<div dir="ltr"><br><div class="gmail_quote">---------- Forwarded message ----------<br>From: <b class="gmail_sendername">Buddhini Waidyawansa</b> <span dir="ltr"><<a href="mailto:buddhini@jlab.org">buddhini@jlab.org</a>></span><br>Date: Wed, Oct 15, 2014 at 3:15 PM<br>Subject: Re: [Qweak_bnssa_elastic_ep_authors] Final draft of the elastic ep transverse paper - Comments due by October 17th, 2014<br>To: "Mark L. Pitt" <<a href="mailto:pitt@vt.edu">pitt@vt.edu</a>><br>Cc: Dave Mack <<a href="mailto:mack@jlab.org">mack@jlab.org</a>>, Paul King <<a href="mailto:pking@jlab.org">pking@jlab.org</a>><br><br><br><div dir="ltr"><div><div><div><div>Hi Mark<br></div>Thanks for all your comments. I must say I am overwhelmed but I see why you made them.<br></div>But let me see if I can convince you of my reasons to make all those bold statements and see if you agree with me. If not, I am hoping you'll help me to write out the parts you are really unhappy about.<br><br></div>My writing group consists of only me. I wrote the paper and send it out to Paul, Dave Mack and Katherine to get their feedback on the format and content. We didn't have group discussions but I did have individual discussions with all of them.<br><br></div>I'll go through your comments one by one and try to explain my side:<br><div><span class=""><br><span style="color:rgb(224,102,102)">Abstract: Some of these comments will make more sense after
reading my later stuff below. In general, I think the abstract
needs to have more details about OUR measurement and how it fits
into the existing body of measurements. The abstract shouldn't
have statements that aren't further developed in the paper
itself. <br></span></span><span style="color:rgb(224,102,102)"><font color="#000000">I thought the abstract was a place to get people's attention so they will continue to read the paper. So I structured it to introduce BNSSA and its relationship to TPE. Its importance as the only measurable observable of helicity flip amplitudes and a direct application (mu+p scattering) and then what we measured with kinematics. But I see your point about not having details in the body of the paper about mu+p and helicity flip amplitudes. I'll try to fix that. I'll also add something about the muli-pion states in TPE and how we see them to dominate model calculations at our kinematics.<br><br></font><span class="">
Specific sentences I am concerned about:<br>
* The MUSE sentence doesn't belong in the abstract. It is one
example among many of why this general topic is interesting, but
it isn't important enough to be in the abstract. This is an
article describing our measurement; it isn't a review article.<br></span></span></div><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">I don't have specific comment about MUSE. I talk about mu+p scattering. </span><br></span></div><span class=""><div><span style="color:rgb(224,102,102)"><br>
* The last sentence doesn't seem appropriate either. It is very
broad and you don't really support it further in the body of the
paper (ie. you don't describe other types of experiments where the
target polarization uncertainty is dominant). I don't know why
this sentence is here.<br></span></div></span><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">Ok. I'll remove the part about target polarization. But the statement about this being one of the precise asymmetry measurements is true. Right?</span><br></span></div><div><span style="color:rgb(224,102,102)"><span class=""><br>
* What is missing from the abstract:<br>
** In general, more about OUR measurement and where it fits in and
the "message" of this paper<br></span><span style="color:rgb(0,0,0)">But I feel I do talk about all of that minus the muli-pion states. I'll add that.</span><span class=""><br>
** The actual asymmetry we measure (with its errors) should be in
the abstract<br></span><span style="color:rgb(0,0,0)">Ok. I thought saying 2% measurement is more interesting than giving numbers.</span><span class=""><br>
** Make it a bit more clear that this measurement is contributing
to a body of measurements of this quantity, and its special niche
is forward angles<br></span><span style="color:rgb(0,0,0)">ok</span><span class=""><br>
** Indicate that we compare our measurement to available model
calculations and the conclusion of that comparison is ? (I'm still
trying to figure out what goes in place of the ? mark; see below).</span></span><br>
</div><div>Multi-pion resonances in TPE matter above 2pi threshold.<br></div><span class=""><div><br><span style="color:rgb(224,102,102)">First part of paper: "physics motivation"<br>
* My general impression is that there is too much space devoted to
observables that depend on the real part of two photon exchange.
