[Deeppwg] Fwd: NSTAR proceedings

[Daria Sokhan]

Dear everyone,

Thank you very much for the comments!

First of all apologies for not spell-checking before sending it round, I
finished very late and forgot to do that, thanks for picking up all my
typos (slightly horrified by how many there were...)! To avoid spamming you
with ten emails I'll answer all of the comments here, roughly grouped (some
of them overlap):

Hervé, many thanks for the fixes on the theory parts, I'll put them in!

Volker, Michel, Silvia -- on the matter on the two asymmetries: I agree
that TSA doesn't look as good and given all the conflicting opinions, the
uncertainty on whether I can even release this from CLAS and the fact that
I somehow need to squeeze it all into four pages (with the extra bits of
clarification and references), I think it may just be simpler to remove it.
It's really very preliminary and indeed a "raw asymmetry" -- I'll just
refer to the analysis in the text instead.

Silvia, thanks for the comments, the asymmetries are defined in the
standard way (difference of numbers of events over sum), I omitted the
formulae for space reasons but I can add them. Not all the correction
factors are included: no pi0 or any other background subtraction except
what is reduced via exclusivity cuts; the dilution factor is also not
included in the displayed fit parameter on the TSA (I get about 0.5 for
it); I'm not sure what you mean by polarisations, though -- these are
assigned on an event-by-event basis so should be correct. However, I don't
think these features are necessarily an issue, the magnitude of the real
asymmetries is quite likely different from what is seen in the fit, but
that is what can be expected from the "preliminary"  label -- these are
just proceedings, so a write-up of my talk which presented an analysis in
progress. I will add a sentence to make it more explicit that not all
corrections are applied. I use the two fitting functions which are
suggested by the literature in the respective cases -- I agree that there
should be a reference, I'll add it! But if anyone is misled by comparing
parameters from two different functions applied to distributions from two
different variables, well, I think they should read the paper more
carefully -- p0, after all, is a fairly standard way of designating the
first parameter of a fit and I think it's implicit that this is not the
proper symbol for a particular variable. In any case, the TSA will be
removed. I'll add a reference and a brief comment for the VGG (space was
too limited to go into details!).

Michel, thanks for the corrections -- please see answers for the non-typo
points below:

*abstract, l.3:
"Data from both proton and neutron targets is required for an extraction of
all accesible GPDs...". It is not clear to me what are the "accessible
GPDs" ? What are the "non-accessible GPDs" ?
-- valid point!

*l.8: "scintillator wall". It might be strange to call our IC made of
PbWO4 crystals "scintillator wall". "Scintillators" refer to something
else in general.
-- Lead tungstanate is a scintillator, surely? Isn't scintillation light in
it how we detect the photons? I can say "wall of scintillator crystals" to
make its segmented nature more evident...

*par.2, l.7: "the recoil electron". A bit strange. "scattered electron"
rather ?
-- Agreed!

*l.14: "W>2 GeV/c2" Sometimes you use the "c" and sometimes not
(line below: "Q2>1 GeV2"); you probably have to choose and stick to one
notation.
-- Absolutely, I lost the c^4 on Q^2.

*l.16: "factorisation...into a hard-scattering and a soft-scattering part
applies". You never introduced those "hard" and "soft parts". It seems
to come out of the blue...
-- I wanted to motivate those cuts in brief, but I agree this is a little
oblique. I will see how much space I will have and will either take it out
completely or explain in brief.

*last sentence of par.2: "(to estimate which the same particle
identification and distribution cuts were applied to 14ND3 data)"
sounds bizarre.
-- I agree that was a bit condensed. Volker, to also answer your question
on this: I mean I subtracted the distribution obtained after applying
exactly the same cuts on NH3 data, from what I had on ND3 (normalised).
This enhanced the features which are due to the neutron in the deuteron, so
the effect of the exclusivity cuts could be checked. Some
neutron-in-nitrogen background is, however, still present in the data used
to make the asymmetries (analysis-wise this is to be addressed when my
teaching stops for the year!).

*p.5, bibliography: "[5]:... PRL 99". ->"Phys.Rv.Lett."
[6]: instead of "private communication", you can probably refer
to the original CLAS proposal. This is true that I/we should publish on
n-DVCS some day.
-- I was going to ask you about that! I'll reference the proposal, had left
it as a place-holder in case there was another publication.

And sorry for making GPDs complex, that was a late-night glitch, thanks
everyone for spotting that!

