[Clascomment] OPT-IN: A comparison of forward and backward pp pair knockout in 3He(e, e'pp)n

[Elton Smith]

1. leading paragraph, lines 45-53.
The first paragraph is deep in jargon and the language should be broadened for the benefit of non-experts. For example: "mean field nucleons" presumably refers to nucleons interacting in a potential described by the mean field of the nucleus, and corresponding to average nuclear densities. "SRC nucleons" reads "short range correlations nucleons," which  makes no sense. Call this nucleons tightly coupled through short range correlations? Perhaps a way to introduce the subject is to describe an ideal nucleus with a single average density and how nucleons in actual nuclei are affected by neighboring nucleons creating density fluctuations, which are produced by short range correlations.  In some ways the abstract contains language that is better suited for the introduction.

2. line 74. the correlation indicates... suggests? or may indicate? (How strong should this statement be?)

3. Acronyms inconsistencies. There are probably more than give below.
Usually, one uses the first introduction of a phrase and defines the acronym and then uses it consistently. I am referring to FSI and MEC
line 160: Final State Interactions mentioned (there might be an earlier mention) but no acronym. Note that words are capitalized. This is not consistent through out the document.
line 232-233 FSI and MEC defined
line 278: FSI redefined
line 288: MEC redefined
line 385-386 FSI multiply partially defined
line 430 FSI redefined
Caption Fig. 6. final state interactions spelled out once, FSI used once and meson exchange currents used. 
line 430 FSI spelled out and uses acronym.

4. Paragraphs. Too many paragraphs in some places, example
line 228
line 243-249

5. Statements of normalization.
Fig. 5. 4th line. "The theoretical calculations are all multiplied by the same arbitrary factor to approximately scale the full calculation to the data." 
Fig. 9. last line. "No scale factors have been applied to the calculations."
I do not think normalization issues were discussed in the text and these statements make it sound like arbitrary adjustments have been made to the theory to make a point. The rational for these decisions should be made clear, especially clarifying which calculations have been scaled or not. (The two statements above leave the reader uncertain about how curves on other plots are handled).

6. Suggestion: Add plot of lab momentum for detected protons and neutron.
At the point of paragraph lines 272-279, selection of protons with 0.4 to 0.6 GeV/c momenta. It would be useful generally to the paper to show the measured momentum in the lab for the protons and neutrons. Many plots are shown, but they all show higher level quantities.

7. Peak in Fig 8a. Discussion missing on the first bin of Fig 8a. What is it, why is there so much a discrepancy between data and theory.

8. Claims by the paper. How strong are they?
a) line 364-366. "This strongly indicates that at least one of the two distributions is not sensitive to the initial state momentum distribution." Can this statement be made? Or perhaps it implies that the two distributions cannot both be "dominated by the initial momentum state"?
b) line 380 "The Laget calculation agrees reasonably well with the data for p_rel>0.5 GeV/c in both kinematics." The level of agreement for the forward kinematics (Fig 9 top) is not great. One can certainly say that the "general trends are reproduced by the calculation.

9. Inconsistent use of selection cuts.
Discussion of regions of validity of the backward kinematics (lines 397-399) p>0.6 GeV, but the conclusion paragraph (line 441) uses p> 0.5 GeV/c. For consistency one should use the same values.