I appreciate that you have taken the time to be very timely and up
to date with all those examples. But, as you know, we measure the
imaginary part of these amplitudes, and the relation between what
we measure and what is needed for those observables is not
completely clear (I know there is a dispersion relation that
relates them). I think this long paragraph can be edited so it is
just a list of examples of observables where one needs to know the
real part of TPE. Once again, this is an article about our
measurement - not a review article. To make it more about our
measurement, I would suggest having a paragraph prior to it which
indicates - in general terms - what BNSSA measurements already
exist on the proton and what our special kinematic niche is. Make
it very clear that we measure the Im part of TPE. Indicate that
there is in principle a relation between Re and Im, Then the
following paragraph describing all the interesting observables
where Re(TPE) arises seems well motivated.<br></span></div></span><div><span style="color:rgb(224,102,102)"><font color="#000000">For the physics motivation, I was trying to build on the importance of observables of TPE (Real and Imaginary both)</font>. <span style="color:rgb(0,0,0)">But I'll add things about the relationship between Real part and Imaginary part of TPE. I actually had those in there before but I removed them. It's what everybody writes in their papers so I thought I can just avoid that part and emphasize on why TPE matter at low Q2. Everybody is looking at high Q2 because of the Rosenbluth discrepancy and if we are to promote our result as a tool to test TPE models we need to say why TPE matter at low Q2. </span><br></span></div><div><span style="color:rgb(224,102,102)"><span class=""><br>
** Let me give just one example of why I think there is too much
space devoted to the Re(TPE) stuff. The last part of that
paragraph goes on at length about the TPE corrections in the MUSE
measurement, and - given the amount of ink devoted to it - I think
the reader is left with the impression that our measurement is
very important for sorting it out. But I think that leaves the
wrong impression on several counts:<br>
** It is important to have an estimate of the TPE in the mu-p
scattering measurement for planning purposes, but after all the
MUSE folks are not relying on that. They will measure all four
possible scattering combinations - so they will measure the TPE
effect, not rely on a theoretical calculation.<br></span><font color="#000000">Katherine told me a similar thing about what they may use for TPE corrections. But there is only one published TPE model calculation available for MUSE. Katherine told me MUSE will use Afanasev's calculation since it predicts a smaller correction that Mark and Tomalak. Afanasev doesn't have any published models for MUSE but in one of his talks given at MUSE (<a href="https://indico.psi.ch/getFile.py/access?contribId=10&sessionId=2&resId=0&materialId=slides&confId=1854" target="_blank">https://indico.psi.ch/getFile.py/access?contribId=10&sessionId=2&resId=0&materialId=slides&confId=1854</a>) he comments that it is hard to do these calculations due to the lack of information on the intermediate states. MUSE can measure TPE for e+p using sigma_ep/sigma_pos+p ratio which gives Re TPE but they can't do that for mu+p as far as I am aware of since they need an observable that gives access to the amplitudes F4 - F6 (coming from the imaginary part of TPE). Even if MUSE do or don't use Tomalaks calculation, we should not avoid putting it to our paper and letting somebody else take the credit for saying our measurement can be used to benchmark TPE models used for TPE corrections on mu+p scattering.<br><br><br></font><span class="">
** Does good agreement of the Im(TPE) with our (and other results)
really ensure that the same model properly predicts the Re(TPE)
effect? I have never seen that asserted quite so boldly in the
literature as you do here. I read the Tomalak/Vanerhaeghen paper,
and they don't assert anywhere that BNSSA measurements are needed
to benchmark their calculations (and I didn't see it in Mark's
talk at PAVI either). In fact they don't mention them at all.
But our paper seems to indicate it is very important. (Contrast
this to the gamma-Z box situation where even the first
Gorchtein/Horowitz paper made it very clear that PVDIS data would
be important for benchmarking their calculations).</span></span><br>
In page 5 of Tomalaks paper they do mention about beam normal spin asymmetries. "G4 appears in the expression for the beam normal spin asymmetry up to the factor nu/M^4". <br><span style="color:rgb(224,102,102)"><font color="#000000">TPE
corrections on Mu+p scattering is the only place where BNSSA
measurements can directly be used to test models without using hand wavy
arguments or dispersion relations. I talked with Mark during PAVI when
I found out about this from him. Actually during his talk, Mark made the comment to David
Armstrong that this is where your BNSSA measurements are important.
