[Eg6_analysis] eg6 meeting

[Eric VOUTIER]

Hello Mohammad, 

This is a pretty nice talk that you put together, I would have a few comments for your consideration 


Slide 2 : reachable --> measurable 
quark/anti-quark --> parton (it is not only qqbar but also gluons and you may prefer partons to be more strict) 
cleanest .... ---> DVCS is considered the easiest way to access GPDs (DVMP is not "dirty") 

Slide 3 : strictly speaking, GPDs are not a probabilities, you may call them overlap probabilities but this could be too technical 
Last sentence --> it is just the other way around = BSA is sensitive to DVCS 

Slide 4 : You should express C+ in the integral 
Add somewhere in the text "Compton Form Factor" 

Slide 6 : PR-08-024 --> E08-024 within JLab nomenclature, you may also add spokesperson names 

Slide 8 : yeild --> yield 
What about contamination from incoherent channels that would mimic a coherent reaction ? In other words 
can you put a probability number on the purity of your helium sample in the TPC ? 

Slide 9 : theoretical calculations are done at a fixed kinematical point in x, Q2 and t; you are missing the Q2 information 
for all the theoretical plots. Put a lot of caution in your wording since for a correct comparison to models you 
need to integrate the models over the experimental acceptance, especially in the case of this low statistics experiment. 
You are missing similar information for HERMES points 

Also, be aware for your presentation that comparing HERMES and CLAS in this t-dependent plot is 
somehow misleading since HERMES and CLAS are not measuring the same quantity just because not exploring the 
same xB Q2 phase space. 

Slide 10 : H_im and H_re are squared in the alpha_3 term (this is the DVCS^2 amplitude) 

alpha_1 is better of the order of 1, not 10 
"not sensitive to alpha_3" is something that you have to demonstrate and which is not showing up at this moment from your results 
Note that the real part can be about 10, so squared is 100 and times alpha_3 put it at the same order of alpha_2 

You may say that this analysis is not considering cos2phi dependence expected to be small magnitude but that you will investigate 
later how accurate is this approximation 

Slide 11 : globally same remarks for the comparison to HERMES and theoretical models + you are not showing any missing mass plot for the 
incoherent channel 

Slide 12 : you indeed seem to have a different trend but this may also come from basic re-interaction or final-state interaction effects like in 
(e,e'p) reactions 

Very nice job, 

Eric 








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