[Clascomment] OPT-IN: Shrunken particles pass freely through nuclear matter

[Daniel Carman]

					June 7, 2011


Dear Lamiaa, Kawtar et al.,

I have read through your draft Nature paper on color transparency
and pass along my comments to you below. My general impression is that
the paper is written in a very choppy and uneven style that will
need some work and some polish before the editors at Nature would
even consider this for publication. Further, there is quite a bit of 
jargon here that the general reader will not understand. An article
for this publication needs to be written for a much different audience
than PRC or PRL. To be frank, this draft read to me like a conference 
proceedings. Hopefully by the time this review is completed, you will 
get enough feedback to improve the draft such that the introduction,
descriptions, and explanations are much crisper and more carefully
approached. If you have any questions on what I include below, let me 
know. 


			   Regards,

				  Daniel

********************************************************************
Page 1:
 - Line 1. You introduce the notion of hadrons by citing the proton
    and neutron. Yet you really care in this work about mesons. It seems
    like the introduction should take care to introduce both baryons with
    the familiar proton and neutron, but also the mesons. Together these
    strongly interacting objects are referred to as hadrons.
 - Line 7: Your terminology "normal hadron" is not clearly defined before 
    you introduce the notion of an "exotic configuration". You should 
    attempt to explain the difference at least in terms of longitudinal
    and transverse dimensions taking care also to clearly explain what is
    "exotic" other than its smaller size.
 - Line 9: Awkward wording. How about "However, QCD predicts that exotic
    configurations of hadrons can be formed that pass through matter with
    much reduced interaction probabilities compared to normal hadrons." But
    I think you also need to more clearly explain why this is the expectation.
    Just because the q-qbar is small in size, which should the color field
    interaction with other quarks in the medium be reduced. This does not
    come out clearly.
 - Line 11: What do you mean by "extremely small size"? Be quantitative here
    specifically stating the size scale.
 - Line 12. You introduce the term "attenuation", but this is not defined
    or described to this point.
 - Line 12. "strong cancellation between the color fields of their quarks." 
    What quarks are you referring to? Those of the meson or the target
    nucleons? The modifier "their" is unclear.
 - Line 13. You use the expression "dramatically reduced". This seems a bit
    of an over statement given the size of the effect being at the 10% level.
 - Line 15. You use the term "very high energy" and "lower energies", but
    these scales are relative. Be quantitative about describing the scale.
 - Line 17. You do not clearly introduce your experimental approach here.
    You should specifically state that you are studying the transparency
    effect using the electroproduction of rho mesons. You refer to a scattered
    electron and mention a rho, but you don't clearly state the reaction. Fig. 1
    seems like it needs to be referenced earlier in the description.
 - Line 18. You use the word "particles" when you should use "hadrons".
 - Line 22. "as its energy increases". This is unclear. Be specific and state
    the energy range.
 - Line 24. Why do you explicitly state the result for one nucleus and not
    the other?
 - Your introduction does not really get the impression across what the big
   deal is regarding transparency. It sounds like a trivial geometry argument
   the way you describe it. As Q2 increases, the rho gets smaller, so it
   more easily slips through the nucleus unnoticed. What is it about this
   affect that is so important for advancing our understanding of QCD and
   the structure of strongly interaction particles in the nuclear medium.

Page 2:
 Paragraph 2.
  - Line 6. Use "... are close together, forming a small-sized ...".
 Paragraph 3.
  - Line 8. Here and elsewhere you use the term "dilatation". The standard
     terminology is "dilation".
  - Line 10. I suggest "mass number dependence" instead of "A-dependence".
  - Line 10. "Diffractive dissocation" is jargon.
  - Line 11. "di-jets" is jargon.
  - Line 11. What is meant by "low and intermediate energies"? Need a scale.
  - Line 17. What do you mean by "reabsorption"? The prefix "re" means again.
     What is being absorbed and then absorbed again?
 Paragraph 4.
  - Line 4. "factorization" is jargon. GPDs are jargon. This sentence "Furthermore,
     the onset of color transparency ..." needs to be written for the appropriate
     audience. It conveys very little information as written.
  - Line 8. Same with the sentence about the "anomalous increase with centrality".
     This is not going to be understood by the readers.

