Questions to EB 28.8.2020
================
Compiled by IA(editor), commented by AMCS.
Strategy:
-=-=-=-=-
The EB provides guidance for the update of the draft for the reading.
First: Go through "easy" issues.
Last : Decide on "difficult" issues. [marked 我的天 ..... 我的天]
The update will focus on content.
Textual comments will be considered at the reading; exception title.
Wishes on title:
----------------
'Impact of jet production data at NNLO on the
determination of HERAPDF2.0 parton distributions
and on alpha_s(M_z)' [EL]
'Measurement of HERAPDF2.0 parton distributions and alpha_s at NNLO with
HERA jet production data" [IK]
(editor: PDFs cannot be measured; alpha_s should be in the title)
AMCS--how about 'extraction' rather than 'measurement'
Requests to change the analysis:
--------------------------------
DH5
Line 139 :
The momentum sumrule is an integral in x from 0 to 1.
Given the conditions of our analysis the application of
the momentum sumrule is useless and only introduces a bias.
The reason is that an integration is required over
the full range in x for all Q2. The behavior of the pdf
at low x is unknown. Due to the triangular shape of
the phase space the constraint for increasing Q2 is getting
more and more uncertain, since there are no measurements for
low x, while the parametric x -dependence merely reflects the
evolved information from the low Q2-region.
Therefore, drop the momentum sumrule.
(editor: I don't think that the HERAPDF parameterisation and
treatment can or should be changed at this point.)
AMCS- We are not here to re-invent the wheel. The momentum-sum-rule has been
investigated many years previously, e.g. Thorne. It is now standard to use it.
Everybody believes in QCD we are no longer trying to challenge it but to use it.
Phrases which attracted objections
-----------------------------------
Even though it is explained in the text, there is a wish to
have exp/fit everywhere. Is this okay for the EB?
(editor:this would be good)
AMCS-I dont care much
The question of tension has been with HERAPDF2.0 all along:
Needs rephrasing towards "consistency" and "not more tension in jets
than in inclusive data". Is this okay for the EB?
(editor:this would be good)
AMCS-fair enough
The "negative gluon" term crept back, even though we should go back
to "alternative gluon". Is this okay for the EB?
(editor:this would be good)
AMCS-fine
Missing strategy
----------------
Introduction should describe better what the strategy is [JG]
(editor: would like to prepare something for update of draft
adrressing also the HF question)
Introduction
------------
J+NO do not want this to be the end. They want the HF data in the fit.
==> family is not complete
DH6 wants a discussion why we do not fit HF data
AMCS--not a discussion, just a comment please
(editor: it is stated at the end of the data section that
there are no complete NNLO predictions for HF and)
AMCS--it was my understanding that our colleagues- particularly those
who like the ABM fixed flavour scheme-- think that the NNLO is not
complete for HF. Thorne, whose scheme we use, thinks it is 'complete enough'
and certainly fits HF himself at NNLO. I never objected to its exclusion
because we established early on that its addition made no
discernable difference- apart from the Mc,Mb values.
You will not find me ever doing a new PDF with it in.
(editor: add a remark on this to the strategy)
Is that okay for the EB?
DH wants something on parameters---
(editor: we discuss what is needed the the appropriate place;
in the introductions we state that we use the HERAPDF2.0 papmeterisation)
AMCS--these are the standard HERAPDF2.0 parameters,
we did a check that they were still OKAY.
Structure
----------
SS:
Section 4 and 5/6 should be swapped. First we determine PDFs with fixed
alpha_s and compare to jets data. The free-alpha_s fits should come
after that (same order as in the summary). [SS]
(Editor:
The editor does not consider this reasonable as then we have to
use strange "forward pointing" to motivate the values that we use for
alpha_s
-- perhaps, the improvement of the introduction will make that
more clear.
-- adjust summary to textual structure)
AMCS--I agree with the editor--
Is this okay for the EB?
Some would like more emphasis on alpha_s, some want less emphasis.
(editor: leave as is)
Is this okay for the EB?
==>DH5
This would basically mean to rewrite the 2015 paper.
(editor: I think we agreed that we do not want this. Perhaps
an even stronger sentence pointing at this paper is needed in
the introduction when strategy [new] will be discussed}
AMCS--YES I think we need to tell them it has all been done
and published previously
Is this okay for the EB?
additional informtion/removals requested
-----------------------------------------
There is a wish that it is stated that
the jets were obtained with the kt algorithm and R=1.
