and interpretation of our measurement.

 Status: The iTAC states it is unlikely we can discriminate between the
curves in Fig. 7.  They suggest that we need to half the error bars and
increase the number of measured points.

Proposed Action:  The iTAC missed the point that *any* non-zero measurement
of b1 at any of our x points would unambiguously confirm its
non-conventional nature.  We can also cite the Theory TAC which states that
"*With very little experimental information currently available, any new
data on b1 would be clearly welcome*."  If we wanted to directly respond to
the iTAC's critique, we can also possibly put together an estimate of what
it would take to half the error bar and increase the points (Pzz=40%,50%?,
xx additional days of beam?).


II) Stability of the target thickness, packing fraction, and dilution factor

 Status : iTac is concerned about annealing, and draining helium to
depolarize.

 Action : We need to make clear that each pol/unpol cyle is an independent
measurement, and annealing does not impact each "slug". We need to make
explicitly clear the specific sequencing and how each slug is combined to
get the final results.  The most efficient way to depolarize is to drain
helium, and we have convincing data to defend the use of this method, but I
think it is probably best to just agree to depolarize the target with
microwaves or AFP (we already say we'll do this in the proposal pg 30). I
don't think it is productive to argue about how safe draining Helium is
when we have practical alternatives.   Dustin talks about target thickness
in the note. Luminosity can be monitored with lumi or with the unpolarized
yield but to what precision?


III) Systematic errors (particularly from drift)

Status: TAC says our systematic analysis is "on point" but lists several
systematics it is concerned about.  TAC also explicitly states that it is
possible to handle these with ugrades and sufficient committement from our
collab.  Most of the questions from our PAC readers are about systematics.

Action:  Make list of the upgrades (temp stabilized bpm, new faraday cup,
lumi) which Dave suggested (and listed himself as contact).  Ask Dave to
provide whatever details we can get before the PAC so we can show a few
slides on the new hardware.  In the collab, identify who will take
leadership on this,  and point out that having a team work on this is
similar to how we handled things in g2p (which also had heavy target
commitment, but still had independent groups working on several other
projects).   Reference Dustin's detailed note to assess value of the pieces
not explicitly discussed in the proposal.  Address the new comments from
the PAC readers in the note.

Comment: I think in Dustin's note we should summarize the new value
(6*10^-4) in the abstract and explain why this is less than Eq 30 of the
proposal (further studies and input from the TAC + sqrt(N) from multiple
cycles).  An additional column should be added to Table 1 of Dustin's note
with the factor sqrt(N) included.  Also a big point that should be
emphasized in the abstract is Dustin's conclusion (from Eq 1) that dAzz
reduces by the same factor that we can improve Pzz. Finally, the abstract
should note that we have already started thinking about how to extract Pzz
from the NMR line shape.  If Dustin doesn't object, I would like to make
these structural changes to the document before we send to the readers.


Secondary Issues
-------------------------

1)Value of Pzz without hole burning.  (This could be considered a major
issue, but I feel pretty confident we can defend large values of Pzz)

Status : We claim Pzz=20%, Tac claims 12%.  Strictly speaking the TAC is
right and 12% could be considered the "safe" value.  Our 20% value depends
on some incremental improvements to the existing target, but we stated as
much in the proposal.  In particular, we were assuming using a larger
magnetic field.  We also have some refs in the literature that support the
20% value, but none of them are quite exactly the same as the proposed
conditions.  For example, Z. Phys. C -Particles and Fields 49, 175-185
(1991) ran a very similar target in an electron beam with <Pzz>=22.5%, but
with a 3He/4He fridge.  On the other hand, TAC/iTAC are very confident that
hole-burning will produce large Pzz, and we have strong support from JLab
target group that this will work also.

Proposed Action: We could defend our 20% value with the citations from the
literature along with a display of how the vector polarization improves
with B, and a list of refs with Pzz ~ 20%, but this seems
counter-productive to waste much time arguing for the lower value of Pzz,
when the TAC/iTac seem to be pushing us to Pzz=30%.  We do need to prepare
some slides with the description of the basic process of hole burning and
the evidence indicating it should be successful.  We also have to make
clear that there will be no improvement in Pzz without an approved
experiment to justify the R&D.


2)Parity violating Asymmetries

 Status: This issue was noted by the TAC, but they also suggested that they
will be small and manageable.  This conclusion was confirmed by Wally.
 Oscar investigated it in detail, and the results are summarized in
technote by Ellie/Oscar.

Action: The TAC already says it will be manageable.  We should cite the
technote as supporting document and have our study results ready as backup
slides.

3)Polarized vs Unpolarized beam

Status : Unpolarized beam simplifies the analysis, but we are fine with
polarized beam as long as we rely on feedback from one of the other halls
which are running at larger current. Also have to take some special care,
to cut around beam trips for example, but using polarized beam for
unpolarized experiments has been done successfully several times.

Action: We need a few plots from Transversity to have as back up, but the
TAC/iTAC states its not a problem so no action is needed.  JP pointed out
that parity feedback will allow control of the (non)polarization of the
beam to the 10^-5 level. Do we have a plot to show this?


4)Alignment of vector polarization along beamline vs. q-vector.

 Status:  We've investigated this and found it to be negligible (at worst,
a small multiplicative factor to Pzz at largest x point ).

 Action: This was never even raised by the TAC/iTAC.  We can include as
backup slides.




---
Karl J. Slifer
Assistant Professor
University of New Hampshire
Telephone : 603-722-0695
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