Page 3:
 Paragraph 1.
  - Line 1. I suggest "... effort has gone into ...".
  - Line 2. Use "While searches using ...".
  - Line 10. Here you say "Another Jefferson Lab experiment ...", but you have not
     mentioned any previous JLab experiments.
  - Line 13. Here (and in several other places) you use nuclear transparency. You
     should consistently stick with color transparency.
  - Line 14. Use "... at still higher momentum tranfer would be ...".
 Paragraph 2.
  - Line 1. "Diffractive" is jargon. Should be made clear what you mean.
  - Line 1. Use "... provides the tool of choice".
  - Line 2. What do you mean by "simplicity of the production mechanism"?
  - Line 5. Use "materializes".
  - Line 9. The sentence "Intuitively, one would expect ..." is not intuitive to
     me. Seems like this is an important argument to make very crisply without
     the hand-waving approach you have taken. Furthermore, the argument needs to
     be made clear if and where such effects could be seen with the pion as a
     test probe.
 Paragraph 3.
  - Line 2. Use "... the photon can fluctuate into a ...".
  - Line 8. You say that no absorption is expected in deuterium. You should complete
     the argument by giving the size scale of deuterium relative to the
     coherence length. Also, "no absorption" is not theoretically justified. Little
     absorption is justified.
  - Line 14. Give the nuclear radii for C and Fe. Furthermore, is there a geometric
    argument for the size of the effect expected as a function of mass number?

Page 4:
 Paragraph 3.
  - Line 5. How is the Q2 slope defined? Is this some definition that you created? What
     are the limits in Q2 over which you defined this "slope"?
  - Line 8. The whole discussion of the models is not very well laid out. This
     comparison of models with data is completely vacuous without describing what 
     physics is included in the models. This is really important to elucidate to give a
     better explanation of the importance and "meaning" of color transparency from
     a dynamical point of view. Right now the curves on the plot are just "window
     dressing". This is a critical weakness in this manuscript. How seriously should
     I take these models? Is it possible that more trivial nuclear affects can explain
     what is observed? I just don't get a sense of the answers to any of these obvious
     questions from what you have written. Also, what are the theoretical uncertainties?
  - Line 25. You mention the CT signature in proton measurements. However, earlier
     you said there were no CT signatures in baryon measurements.
  - Line 29. You introduce the notion of "expansion time". Isn't this more aptly
     termed "expansion distance" given that you give distance units? Also, is this
     some aspect of the models that is based on some dynamical modeling or is it a 
     parameter just stuck in by hand in some ad hoc manner?

Page 5:
 Paragraph 1.
  - Line 3. Again you use the term "reabsorption". This is not clear.
 Paragraph 2.
  - Line 21. Use "... were also corrected for acceptance ...".
 Paragraph 3. 
  - Line 1. Use "... spectrometers (called sectors) each ...".
  - Line 5. The sentence describing the vertex resolution of CLAS seems
     misplaced. It should go after you talk about the z-separation of the
     the targets.

Page 6:
 - Line 1. Use "the CC and EC signals,  while pions ...".
 - Line 6. Use "... CLAS acceptance, while maintaining ...".

Page 7:
 - Figs. 2 and 3 captions describe "inner and outer" error bars. Your symbols
    on the figures seem like they should have horizontal ticks at the upper
    and lower ends to the full uncertainty.
 - Fig. 2 caption. Use "... as a function of the coherence length ...".
 - Fig. 3 caption. Use "systematic uncertainties". Also, here you slip back
    into "nuclear transparency". Be consistent and use "color transparency".

Page 8:
  - Fig. 4. You are not consistent with your usage of "c" units. You should
     label mass axis with GeV/c**2.
  - Fig. 4 caption. Sloppy wording on "peak and its width are similar". You should
     say that peak position and width agree with the PDG values convoluted with
     detector resolution effects for all targets.