Do the collaborations confirm that this is true in all cases?
Remind that it was established
(cite arXiv:1003.2923) that at HERA,
using the kt or anti-kt algorithms (as used at LHC)
is qualitatively equivalent.
(editor: Needs confirmation by collaborations)
Is that okay for the EB?
The significant requests of JG to add information -- see below.
Which of them are endorsed by the EB?
The significant requests by AL.
Which of them are endorsed by the EB?
J+NO would like comparsions of predictions to data points
which were removed.
(editor: I think they were removed because predictions make no sense)
DH1: Figures 7 and 8 are the comparison between the new analysis and
the old NNLO result.
DH2: He wants tables of parameters and correlations.
-- but seemingly a comparison for the two different alpha_s
AMCS--I doubt that anybody is interested, but I think he meant our
current correlation matrix for free alphas compared to a correlation
matrix for free alphas for the inclusive only fit. He wants to see if the
gluon/alphas correlation shows up more for inclusive alone. The answer is
YES of course it does, this is the point of jets, everybody knows this, we
don't HAVE to demonstrate it again, we are not writing a textbook.
(editor: keep what we have and explain it to DH,
if we have tables or correlations, they should be extra material)
What does the EB want?
scales:
-------
我的天 Should we keep scale uncertainties out of the abstract and summary
to avoid the issue of correlations?
Is this okay for the EB?
Or can we quote our main result? -- wanted by some comments[EL,..]
Or do we have to go back to both results? -- wanted by H1?
What does the EB decide.
(editor: would like main result)
AMCS-difficult one!
==> 我的天 EB
The correlation issue for the scale uncertainties; there is a suggestion
to phrase the 100% as traditional.
Is this okay for the EB?
DH wants to know why the two scale uncertainties quoted after line 281
are almost equal.
(editor: because the same procedure was applied --
does the EB want this to be written down?)
AMCS- Should not be done.
==>DH4
(editor: I don't really understand what is wanted)
However, it seems like he wants a lot more emphasis on scale choices for
alpha_s? And on the compatibility between fixed alpha_s and free PDFs and
free alpha_s and free PDFs.
This latter is shown in Fig2a which he didn't understand.
AMCS- I think the description is fine, this sort of plot is standard.
(editor: keep it as is and explain it to DH)
AG:
"scale uncertainties were not considered for the comparisons to data".
AG thinks thinks this is not acceptable.
AMCS--well it is what we did in 1506.06042--
AG:
The NNLO predictions have significant scale uncertainties
(from the jet matrix elements),
and these should be shown (separately). This is different from the potential
scale uncertanties of the PDFs that were discussed
in the previous sections, which can indeed not be usefully quantified.
(editor: Can this be done?
Do we have uncertainties from matrix elements available?
If yes, should it be done?)
AMCS-- It can probably be done if I understand him correctly
-- i.e. he wants the final PDFs fixed but alternative scales used.
But I don't think it should be done.
Comparisons to past publications:
----------------------------------
我的天
Should we keep Section 4.1. or stop after the first sentence and
add this somewhere in Section 4? [IA]
Should the rest go to the additional material?
AMCS--I say keep it as it is but this is modulo 'the bug'.
(editor: Please also consider that the previous results currently referenced
are also influenced by the problem in the NNLO predictions.)
--> EB 我的天
Should this section be enlarged comparing to other results[JG]?
Should there be a discussion on differences[JG]?
AMCS-- No to both of these, maybe a plot to show comparisons would be fine.
(editor: a plot would be nice -- only NNLO values)
Would the EB like that?
AG wants info from 278 at the beginning of the paragraph.
AMCS-- I think it is okay where it is
Main body plots:
----------------
in general:
Should any plots be removed or andy added?
The EB has to okay all figures.
specifically:
Data plots:
Should ratio plots be added? as panels?
---AMCS yes proably as panels
Should the log plots be removed?
--AMCS NO
Should anything from pages 28--30 be added to the main body?
Should anything from SS/MK plots be added?
These are the plots on high gluon and the plots requested comparing
at different alpha_s
Figures [AL]:
Fig. 2: a) not good choice of the light blue color (alpha_S free fit).
--AMCS is it not what we did before? but I dont care much
Is that the line passing through the blue points?
b) red points connected with a dark line. c) red points connected
with a red line. Why is the x-axis scale of a) different from b)
and c)?