Later we discussed it more and he asked me to talk with Tomalak. I met
Tomalak at GRC where we had a long discussion about what he is
calculating and what we are measuring. He actually used the same model
he is using to get the TPE corrections to predict our results and came
up a factor of 2 lower. He only uses elastic states in his model and after
much discussions he was convinced that he needed to include the
inelastic states since his mode cannot predict our Bn result. He
immediately started working on that part. So as you see, our result is already being used to improve his TPE model.<br>Few weeks back I wrote to
both Mark and Tomalak asking them to review what I wrote about mu+p TPE correction on our paper
(lines 94 - 106). Tomalak replied back with modifications which are what I
included in the curret draft of the paper.</font></span> So as you see Mark, there was lot of discussions going on about this between me and Tomalak and that is what I based my conclusions and statements on. I should add private communication to these statements to make them legitimate and to avoid confusion.<br><br><span style="color:rgb(224,102,102)"><span class="">----> I guess my general point about this motivation section is
that there are many comments about the situation that are not
appropriate for us to be making. Examples are: "would benefit
from improved TPE models", <br></span> <span style="color:rgb(0,0,0)">I will add a published reference to this.</span><span class=""><br><br>"only way the model prediction can be
will constrained", ... </span><span style="color:rgb(0,0,0)"> <br>I will add private communication with Tomalak to this statement. </span><br><span class=""><br>These are conclusions that we as a
collaboration are not qualified to make. <br>They might be
appropriate for a single (or few) author review article on the TPE
topic, since they represent the opinions of the review article
authors. But the Qweak collaboration shouldn't be making these
kind of statements and conclusions about that whole field. Those
are the kind of comments and conclusions that need references to
papers by expert authors who people do trust to make those
conclusions. If those conclusions were stated in a paper or
conference proceeding, then it might be reasonable to include them
with a reference.</span></span><br>
</div><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">I
don't understand why we can't make these observations as physicists or
researchers. Is it because we (Qweak) are labelled as experts in PVES field? I have worked hard to learn about both PVES and BNSSA fields. Its not just that I did the analysis. <br>I did my research and talked with theorists who agree with the statements I made. I can't refer publications for these because all of these are based on private communications. As you see,Tomalaks paper was published in July this year so you cannot expect me to find proceedings or publications or other experimental evidence to support these claims.</span> <span style="color:rgb(0,0,0)">But I am really confused why you say we are not qualified to make these statements Mark. </span></span><br><span class=""><br><span style="color:rgb(224,102,102)">Last part of paper: This is an important part of the paper. We
need to - as a collaboration - come to a consensus on what the
message is here. Many of the statements made here are bolder than
I have seen written in the literature before and are once again
conclusions the Qweak collaboration cannot make on their own. I
know that much of what is written here was stated in your thesis,
and I assume that it was based on discussions with theorists. So
maybe it is simply a matter of supporting some of these statements
with references to private communications or conference
proceedings where these statements were made. <br></span></span></div><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">Me and Paul made those conclusions for my thesis but you are right, we need to be careful here not to step on anyone's toes.</span><br></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000">I actually have a discussion going on with Barbara, Misha and Andrei about this last paragraph (219-251). They agree about the multi-pion vs single pion comparison. I am still waiting to hear from Barbara. So the last section may be softened a bit next time I sent out the paper. But I will send you that perticualr section before sending it out to the collaboration to get your opinion.</font><br></span></div><span class=""><div><span style="color:rgb(224,102,102)"><br>The other thing
that is missing here is some notion of how we fit in with the
other small angle data (the two G0 points and the HAPPEX point).
You have some mention of it (G0), but you don't mention HAPPEX
(which also agrees with the Gorchtein prediction, unlike the G0
points). <br></span></div></span><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">I picked G0 since it is the first one to notice the differences in these 3 specific models. My conclusion involves the 3 calculations so I can't use HAPPEX to verify that further when they don't have Barbara's calculation (single pion vs multi-pion). So that's why I didnt add HAPPEX result.</span><br></span></div><span class=""><div><span style="color:rgb(224,102,102)"><br>
Some specific concerns:<br>
** Discussion about the D and F states in Pasquini. I have heard
you state this before, and it sounded reasonable to me. But as
stated here, I have some questions. If the Delta really dominates
at our kinematics, then how come adding in an extra 50% for D and
F will fix the problem? I assume they are already in there
because their dominat decay mode is in fact single pion. <br></span></div></span><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">Andrei thinks the continuum will also play a role in increasing the asymmetry here. But he and Misha are both not sure about what resonances would come into play. So I am going to remove this statement. It was a so-so one anyway. I guess I was waiting for somebody to tell me it is lame.</span><br></span></div><div><span class=""><span style="color:rgb(224,102,102)"><br>
** Your statement that "our precise measurement confirms with a
high confidence level that single-pion excitations do not ...." is
much stronger than you have stated in talks. At PAVI you said:
"Our precise measurement indicates at forward angles, B_n favors
models with multiple pion excitations with the nucleon." That
