[Clascomment] OPT-IN:Single and double spin asymmetries for deeply virtual Compton scattering measured with CLAS and a longitudinally polarized proton target

[Silvia Niccolai]

Hello Volker,
Please let me give you a quick reply on the authors list question - and then we'll work on the rest of your comments in the upcoming days and send you a more complete reply (and update our paper accordingly). 

As you know, the eg1-dvcs analysis on DVCS is the outcome of years of analysis by a team formed by Erin, Silvia P., Angela and myself. Each of us brought various contributions to the project, and each of us participated on the same footing in defining all the stages of the analysis, but Erin and Silvia P. were the two people doing all of the actual data analyses: Erin focusing on the TSA, Silvia P. on all the three spin observables. We decided therefore to have the PRL with Erin lead author (as it is about the TSA) and the PRD with Silvia. For the rest of the authors, we made an agreement among the four of us about what sequences to adopt for the two publications. 
We decided recently, during the Ad Hoc review, to include Michel Guidal and Marco Mirazita among the lead authors of the long paper because they contributed to our results, each in a different way, even if they were not as involved as our analysis team was. 

If your question is somehow connected to the ongoing discussion about Hyon-Suk's draft author list, I don't think we have to necessarily adopt the same conventions depending on the final state that is published. What matters is what is done in the run group, in my opinion. E1-dvcs has maybe his own "traditions" (even if for Ivan's paper we used a different lead authors' scheme than for FX's), but things are apparently different in eg1-dvcs. For Yelena's paper, for instance, the people of the run group (spokespersons as well) were not included as "second-level" lead authors. So we consider that we can do the same for our paper. Moreover, we think that our author list reflects the actual contribution of people to this work, while a purely alphabetic one wouldn't. 
While we hope that this doesn't create problems, we would really like the list to stay as it is. 
Thank you very much and best regards.
Silvia