AMCS--only b) and c) NEED to be the same axis
Figures [DH]:
Figs. 3, 4 and 7 the sea label in the figure and the captions are different.
AMCS noted already
Figs. 3-7 : Why is the green band for medium x broad for uv and not for dv ?
AMCS--that's just the way it works
(editor: I do not understand the following remarks)
Figure 2a : I don’t understand.
Are all parameters except for alpha_s free ?
AMCS YES
also the scales ?
AMCS NO the scale uncertainty is done separately
Note my remarks above. It seems to me vital to understand the
interplay between alpha_s and the systematics,
before any conclusion can be reached about the central value of alpha_s.
--AMCS--this interplay is taken into account by the the chisq whereby
systematic shifts of the data points are part of the formalism--it is NOT NEW!!!
Figs.3-7:
The figures for different alpha_s do not mean very much,
since the pdfs are part of the fit.
--AMCS almost exactly wrong, I dont think he knows what is going on--
Figure 8 : I don’t understand. What remains constant and what is part
of the fit ? What do you conclude ?
---AMCS--it is ALL part of the fit, but you have to do different fits
to evaluate model/param uncertainties-- again he does not know what is going on
Appendices:
------------
Should Appendix A be kept or made additional material?
(editor: should be kept)
AMCS-- I think we keep this appendix--
Additional material:
---------------------
Should scan plots as shown on page 27 stay as additional material--
AMCS-- NO
(editor: remove)
Is this okay for the EB?
Should all of the plots on pages 28 -- 30 stay as additional material
Should the additional plots requested by SS at the paper
presentation be in the paper, become additional material?
[As already said in the paper presentation, I would prefer very much to
have figure 8 or 15 with the same alpha_s for both PDFs. Using different
alpha_s blurs the message of the figure. People will possibly try
to relate the uncertainty differences to the alpha_s choice rather than
focus on the message of uncertainty improvements through the new data.]
== MS considers these plots rather misleading.
== AMCS--I think SS's plots at same alphas should be somewhere,
I dont mind where.
However: old fit cnnot be repeated with new alpha_s --
--> cannot compare to old fit at new alpha_s
(editor: if EB wants the existing plots, --> additional material)
What does the EB want?
Summary:
---------
Should it end with something more spectacular? [AL]
(editor: wants to change order to give alpha_s result first -- following
strategy of paper)
DH3: DH wants a long discussion what compatible means and whether we tested
QCD.
AMCS--NO, QCD is an established theory
(editor: Perhaps a nice sentence on the overall consistency
of the picture could make AL and DH somewhat happy.
If the EB endorses this, the editor will try to come up
with a suggestion.)
Is it okay for the EB?
References:
-----------
Halina’s name is mispelled in refs [2] and [21].—> Abramowicz.
refs [11] and [12] have the same arXiv number.
Change ref [12] to hep-ph/0609285
ref [17] V. Andreev et al.
[This will be fixed in bibtex -- must have been wrong for a while]
---------------------------------------------------------------------------
H1-JG
Significant: I list here all questions that are not just wording only.
==============
General: I miss a bit a general outline of the fit procedure.
We determine alpha_s and PDFs.
In the introduction one learns that we determine
both simultaneously. Then in 3.1 to 3.4 nothing is said on alpha_s.
Then alpha_s is determined fitting also pdfs, but discussed only
in context of scaling violations. And then alpha_s is unexpectedly
fixed to determine pdfs
which one had assumed to have been already determined together
with alpha_s.
To understand the paper more easily, I would like to have some
guidance early on.
Comparisons with other results in section 4.1 is a bit meager,
showing only the level of consistency, if data are treated similarly.
But the difference of the Results or the agreement is of interest
in first place. The paper could also compare
the result to other important analyses in different reactions. What is the
relevance of the result on alpha_s?
Comments in detail:
-----------------------
3.1 Choice ..
----------------
127 "extra parameters .. one at a time":
Is there some arbitrariness in which
sequence the further parameters were chosen?
Is the actual choice of parameters
depending on the sequence?
3.2. Model ..
----------------
What is done with alpha_s in these PDF fits?
Or the other way round, one wonders whether these variations
lead only to uncertainties on the PDFs and not on alpha_s.
In the introduction it is said, that fitted together.
153 what determined the variation of mu^2_f0?
