[Primex2] draft text for CD-2015 proceedings

[Aron M Bernstein]

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.jlab.org/pipermail/primex2/attachments/20150928/a5a5f81b/attachment-0001.html>