I'll circulate an updated version,

Many thanks again,
Daria


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr Daria Sokhan
Kelvin Building - Room 505
School of Physics & Astronomy
University of Glasgow
Glasgow G12 8QQ
UK                                                tel: + 44 141 330 2774
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On 1 December 2015 at 12:40, Silvia Niccolai <silvia at jlab.org> wrote:

> Hello Michel/Daria,
> the main problem I see in showing those two asymmetries side by side is
> that it is not clear to me, and it is not explained in the text, how they
> are defined. Both asymmetries needs various correcting factors
> (polarizations, backgrounds, and for the TSA there is the dilution factor)
> that I am not sure are at this stage included in Daria's plots. So, the
> magnitude of the real asymmetries could be different from what is shown.
> besides, as you pointed out, the different choice of fitting function for
> the two observables can be misleading for whoever may end up just looking
> at the value of the p0 parameter in the fit window...
> If we want to keep the two observables, they were they are defined should
> be clearly stated, and the choice of fitting function should also be
> motivated.
> Best regards,
> Silvia
>
>
>
> On Tue, 1 Dec 2015, GUIDAL Michel (57321) wrote:
>
> Hi Daria,
>>
>> Some more comments in addition to Volker's and Silvia's:
>>
>> *abstract, l.3:
>> "Data from both proton and neutron targets is required for an extraction
>> of all accesible GPDs...". It is not clear to me what are the "accessible
>> GPDs" ? What are the "non-accessible GPDs" ?
>>
>> *introduction, par.1, l.1: "The most complete information..." might be
>> too strong, there are probably things on nucleon structure which cannot
>> be accessed through GTMDs. "A wealth of information..." or something like
>> that to be cautious.
>>
>> *l-7/8: two times "the".
>>
>> *par.2, l.11: "extraction of the real parts of GPDs...". Silvia pointed
>> it at some other place above, here it comes again: GPDs are real.
>> Also, I wouldn't say that "cross-sections and double-spin asymmetries
>> allow the extraction of the real part...", they are "sensitive to".
>> For the true "extraction", one needs more than these 2 observables.
>>
>> *par.3, l.4: "the imaginary part of the GPD E". Again, GPDs are real.
>>
>> *l.5: "acesSible". Also, I would remove the "however", I don't see any
>> contradiction with the fact that E is the least known.
>>
>> *p.2, 3 lines below eq.1. "This paper..." is not very nice. "These
>> proceedings", "This article",...
>>
>> *section 2, par.1, l.6: "electRon".
>>
>> *l.8: "scintillator wall". It might be strange to call our IC made of
>> PbWO4 crystals "scintillator wall". "Scintillators" refer to something
>> else in general.
>>
>> *par.2, l.7: "the recoil electron". A bit strange. "scattered electron"
>> rather ?
>>
>> *l.13: "stacettering" !!!
>>
>> *l.14: "W>2 GeV/c2" Sometimes you use the "c" and sometimes not
>> (line below: "Q2>1 GeV2"); you probably have to choose and stick to one
>> notation.
>>
>> *l.16: "factorisation...into a hard-scattering and a soft-scattering part
>> applies". You never introduced those "hard" and "soft parts". It seems
>> to come out of the blue...
>>
>> *last sentence of par.2: "(to estimate which the same particle
>> identification and distribution cuts were applied to 14ND3 data)"
>> sounds bizarre.
>>
>> *par.3, l.1: "traget".
>>
>> *Fig.2: I am not shocked by the target asymmetry. Maybe, there is
>> no signal indeed but still this is information. I have no
>> problem to leave it but no problem as well to remove it. Actually,
>> the overall question is what is allowed to be released according to the
>> CLAS rules ?
>> By the way, in the caption, why do you fit the BSA and the TSA by 2
>> different functions ?
>>
>> *p.5, bibliography: "[5]:... PRL 99". ->"Phys.Rv.Lett."
>> [6]: instead of "private communication", you can probably refer
>> to the original CLAS proposal. This is true that I/we should publish on
>> n-DVCS some day.
>>
>> Amities,
>>
>> Michel
>>
>> ***
>> Michel GUIDAL
>> Institut de Physique Nucleaire
>> Bat 100 - M130
>> 91406 ORSAY Cedex
>> Tel: (33) 01 69 15 73 21
>> Fax: (33) 01 69 15 64 70
>> E-mail: guidal at ipno.in2p3.fr
>> ***
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>>
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