3.3
-----
175 Here in 3.3 alpha_s is mentioned.
But what in 3.2? I already asked there.
191 but mu_f0 = sqrt(1.6) = 1.26 < 1.37.
One could check and state what happens then.
4
----
228 I guess (2,0 mu_r, 1,0 mu_F)
4.1
-----
269-277 The reader ist not so much interested whether data agree,
if treated the same way, but at least as much whether the results
are very different or not if different assumptions are used.
So the main results as they were presented should be compared as well.
282 Again the main focus seems to be on trying to do the same.
5
-----
305 if mentioned, what was then actually done,
which scale variations assumed, as for the alpha_s fit?
318-320 "The reduction in model and parameterisation uncertainty
... mostly due to the necessity to change the estimation procedure."
What does this mean?
Understandable? Further discussion is rather technical.
I would expect some words on the actual observations, like that the
largest effect is seen at large x.
Is it really significant as it appears to be?
--------------------------------------------------------------------------
H1-DH
Comments to the draft v.05-July 27, 2020
Impact of jet production on the NNLO determination of HERAPDF2.0 parton distributions
Dieter Haidt, August 24, 2020
The present analysis of the H1 and ZEUS data from HERA based on the inclusive processes as well as jet production within NNLO of pQCD is a major achievement and constitutes an essential part of HERA’s legacy. Some of the authors remember the very first steps performed by MARK at SLAC and Gargamelle at CERN, half a century ago, and appreciate the huge effort to arrive at the mature results of HERA. The huge progress on the experimental side is complemented by the equally huge progress on the theory side allowing now for a comparison at NNLO level.
DH1==>
The emphasis of the present analysis is to study the impact of data on jet production when added to the previous analyses of the inclusive data alone. Apart from increasing the statistics the unique value of jet production comes from the direct dependence of the gluon (lines 217-231). I suggest therefore devote the first chapter to discussing the improvement in the pdf parameters and their correlations determining the phenomenological parton distribution functions. The crux of all analyses is the limited knowledge of the gluon distribution function obtained from the triangular phasespace in (x,Q2). The jetdata provide a genuine new insight. Within the same framework : compare the parameter fit using the inclusive data alone with the new fit in this paper of inclusive data + jetdata. Illustrate it with two figures and make it quantitative with tables of the bestvalues and their correlations in both cases. Comments on the improved gluon distribution are welcome.
DH2==>
Thanks to Katarzyna I had a chance to study the correlation table of the combined data. I had anticipated strong correlations the gluon and the seaquark parameters and also between alpha_s and the gluon parameters, but to my surprise there are only rather moderate correlations with all pdf parameters. Perhaps the comparison with the correlation table using the inclusive data alone will elucidate my prejudice.
==>DH5
Line 139 : The momentum sumrule is an integral in x from 0 to 1. Given the conditions of our analysis the application of the momentum sumrule is useless and only introduces a bias. The reason is that an integration is required over the full range in x for all Q2. The behavior of the pdf at low x is unknown. Due to the triangular shape of the phase space the constraint for increasing Q2 is getting more and more uncertain, since there are no measurements for low x, while the parametric x -dependence merely reflects the evolved information from the low Q2-region. Therefore, drop the momentum sumrule.
==>DH6
The heavy flavor contribution is included through pQCD evolution from massless quarks. A remark would be in order, why we did not use our own direct measurements. Is it because of missing NNLO predictions ?
==>DH4
It is of particular interest to illustrate the impact of the systematic sources on the value of alpha_s. A figure showing the variation of alpha_s with the scale parameters would be revealing, since the uncertainty of the bestfit is dominated by the scale uncertainties. The parametric dependence should be done for fixed pdf, otherwise the effect may be compensated partially by adjusting the (many) pdf parameters. The point will be whether the value of alpha_s is significantly shifted when varying the scale parameters. If it turns out that the central value of alpha_s is little dependent on the scale uncertainties, then we have a strong argument that our determination in the spacelike region differs from the one in the timelike region, which is also affected by scale uncertainties.
