[b1_ana] summary of issues

[Dustin Keller]

Hi,
I've added some comments below,

On Sun, 9 Jun 2013, Karl Slifer wrote:

> 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?).
>

This was the point of the two plots at the end of the note, they
showed exactly that.  We could nearly cut the drift and relative
uncertainty in half using techniques we already have good understanding
of.  At the moment we put the optimistic projection back to 30% rather 
than 40% polarization.


>
> 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?
>
>

It might be a good idea just to educated them a little about this without
being argumentative.  There really is no possible change in drift due
to depolarization by draining the helium temporarily.  My best guess
is that they miss-interpreted thinking we would run the beam on it
without helium.  Not the case at all.


> 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.
>
>

Actually the value used in the note is twice what was used in the 
proposal.  The 6x10^-4 had not yet be corrected for effective pol. Its 
twice as big because I used larger numbers to emphasize from each
drift that they were concerned with that even without the upgrades we are
still in business using previous experiments to estimate.  These estimate
are all under the assumption of careful control and monitoring.  The up 
grade just help even more.


> 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.
>
>

A couple of aspects about this confuse/concern me.  First if its no 
detriment then can we just ask for $ for a stronger magnet.  Does needing 
a stronger magnet diminish the likelihood of approval.  Also do we
diminish the likelihood of approval by say the R&D can only happen
with approval?  Its important that they understand that there is a 
limited number of things about tensor polarization optimization that 
can be demonstrated without the use of beam in a real experiment.  I'm 
asking only because I don't understand politics and requirements.


> 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?
>

It is nice that unpolarized beam did turn out to be completely possible,
probably that the last we will hear of it though being it too convenient
just to run with polarized.


>
> 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.

There are also other corrections/accounting that can come into play around 
the target only asymmetry and such.  All issues are still near negligible 
except for issues regarding the angular dependence of HMS for range of kin.





dustin


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