[Clascomment] OPT-IN: First Observation of the Line Shape of the Lambda(1405) in Electroproduction

[Daniel Carman]

						May 31, 2013


Dear Haiyun et al.,

I have read through your paper on the Lambda(1405) line shape study from the e1f dataset
and my comments are included below. I find, in general, this has the potential to be an
interesting result, but that the paper just does not include enough details to fully
satisfy me. I include all of my comments below based on the paper draft dated May 29. If 
you have any questions, let me know.

				Regards,

				  Daniel

********************************************************************
General.
 - Please use "$Q^2$" (math mode) throughout. Most of the time you use "Q$^2$".

Page 2.
 Left column.
  - Fig. 1. Decay proton of Sigma+ should be in italic font.
  - Line 56. As written, it is not clear what Ref.[12] is for. It is not a reference for
    the e1f dataset or for JLab. It is for CLAS. I suggest "... analyzed data from the e1f
    run in Hall B at Jefferson Lab collected using the CLAS spectrometer [12].".
  - Line 62. Use "$p$".
  - Line 69-71. These cuts seem arbitrary as written. Are the 3 sigma cuts, 4 sigma cuts?
 Right column.
  - Fig. 2. I don't think that you should show unphysical portions of the mass ranges, especially
    as you don't explain what is going on. I would plot this figure with an x-range from 1 to 1.4
    and an y-range from 0 to 0.4. Likely a logz scale would be appropriate and an overlay of your
    nominal cut limits.
  - Line 82. You make a very strong statement about what you believe the background in your
    data sample is. However, you never mention particle misidentification, especially the
    misidentification of K+ as pi+ or protons. Certainly multi-pion reactions have an important
    contribution to your spectra that needs to be understood.
 
Page 3.
 Left column.
  - Fig. 3 caption. Use "Two range of $Q^2$ are shown.".
  - Line 107. Use "The acceptance correction was performed ...".
  - Line 110. Use "... space of the independent kinematic ...".
  Right column.
  - Fig. 4 caption. Use "... mass squared ...".
  - Fig. 4. Clearly your data is shifted from your Monte Carlo peak. Thus something in the data
    or Monte Carlo is not understood. Have you properly included energy loss in the target in 
    your simulation or other effects that could cause this disagreement?
 
Page 4.
 Left column.
 - Fig. 6. I am not convinced that there is any real statistical difference between the data shown
   in (a) and in (b). Thus I am quite nervous about strong claims of differences between the
   distributions. Also, I would be curious about what portions of CLAS are probed for your different
   kinematic ranges. Have you taken care to define appropriate fiducial cuts to limit your sample
   to highly efficient regions of the CC? Have you accounted for the CC efficiency function? Have
   you studied the impact of your acceptance on the rather strong tracking and trigger inefficiencies?
 - Fig. 6 caption. Use "Two range of $Q^2$ are shown.".
 - Line 120. I am not sure what you mean by "The dependence on this phi distribution was studied
   and the systematic uncertainties were obtained." Are you referring to the systematic associated
   with a phase space phi distribution and one where you tailor the MC to match the data? If so,
   I think this statement could be more crisply made here.
 - Line 123. Use "$W$".
 - Line 127. What do the acceptance corrections look like? What is the typical acceptance and the
   range over your kinematics? What are the statistical uncertainties on the acceptance function?
   Are they included in the error bars of Fig. 6? I think that given the level of importance of
   this correction to your spectra, that you could say a bit more about it. 
 Right column.
 - Fig. 7. I do not understand the "fits" of Fig. 7(a) or (b). The red curve could well match the
   data above MM=1.38 GeV if it were scaled by ~0.8. Something seems strange here. More detail is
   needed. 
 
Page 5.
 Left column.
  - Line 136. Use "... value of the ...".
  - Line 149. You state "The systematic uncertainties should be independent of statistics and
    change slowly between nearby bins." Just because they should, doesn't mean they are. In fact,
    it is a well known issue that in low statistics experiments, it is very difficult to cleanly
    separate systematic effects from statistical effects. Whenever this issue has been studied,
    a clear correlation is seen between the two.
  - Line 151. This smoothing process that you mention here is dropped in passing, but it sounds
    potentially worrisome without at least some level of details. What are you smoothing? What
    are you using as a guide that what you are doing makes any sense?
  - Line 156. Use "... around the $\Sigma^+$ ...".
  - Line 157. Use "... around the $\pi^0$.".
  - Line 158. The statement "The resulting variations were smoothed by fitting the relative
    uncertainties to a customized function." does not tell me too much and raises worrisome
    questions. What variations are you referring to? What relative uncertainties are you referring to?
    What is your procedure? What is your customized function?
 Right column.
  - Line 181. You make a statement that radiative corrections are not important and can be
    neglected. What studies did you do to determine that radiative effects did not affect the
    line shapes?
 
Page 7.
 Left column.
  - Line 243. You make the statement "Thus, we conclude that the whole of the measured background-
    subtracted distribution below the Lambda(1520) is due to the so-called Lambda(1405).". Again,
    what are the contributions from kaon mis-identification due to multi-pion final states? 
 Right column.
  - Line 249. Use "line shape".
 
Page 8.
 Right column.
  - Line 302. Use "B.A. Mecking".