[Clascomment] OPT-IN: Demonstration of a novel technique to measure two-photon exchange effects in elastic e(+/-)p scattering

[Viktor Mokeev]

 Dear Mikhail,

 I have problem with your comment:
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2) Eq.1 is not fully correct - A_loop is a sum over all leptons and all quarks, hence I am not really sure what charge has to be put in front of it
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  How the photon-lepton QED interaction may transform the initial electron to any other lepton?! According to QED, it is not possible. Also, the photon interacts with the initial proton which has the electric charge equal to +1 (in electron charge  units). Electric charge is conserved quantity in any known interaction, while all complications related to the non-pointlike transition currents proton-blob  can be absorbed into the amplitudes A_{i} of Eq.1

 What do you mean in your comment?

 Best Regards,
                     Victor 

----- Original Message -----
From: "Mikhail Osipenko" <osipenko at ge.infn.it>
To: clasmbr at jlab.org, clascomment at jlab.org, carman at jlab.org, ggilfoyl at richmond.edu, mokeev at jlab.org, baraue at fiu.edu, maryam at jlab.org, niroula at jlab.org
Sent: Wednesday, May 15, 2013 4:26:14 AM
Subject: OPT-IN:    Demonstration of a novel technique to measure two-photon exchange effects in elastic e(+/-)p scattering

Dear Authors of TPE paper,

I have few suggestions for this draft:

1) abstract, second sentence: "limited experimental evidence" is not universally recognized yet, I would suggest more cautious "there is no unambiguous direct experimental evidence",

2) Eq.1 is not fully correct - A_loop is a sum over all leptons and all quarks, hence I am not really sure what charge has to be put in front of it,

3) sentence right after Eq.2 - probably you wanted to say "thus identical for electron and POSITRON" scattering." And proton antiproton as well - but it is better to omit proton charge discussion as irrelevant to this paper.

4) in Eq.3 use curved brackets to distinguish better from brackets of Re(),

5) below Eq.4 use "divergenceS cancel",

6) Eq.5 - \delta_2\gamma and \delta_br. - are finite parts of TPE and bremsstrahlung, so that R_2\gamma in Eq.6 is also the finite part of TPE contribution. I don't know what sense does it make to separate it from its divergent part.

7) you select elastic reaction by a number of angular cuts, but calculating RC using a naive prescription applicable to a measurement with only scattered lepton detected and a cut on its energy. Be prepared to face questions: why do you apply incompatible RC corrections?

Best Regards,
                  Mikhail.