==> DH5
The determination of the parton distribution functions and alpha_s are linked. The key to the understanding of our paper is largely related to the chisquare function and the way it is exploited. I suggest to devote a detailed presentation, technicalities may be deferred to an Appendice.
a. How is the chi2-function defined ?
chi2(p) = Term with matrix(yi,f,C) + Term with constraints
yi = measurements
xi = kinematic variables
f = prediction depending upon kinematics and free parameters
C = correlation matrix containing the uncertainties
p = alpha_s + pdf-parameters + systematic parameters
b. How are the systematic uncertainties implemented ? and in particular the splitting ?
c. Is the fit performed simultaneously for all free parameters ? Or in terms of fixed values for alpha_s ? Is the “so-called” chisquare scan a sequence of ch2-fits with fixed values of alpha_s including all other parameters as free, also the scale parameters ?
d. The chi2/dof is quoted as 1.2. Does this indicate an underestimation of some uncertainties, perhaps the scale uncertainties ? If so, would it be possible to repeat the fit with enlarged uncertainties to see the effect on the bestvalue of alpha_s ?
e. Is the meaning of chi2 the same everywhere in the text ?
f. Is the gluon distribution function dominating value and size of alpha_s among the pdfs ? How big are the shifts in alpha_s caused by the systematics in the pdfs and the scales ? Shifts are linear effects. It may be justified to average over some of them.
g. The determination of alpha_s is dominated by the systematic theory error of +-0.0024 compared to the experimental error +-0.001. One may ask whether the treatment of the systematics has an important effect on the central fit value of alpha_s (see point f)
Line 284 : why is the scale uncertainty almost equal to this analysis (and not bigger) ?
Figure 2a : I don’t understand. Are all parameters except for alpha_s free ? also the scales ? Note my remarks above. It seems to me vital to understand the interplay between alpha_s and the systematics, before any conclusion can be reached about the central value of alpha_s.
Figures 3-7 : Why is the green band for medium x broad for uv and not for dv ? The figures for different alpha_s do not mean very much, since the pdfs are part of the fit.
Figure 8 : I don’t understand. What remains constant and what is part of the fit ? What do you conclude ?
Line 344 : are we quoting the fit values and correlations for the two values of alpha_s assumed.
==> DH2
Line 347 : A careful discussion should be given qualifying “compatible”. Note my remarks above.
I suggest a much extended conclusion. I have - for my own sake - tried to highlight what we have achieved., since the present paper is perhaps the last word and therefore a legacy of HERA inviting some remarks on the overall increase in knowledge as well as some critical remarks on further improvements left to future studies. We may comment on the performance of the collider HERA, the experimental achievements of H1 and ZEUS with detailed publications and a final comparison with QCD (for the first time) at NNLO. The confrontation of experiment and theory provides a consistent picture.
==>DH3
The basic question is to what extent we have tested QCD. Our concern is perturbative QCD, which reduces the question to stating in which (x,Q2)-region pQCD is valid. This implies to worry about two frontiers (a) the transition in Q2 from the nonperturbative to perturbative regime and (b) the transition from moderate x-values to very low x-values. The first question is addressed by considering various starting scales in Q2, thus getting safe against higher twists. The other question, though important, may remain disregarded, since it concerns only the small tip in the phase space region at low Q2 and low x. Given the assumption that in the selected phase space region pQCD be valid the data are used to determine the parton distribution function, which are the necessary input to predict the observables. Since pQCD is applied at order NNLO (which is an achievement in itself), there is an intrinsic purely theoretical uncertainty coming from the truncation of the perturbative series. We address this uncertainty by varying the scales involved. Our conclusion about the impact of these systematic uncertainties will be decisive in judging the difference of our determination in the spacelike regime of alpha_s and the existing one in the timelike regime. In any case here is a task for future work in theory.
The determination of the parton distributions is of value in itself and represents an important achievement, although there are still several weak aspects : the a priori assumption of the shapes, specific assumptions regarding the flavours , in particular the unknown s sbar-quark contribution and the role of the gluon. It should be emphasized that all in all the present knowledge is remarkable.
The experimental information is shared between the determination of the parton distribution functions and the confrontation with pQCD. Is is possible to make an educated guess what fraction of the experimental information is actually available for testing pQCD ? The observation that the correlations between the pdf parameters and alpha_s are weak, is perhaps a strong argument in favour of real test of pQCD.
Our analysis demonstrates a consistent picture and complements the efforts in the timelike region.
--------------------------------------------------------------------------
H1-J+NO
Line 35 describes this paper as the "completion" of the HERAPDF2.0 family.
We think that this is too strong a word, since we see that there are
possibilities for still further steps; explicitly we think of future NNLO
calculations for heavy quark data involvement in the fitting. Thus, inclusive + jets + heavy quarks for the PDFNNLO fitting.
