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

[Reinhard Schumacher]

Hello Dan,

	Below are the answers to the questions you asked about this paper.  We 
have posted a new version (v2) on the CLAS reviews web site.  A lot of 
small and not so small changes were made based on peoples' comments. 
Let us know if you have any other questions.

Sincerely,
Reinhard and Haiyun
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General.
  - Please use "$Q^2$" (math mode) throughout. Most of the time you use 
"Q$^2$".

Done.  Lots of Q's and t's were fixed.

Page 2.
  Left column.
   - Fig. 1. Decay proton of Sigma+ should be in italic font.

Corrected

   - 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].".

The sentence is changed.

   - Line 62. Use "$p$".

Corrected here and other places.

   - Line 69-71. These cuts seem arbitrary as written. Are the 3 sigma 
cuts, 4 sigma cuts?

They are 4 sigma cuts. (p.s. I (Haiyun) made a typo here, the pi0 cut 
range is from 0.05 to 0.25. Accordingly, the systematic study was cut 
from 0.06 to 0.24 instead of 0.04 to 0.19. This mistake was originally 
from a typo that I accidentally erased the 5 in 0.25 and it became 
inconsistent with the systematic study cut. Then I made another mistake 
that I thought the systematic study cut was a typo. Finally it ended up 
that neither of these two ranges is stated correctly in the draft.)


  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.

The range of the histogram is changed.  There should be no confusion now.

   - 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.

The possible multi-pion channel is pi+ p pi- pi0. These events are 
possible contamination only when the invariant mass of p pi0 is around 
the Sigma+ mass. These events can actually read out from Fig. 2. The 
events around Sigma+ in Fig. 2 are possibly coming from two sources: one 
is this multi-pion production, and the other is from the Sigma+ 
production smeared by detector resolution. The latter can be simulated 
and we showed the result of the simulation in analysis note. The 
comparison between them shows the contamination from multi-pion 
reactions are very small.

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 ...".

All these sentences are changed, as well as many others.

   Right column.
   - Fig. 4 caption. Use "... mass squared ...".

Caption is changed.

   - 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?

First of all, our simulation agrees with the data very well in general. 
All corrections are applied carefully. A series of histograms comparing 
simulation and data are shown in the analysis note. The result shows the 
simulation matches the data very well. Fig. 4 does show a very tiny 
difference of the peak position. This is from the form of the 
Breit-Wigner function we used to generate simulation events. A better 
function is the relativistic Breit-Wigner function, like we used to fit 
the line shape. The function we used on the K* simulation is a 
non-relativistic Breit-Wigner function. One of the differences between 
them is the apparent peak position with the same resonance parameters.

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?

We are not claiming that the two panels in Figure 6 are very different. 
  The caption states that the higher Q^2 region is the only one with 
some visible evidence for two bumps.  Following the advice of Brian 
Raue, we relaxed the fiducial cuts in the e1f data set in order to have 
statistics to see anything at all.  For the rest, we relied on the 
existing GSIM code.

  - Fig. 6 caption. Use "Two range of $Q^2$ are shown.".

Corrected.

  - 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.

Paper is updated with more clear explanation.

  - Line 123. Use "$W$".

Corrected here and many other places.

  - 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.

Acceptance correction is monotonically increasing from about 0.2% to 1% 
from the threshold to the Lambda(1520) region. It is very close to a 
straight line. The statistical uncertainties of the acceptance are small 
and included, of course, in the error bars of corrected yield.

  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.

The plots of the fit are updated. There was a mistake when the fit 
results were plotted on top of the data. To make a long story in short, 
RooFit package treats every function in a fit as a probability density 
function. This normalizes the integration of each function in a certain 
range to one. On the other way, the overall fit is normalized to the 
total yield of the data. This behavior can be changed but I forgot to do 
it. This didn't affect the good fits.

Page 5.
  Left column.
   - Line 136. Use "... value of the ...".

Corrected

   - 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.

A better explanation of the smoothing process is put in the text to make 
it more clear.  Two things: 1. systematic effects are indeed entangled 
with statistical effects; 2. systematic uncertainties are assumed to be 
smooth and statistical effects are fluctuating.
he mixed effects from systematics and statistics. The smoothing 
procedure is exactly the attempt to separate smooth systematic 
uncertainties from the fluctuating statistical fluctuations.

   - 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?

The guide is the assumption that the systematics are varying smoothly 
across bins. The smoothing process is designed reduce the effect of 
statistical fluctuation entangled in the systematic uncertainty.

   - 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?

The text is modified to reduce the confusion but remain focusing on the 
physics of the paper.

  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?

It already states in the paper that we did not make radiative 
corrections.  With the statistics we have it can hardly matter. The fits 
we make do include Breit-Wigner functions with a freely-floating width. 
  In principle, if the distribution gets stretched out a bit due to 
radiative effects, at our level of precision the fit should just 
accommodate it by increasing the width.   As you can see, there is no 
way we can be sensitive to finer details of the line shape.

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?

As replied before, kaon mis-identification is minimized and was found to 
be negligible in this analysis.

  Right column.
   - Line 249. Use "line shape".

Corrected.

Page 8.
  Right column.
   - Line 302. Use "B.A. Mecking".

Corrected.


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