[Gdh_lowq2] comments on your ND3 analysis notes

[Jian-Ping Chen]

Hi, Xiaochao and Sebastian,

A comment on 15ND3: The additional neutron in N15 makes dilution worse, 
but it does reduce the polarized background, since the extra neutron in 
14N is now paired, leaving only one proton could be polarized.

Best regards.

Jian-ping

On 2/8/17 5:41 PM, kuhn wrote:
> Hi Xiaochao,
>
> If I may, just a few responses to some of your comments:
>> On Feb 8, 2017, at 4:55 PM, Xiaochao Zheng <xiaochao at jlab.org
>> <mailto:xiaochao at jlab.org>> wrote:
>>
>> Hi Krishna:
>>
>> I finished reading your analysis notes. I have the following comments,
>> divided into two groups. The first type of comments are a little more
>> "substantial" and may be relevant to others involved in the analysis,
>> and some are just for my understanding. The second type are "finicky"
>> details that others can safely ignore.
>>
>> First type:
>> a) I thought for the deuteron we used 14ND3?  What's the reason to use
>> 15ND3?  The extra proton can only add to the background of the D
>> measurement.
>
> It may have been a bad choice, but I’m pretty sure it was 15N (Alexandre
> can confirm). We only switched to 14N for eg1-dvcs.
>>
>> b) In addition to lattice and XPT, can Stan Brosky's light-front model
>> predictions for any of the moments measured?  I was at his talk last
>> week at the GHP workshop and it looks like his model can calculate
>> many things. (One interesting thing he mentioned was that the whole
>> nucleon spin is from quark OAM in his model.)
>
> There is no place in an analysis note to speculate on new model
> predictions. We could add a curve to the (eventual) publication if
> Brodsky can make one available. However, remember we are firmly in the
> “hadronic dof” region, where light front, AdS/CFTh and even “the spin
> carried by quarks” is largely irrelevant.
>>
>> f) same line, I think you are missing Delta E' which is the detector's
>> momentum acceptance in Eq.(3.1), or maybe Edetector contains it (but
>> see above comment e). Otherwise how do you get the dsigma/dOmegadE’?
>
> Out analysis method does not actually ever go over the step of
> calculating differential cross sections. We only look at the yield in a
> kinematic bin and relate that to the value of structure functions at the
> center of that bin.
>>
>> i) line 544: Etot/p is about 0.25 for electrons. Why is that? I
>> thought CLAS EC is a total absorption calorimeter which means this
>> ratio should be 1, unless if Etot is defined not in GeV?
>
> This is purely a convention which I’m sure the Analysis Review committee
> will understand. 0.25 is the sampling fraction of the calorimeter - so
> Etot is not the actual energy deposited in the whole calorimeter, but
> only the VISIBLE part of that (in the scintillators).
>>
>> j) Fig.3.5: What are the two peaks other than the MIP? And why are
>> they there?  And why did they become only one peak at 0.25 in all
>> panels in Fig.3.6? They appear to be exactly the same data.
>>
> Fig. 3.5 is just the sum of the panels in Fig. 3.6. As you can see, the
> maximum for real electrons is kinematic (Q2) dependent, and weighted by
> the relative contribution from these different kinematics it LOOKS as if
> there are 2 peaks.
>
>> l) line 996-997: If I remember correctly, the use of tau for
>> theta><pi/4 did not make sense. Is that true?  I think nobody knew why
>> these are used besides that they were in the code used by all previous
>> experiment (???)
>>
> Yes, you’re right: In practice we have (nearly) no events above 45
> degrees (pi/4), so the 2nd part is never needed. However, it’s correct
> “in principle” since at large enough scattering angles, the electron
> exits the target cell on its sides, and therefore doesn’t travel through
> the whole length.
>
>> m) line 1057 the error in the CC efficiency: I recall we had an
>> extensive discussion on how to evaluate the error on N2/N1 if N2 is a
>> subset of N1,
>> see https://www.jlab.org/Hall-B/secure/eg4/xiaochao/index_pion.html#04092009
>>
>> I have not found a solid proof in textbooks. So I think it will be
>> useful if you can add an Appendix to prove the formula used.
>
> I would prefer to leave it without formal proof - if the analysis review
> committee complains, we can supply the proof afterwards.
>
>> n) Eq.(4.3) I don't know why the normalization sigma_tot is on the
>> RHS. The cross section in the simulated N is what you need, right? So
>> it shoudn't be there (otherwise you take th ephysics out).
>>
>> Even if it should be there, which you have to explain to me why,
>> shouldn't it be sigma_tot-plus/minus?
>
> Sigma_tot^plus is the cross section integrated over the table for
> positive cross section differences only, Sigma_tot^minus the same for
> the cross section differences that are negative. Eq. 4.3 only takes care
> of any mismatch between the number of simulated events for these 2 cases
> with the number that SHOULD be simulated (which SHOULD be proportional
> to those respective cross sections).
>
> Hope this makes some sense. - Sebastian
>
>
>
>
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