OPT-IN: Search for the Ï1(1600) exotic meson and the first observation of the a1(1260) meson in the photoproduction reaction γp -> Ï+Ï+Ï-n

[Daniel Carman]

Dear Aristeidis, Paul, et al.,

I have read through the draft of your 3pi photoproduction paper include my comments
below. This was a very well constructed paper and was easy for me to read and understand.
Nice work. If you have any questions, let me know.

Regards,
Daniel
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Page 1:
 - Abstract. Line 4. Use "liquid-hydrogen".

Page 2:
 - Line 9. Use "... $P$ is the parity, and ...".
 - Line 11. Use "... and the antiquark and $S$ is ...".
 - Line 13. Use "Quantum Chromodynamics".
 - Line 17. Problem with opening quotation marks. (They should look like 66 and not 99.)
 - Line 24. Awkward. I suggest "... into an $S$-wave and a $P$-wave meson, such ...".
 - Line 25. Use "... the two $S$-wave meson decay mode ...".
 - Line 28. Use "Collaborations".
 - Line 28. You mention results from E852, VES, and COMPASS and then provide references
   [4-12], but without the Collaborations listed in the references, I cannot tell which data comes
   from which experiment. I recommend that for all references in the bibliography, you also provide
   the name of the Collaboration. (e.g. M. Nozar {\it et al.} {\it (CLAS Collaboration}), Phys. Rev. Lett. ...)

Page 3:
 - Line 39. Typo on "performed".
 - Line 41. Be consistent with style and give the reaction as "\gamma p \to \pi^+\pi^+\pi^- n".
 - Line 45. I suggest "... lack of the phase information for the partial waves.".
 - Line 48. Use "circularly polarized" (no hyphenation should be used if the first word ends in "ly").
 - Line 51. Use "beamline".
 - Line 52. Solid angle is not measured in radians. You can say that each sector spanned 30 degrees
   (pi/3 radians) or covered 2pi/3 sr.
 - Line 55. Use "... time-of-flight system, a gas Cherenkov ...".
 - Line 57. Use "liquid-hydrogen".
 - Line 59. Use "... therefore, to optimize ...".

Page 4:
 - Eq.(2) should end with a comma for proper punctuation.
 - Line 80. Use "... for both the ...".
 - Line 83. You should also mention the K^0_s peak in Fig. 1b.
 - Line 88. Use "... over the two positive ...".
 - Line 90. I suggest "... through a GEANT simulation ...".

Page 5:
 - Line 101. Here you give a mass region value of 1.38 GeV, but Fig. 1 uses 1.5 GeV. Shouldn't Fig. 1 use the same
   cut-off for the low-mass and high-mass regions?
 - Line 111. Use "circularly polarized".

Page 6:
 - Line 113. The sentence "The goodness of fit was verified by comparing the experimentally observed angular
   and mass distributions with the predicted ones." is far too qualitative of a statement and provides very little
   to the reader to understand the quality of the fit. Why aren't you giving a reduced chisq value?
 - Line 115. For the predicted data distributions, you state that you used a weighting given by "A spin-density
   matrix found A PWA fit". This is quite vague. What PWA fit are you talking about? The fits done for this paper
   or some other fit? The language used here needs some attention.
 - Line 118. Use "... are presented in Fig. 2.".
 - Line 129. Use "mass-dependent fit".

Page 7:
 - Fig. 2 caption. Line 2. Use "Breit-Wigner fits". Line 5. Use "mass-dependent fits".
 - Line 142. I prefer "... of a non-resonant exotic wave."

Page 8:
 - Fig. 3 caption.
   - Line 2. Use "mass-dependent fit" and "... is shown by the curve.".
   - Line 4. Use "... for the two $M^\epsilon ..." and "... against a resonant $\pi_2 ...".
   - Line 5. Use "... of a non-resonant exotic ...".
   - Line 6. Use "... a resonant $\pi_1 ...".
   - Line 7. Use "... and a resonant $\pi_1 ...".
 - Line 143. Use "... with the parameters reported ...".
 - Line 144. Use "For the long-dashed ...".
 - Line 145. Use "... mode [9], where the ...".

Page 9:
 - Line 152. Use "... are shown in Figs. 4b,c.".
 - Line 157. Use "... $\pi_2(1670), and ...".

References
 - All references should end with a period.
 - [3] should be: P. R. Page, E. S. Swanson, and A. P. Szczepaniak, ...".
 - As mentioned above, please include Collaboration names associated with all of the different publications.
 - [18]. Use "JLab". Also I would suggest that instead of referencing the proposal PR04-005, you list the
   approved experiment number and give the title of the experiment as listed in the proposal.