The heavy quarks enter also as Vector Meson Production, accessible to QCD calculations. In this connection we like to mention the paper arXiv:1908.08398 by C.A.Flett et al., "How to include exclusive J/psi production data in global pdf analyses".
We believe that inclusion of such HERA data will improve the uncertainty
situation at low x for the gluon PDF, once the corresponding NLO/NNLO
calculations are available.
Thus, we would not too strongly stress that the current paper is final,
as far as HERAPDFs go. Hopefully there is much more to come!
Chapter 2 describes in detail how several data points were exempted from
the analysis, for various technical reasons. In the final results, one
would like to see the predictions of the fitted PDFs for these points, which were NOT included in the fitting procedure. The paper makes the
statement that there is good agreement between the fits and the fitted
data, which naively is no surprise and only confirms that the inclusive
and the jet data are compatible. However, the reader gets curious and
wonders about the agreement (or possible disagreement) in the immediate
neighborhood of the fitting phase space, the neighborhood which is given by the left out data points.
--------------------------------------------------------------------------
H1-ZZ
deemphasize alpha_s
---------------------------------------------------------------------------
---------------------------------------------------------------------------
ZEUS-AG
Achim Geiser:
--------------
Thanks a lot for the great paper draft and the nice results.
I leave simple style comments to others, so please find my significant comments below:
section 4:
The "experimental" uncertainty is now even less experimental than it was before, since the hadronization uncertainties are
now also included. In some ZEUS papers we have just called it "fit" uncertainty, but I know that was not acceptable to H1.
So, my compromise proposal (similar to H1/ZEUS paper arXiv:1804.01019)
line 231: "exp/fit"
line 232:
"where exp/fit denotes the fit uncertainty based on the experimental input uncertainties and the hadronization uncertainty"
line 234:
"the fit uncertainty"
line 251: "The similarity ... no additional tension."
I don't think this is true. Similar chis/dof > 1 indicates similar tension, also in the jet data. Thus rather:
"The similarity of the chi2/d.o.f. values indicates a similar level of tension for the jet and inclusive data."
or
"The similarity of the chi2/d.o.f. values indicates that the addition of the jet data does not change the average level
of tension in the data."
or
"The similarity of the chi2/d.o.f. values indicates that the addition of the jet data does not increase the average level
of tension in the data."
line 259: "the negative gluon term" -> "the flexible gluon term"
There is nothing in this term that forces the gluon to become negative, nor can the gluon be prevented to become negative
(at low enough scales) even without this term.
A more flexible parametrisation can never bias the result, as long as the fit converges properly. A more restrictive one can.
Thus "could bias" -> "could significantly alter".
line 266: "the details" -> "these details".
It indicates nothing about potential other variations of the gluon parametrisation.
line 278: I would move this difference right to the beginning of the section, since it is a basic conceptual difference
that is the main asset of this paper w.r.t. the others.
The difference in the treatment of the scale uncertainties in the previous paragraph, although numerically more important,
is only a technical difference and should not be highlighted as if it were a conceptual one. Also, it could be stated that
the 100% scale correlation option is the "traditional" variant.
I am personally convinced the treatement we use use here is better than the traditional one, so I do *not* propose (and would strongly oppose) changing our default treatment.
---------------------------------------------------------------------------
ZEUS-AL
significant:
============
l. 37, remove sentence 'An analysis….family.'
l. 51, remove 'the analysis…at NNLO.' This belongs to the conclusions.
l. 73, ’several reasons’ - are they all listed in this paragraph?
l. 81, In Table I, ’normalised’ appears in the data set column and in
the caption. Is it obvious what is meant by normalised?
footnote 3, Is it clear why the value of 25 was chosen.
All it says is the it should be > 15.
l. 203, what is meant by ’technical reasons’?
l. 210, when trying to make a point about precision,
why use ~ for the uncertainty?
Section 3.4 is titled ‘hadronisation uncertainties’
so is the number given in l. 215 the one that was used here ?
It appears with ref [2], meaning it is probably the one used in that paper.
What is the number used for the present analysis?
lines 340, 360 …ZEUS and H1…Throughout the paper the order is alphabetic,
namely H1 and ZEUS. I thought it would make sense to keep this order.
l. 356, is this last sentence the highlight of the paper?
It would be nice to end this with a more significant statement.
______________________________________________________________________________