seems to me a more defendable statement. <br></span></span><span style="color:rgb(224,102,102)"><span style="color:rgb(224,102,102)"><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">At
PAVI I was trying to avoid not saying things I was planing to add in
the publication. Cos then I have to add it into the proceedings and I
didnt want the proceedings to come out looking like the paper.</span></span><span style="color:rgb(0,0,0)"></span></span><span style="color:rgb(0,0,0)"> It was like showing the preliminary result even though we have a final number. I was saving all the good stuff for the publication : )</span><span class=""><br>It is not 100% obvious
to me that there aren't other differences between those models
that could cause the differences. Have all the theorists agreed
that this is the main reason for the difference? </span></span><br><span style="color:rgb(224,102,102)"><span class=""><span style="color:rgb(224,102,102)">If so, then
let's have a reference to a conference proceeding or private
communication that supports that claim.<br></span></span><span style="color:rgb(0,0,0)">Andrei and Misha did agree on this. Barbara have yet to respond. Andrei claims that when he include single-pions in his model he get the same value Barbara gets from her model.</span> <span style="color:rgb(0,0,0)">I see I have to add private communication here.</span> <span style="color:rgb(0,0,0)">I realize if I had add them in lot of places it would have been clear to you where I got these ideas from. My bad.<br></span><span class=""><br>
** Do Afanasev and Gorchtein agree with your conclusion about the
difference in their calculations? I looked at Gorchtein's paper,
and I couldn't find such a clear statement about the difference,
but perhaps I missed it. If there is a clear statement about this
somewhere, then it needs to be referenced.<br></span></span></div><div><span style="color:rgb(224,102,102)"><span style="color:rgb(0,0,0)">They told me so long time back. I'll check with them again.</span><br></span></div><span class=""><div><span style="color:rgb(224,102,102)"><br>
** Your last two sentences make pretty bold statements about the
importance of these types of measurements for improving the
Re(TPE) estimates for other observables. It is much more bold and
definitive than I have seen in the literature before. Usually
just vague, general statements are made about the connections. I
always assumed that was because nobody has written a convincing
statement about the connections.</span><span style="color:rgb(224,102,102)"> Is there a reference that does
that? If so, quote it here. For me, I see the vague general
connection, but beyond that I would need to be convinced. After
all the dispersion integral is over a wide range of kinematics.
Just because we measure some observable that agrees with a model
in a certain kinematic range doesn't mean that model will give the
correct Re(TPE) prediction when you integrate it over the broad
range of kinematics needed to do the dispersion integral<br></span></div></span><div>You are pointing out another use of BNSSA that I should add to the paper.. It is a way to test dispersion integrals and Misha makes that exact claim on one of his papers so I have a reference for that.<br></div><div>But yes the claim about real TPE is a bit shaky and Misha told me so yesterday. What I actually wanted to say here is that any model of TPE should be able to correctly predict observables of real TPE and imaginary TPE. So in that way, BNSSA can be used to test models that are used to predict TPE corrections for ep scattering. Do you have a better suggestion for this?<br></div><span class=""><div><span style="color:rgb(224,102,102)"><br>Okay, I know that is a lot of comments, but hopefully it gives you
a flavor of my concerns. I know I haven't given a lot of
suggestions of how things should be modified to address my
concerns. But I can't really do that until I understand what the
collaboration's desired "message" is with this paper. Then it is
clearer what to write. I have discussed this with a few people,
and there is some agreement with aspects of what I say. So I'm
not the only one that feels this way. </span><br>
</div><div><span style="color:rgb(224,102,102)"><br></span></div></span><div><span style="color:rgb(224,102,102)"><font color="#000000">I now understand the reason behind most of your comments was lack of clarity or use of proper references on my part. I hope with all the explanation I am sending you now, you will see why I wrote what I wrote on the paper. You are the only one who have so far gotten back to me about these bold statements I have made in the paper. I was hoping to get these types of comments in the first round and the only big suggestions I got were from Greg and Katherine. So I thought the rest of the collaboration was happy about what I wrote. But then I got these from you and I was like Oh no..... but I really appreciate your feedback Mark. I know it takes a lot of work to read through all those references. I just wish others who have talked to you about this paper would have also written to me about their concerns. <br><br></font></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000"><br></font></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000">Feel free to call me any time you want tomorrow or the day after tomorrow and we can discuss these issues further. I am also wiling to have a phone discussion with others. Maybe you can arrange the meeting since I have no idea who would likes to be part of this discussions.<br></font></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000"><br></font></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000">Thanks!<span class="HOEnZb"><font color="#888888"><br></font></span></font></span></div><span class="HOEnZb"><font color="#888888"><div><span style="color:rgb(224,102,102)"><font color="#000000"><br></font></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000">Buddhini<br></font></span></div><div><span style="color:rgb(224,102,102)"><font color="#000000"><br></font></span></div></font></span></div><br></div><br clear="all"><br>-- <br><div class="gmail_signature"><div dir="ltr"><font face="georgia, serif">-------------------------------------------------------------------<br>Buddhini Waidyawansa<br></font>Postdoctoral Fellow<br>
C122,<br><div><font face="georgia, serif">12000 Jefferson Ave,</font></div><div><font face="georgia, serif">Newport News, VA 23602.</font></div><div><font face="georgia, serif">TP 757-912-0410</font></div></div></div>
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