[Primex2] draft text for CD-2015 proceedings

[gasparan at jlab.org]

  Dear Aron,

Thank you for your very valuable comments and useful questions. Same of
them I agree with, and some needs further discussions. Let me try to do
that as much as I can.
I think any experiment should follow theory ONLY in the beginning,
planning stage. No experimental result must follow the theory
calculations. Otherwise, there is no need to do an experiment, and all our
efforts for the past fifteen years are worthless in that case.  As a
matter of fact, the opposite is true: in the fundamental experiment
(perhaps in any experiment) one needs to   implement the “blind” method up
to the very end result. We had started with that but, did not continue. I
am sure, we all agree with this general approach.  On this way, we already
decided to do for the PrimEx-II result: both groups results, starting from
the event yields, cross sections, fits and final numbers will be requested
to have an open cross check before including any of them in the final
average.

Once we decided to show the current preliminary PrimEx-II result, then it
has to be show in Figure #6 with its 1.7% uncertainty. Then, anybody can
take 4.5%/1.7% = 2.65 ratio and get the same thing as we need to say
ourselves about our result. To me, there is nothing to hide here. After
all it is a Preliminary result as we are stating it in all places. I agree
with your suggested sentence, which is basically the same only without
mentioning this number. I think that it will be better to hear opinions
from other PrimEx-II people before we change it.

About the NLO as the only currently accepted prediction, and there is no
LO prediction. This takes us as far as ten years back. As much as know,
all we are talking here is the perturbation theory in quantum physics
therefore, it has LO, NLO, NNLO, 
  and more. We have to accept all of
published results pay respect to them.  After all, the LO is a fundamental
result from the chiral axial anomaly (with massless quarks only).

About QCD based sum rule result: this note is a short proceeding, not a
review and therefore we just mentioning it and showing the reference. By
the way, we can not ignore a work from a peer-reviewed journal, not to
talk about an author like Ioffe himself.

I will include the suggested review paper in the text, I agree on that
also (I am close to the 10 page limit already).

Thanks again,
Ashot


> Dear Ashot,
>         I think that the presentation of the PrimEx2 results as
> preliminary is a good idea as well as the inclusion of the fact
> that a second analysis is coming soon. I would suggest that the
> discussion about the preliminary results compared to the theory
> needs a little modification.
>  Within the 1.7% total uncertainty our current preliminary result is in a
> good agreement with the chiral anomaly leading order prediction. However,
> it has a certain tendency to disagree with the theory NLO corrections by
> a factor of 2.5 standard deviations (see Fig. 6)
>  This discussion gives the impression that one can choose between the LO
> and NLO results as a test of QCD. This is not the case since only the NLO
> result as it now stands is the currently accepted prediction. I would
> suggest that this conclusion be made very cautious. Here is a suggested
> revision of this paragraph:
>  The current preliminary result is lower than the NLO, QCD prediction
> within the current 1.7% accuracy. It should be taken as a PrimEx2
> progress report, not a claim of an experimental discrepancy.
>  In the long run, if indeed we significantly deviate from the NLO
> prediction, then it will be taken rather seriously by anyone in the
> larger physics community who pays attention. I'm sure that this is the
> case and the comments that I got privately from several theorists in the
> field who heard Ashot's CD15 talk strongly reinforced this opinion! This
> is the responsibility of an experiment that measures a fundamental
> quantity.
>  If the final result of PrimEx2 is a serious disagreement with the NLO
> predictions we can expect a great deal of skepticism and scrutiny, first
> inside JLab and then in the larger community. I'm not saying that we
> should change our result or not report this preliminary value, just that
> we will have to work very hard to convince ourselves that our result is
> correct, and then to be prepared to have to convince others. We should
> take this preliminary result seriously and do our best to mobilize all of
> the resources that we are able to command and be prepared to commit the
> required time to see this process through.
>  Getting back to the paper, here are a few suggested corrections:
> I would not say that the NLO corrections are small, just quote the result
> of Gamma increasing by 4.5 +\- 1.0 %.
>  I would add our review article to Rory's excellent one
> A.M.Bernstein and Barry R. Holstein, Rev. Mod. Phys. 85, 49(2013).
>  It should be pointed out that Ioffe's calculation did not take the eta'
> contribution into account. It is known that the eta' contributes ~ 1/3 of
> the 4.5% increase of Gamma. As it stands you have this contribution in
> the figure but properly do not mention it. As you know my practice is
> just not to include it in the figure. It can be mentioned in the text of
> a longer article if you want, explaining why it isn't included.
> It is nice to see all of the hard work getting reported.
> Regards,
> Aron
> Aron M. Bernstein
> Professor of Physics, Emeritus
> MIT
> Cambridge, MA 02139
> office: 26-419
> 617-253-2386
>
>
>
> On Sep 27, 2015, at 6:12 PM, gasparan at jlab.org<mailto:gasparan at jlab.org>
> wrote:
>
>   Dear PrimEx-2 collaborators,
>
>  I put together a draft text for the Chiral Dynamics 2015
> proceeding. It is in the attachment of this email.
>
> We discussed this subject in the past two weekly group meetings
> and decided to publish our PrimEx-II results as a "Preliminary".
> This text is following our decision.
>
> Please take a look and let me know if you have any suggestion or
> corrections.
> (the text limit is 10 pages).
>
> I have to submit the text on Wednesday afternoon, sorry for this
> late note.
>
> Thank you,
> Ashot
>
>