Best regards

Sent from my iPhone

> On 20 Dec 2014, at 22:36, Volker Burkert <burkert at jlab.org> wrote:
> 
> Dear Silvia Pisano and all,
> 
> This paper is the result of a very big effort, and it is great that we are converging 
> on this full paper. Here I have some, hopefully constructive, comments on some parts 
> of the paper that could be improved.  
> Volker
> 
> 
> General: 
> 
> 1)    You have many figures that include color. Unless you want to pay a lot of money to 
> have them included with color in the printed version, you should include Figure XX (color online) 
> for each Figure that includes color. 
> 
> 2)    Throughout the paper different use of units is made. For example, Q2, t, W is often used 
> with c=1, while in other places Q2, t have units (GeV/c)2 . Make it consistent throughout. 
> 
> 3)    If the current authors list should become the final “lead authorship” group, this would 
> establish a 4-tier ranking. If I include the ranking within the Orsay authors, it is even a 5-tier 
> ranking.  Unfortunately, the previous PRL has already started this, which broke with the 
> tradition from ALL previous DVCS paper to place the primary analyzer(s) first, and the 2nd 
> tier authors are the core discussion group listed in alphabetic order. If anyone believes one 
> is getting more credit or recognition for being in place “#3” compared to place “#5” they 
> are mistaken. 
> 
> Detailed comments: 
> 
> Eqn.(1): Instead of defining only Q2, it would be better to define all kinematics quantities 
> (Q2, ν, W, xB , ξ, t, p, p’) in one block of equations before describing the hard scattering 
> requirements. It becomes difficult to read if most of the definitions are squeezed into 
> the text. It also avoids using quantities such as “t” before they are defined (eqn.(2)), also 
> Fig.1 is referred to before quantities used in the figure are defined ξ, t. Also, in the notation 
> in Eqn.(1) Q2 will be <0, but in the figures later it is quoted as Q2>0. I suggest to use the 
> usual definition q2 = (e-e’)2 and Q2 = - q2.    
> 
> Line 132-135: 
> There is no reason to put down the Shifeng CLAS measurement as being of “limited statistics” 
> and “non-dedicated” while the Hermes data with even less statistics, and came 4 years (!) 
> later, are just referenced without qualification (as it should be). I consider our 2006 data 
> as pioneering results. 
> 
> Line 262:  the phrase “less than a meter’ should be replaced by the exact quantity as is done 
> for the other distances, e.g. is line 273 for the distance to the CLAS center.
> 
> Line 300:  “DVCS events” should be replaced with “epγ events” or “single photon events”.
> 
> Line 345: “..low-number-of-photoelectrons peak” should be replace with “single-photoelectron 
> peak”. [Note that the sharp peak in Fig. 5 is exactly at the one-photoelectron position.] 
> 
> Line 252-253: The momentum is actually measured by the drift chambers from their curved 
> trajectories in the Torus magnetic field.
> 
> Line 265-266: I don’t think these are neutrons. [Note the 2ns structure is visible in Fig. 8 as 
> sharp lines that are independent of energy. This indicates that these are out-of-time photons. 
> If they were neutrons, one would not see the 2nsec beam structure.] I suggest replace 
> “to separate the photons from neutrons” with “to select the in-time photons”.    
> 
> Line 410-413: There we argue that π0 were not included in the simulation to explain the 
> discrepancy with the MC simulation for EC. However the next section starts with the headline 
> “Exclusive π0 simulations”. A referee may ask why were they not included in the simulations 
> with the DVCS/BH events. 
> 
> Line 436: Why did the cut allow events with more than one photon if we include only single 
> photons in the asymmetries? That seems to increase π0 contamination that then will have 
> to be subtracted later.
> 
> Line 479:  “W” should be defined in Eqn(1). 
> 
> Line 487: “smearing” sound like it includes human (GPP) intervention, I suggest to use 
> “broadening” instead.
> 
> Line 498: “..these data appear to be strongly dominated…” replace with “..these data are 
> strongly dominated..” 
> 
> Line 500: replace “appear to be” with “are”. 
> 
> Line 505: replace “heavier” with “larger”. 
> 
> Line 583-585: “xB shows the strongest deviations from the constant behavior … but a
> constant fit is doable” Replace with something like this:  “There may be a small xB 
> dependence, although the dilution factor is not inconsistent with a constant behavior”.  
> [To better quantify this, a straight line should be fit to the data. The slope may not deviate 
> by more than 1.5sigma from a zero slope.] 
> 
> Figure 12: The MM2 distribution clearly peaks closer to the (pion mass)2 (~0.018) 
> than the photon mass (0). This should be mentioned and discussed as it already 
> shows that π0’s dominate the “epγ” sample in EC. This is still true after all the exclusivity 
> cuts. [In line 436 it is discussed that event were selected with “at least one photon”. 
> The question I have is, do the exclusivity cuts include a single photon only constraint 
> or not, and if not, why not? ]
> 
> Figure: 13: The thin black lines showing the binning should be made thicker, in the top graph
> they are hardly visible. 
> 
> Line 713 and Fig.17. The carbon (red) data show a shift towards more positive values of ALU, 
> which may indicate a bias in the carbon data. Two data sets to be comparable at the 3sigma level 
> does not indicate good agreement.  The more relevant comparison is to compare the leading 
> twist contributions, i.e. sinφ moments. I suggest to fit the two data sets with an offset fit parameter, 
> i.e. AUL=  a + bsinφ, and compare the b values for both data sets. My guess is that they would 
> agree better than the 3sigma quoted for the comparison of the unfitted data sets.  
> 
> Line 863-866 and Table IV: The table compares errors for the asymmetries BSA, TSA, DSA.  
> The quotation of relative errors is not a useful way of showing asymmetry uncertainties 
> as the asymmetry is already a relative quantity. The absolute asymmetry errors should be 
> given, e.g. AUL ± ΔAUL . The consequence of showing relative percentage is demonstrated 
> in lines 863-866, where one has to explain why the quoted (relative) errors are so different 
> for the different asymmetries while the absolute errors are basically the same. 
> 
> Line 949, 996, 1049: These definitions should be given in equation mode with an identifying 
> number, not squeezed in between the text. Also, these definitions are repeated in the captions 
> of Fig.18, Fig. 20, Fig. 23. If they are properly defined with numbers, they should be referenced 
> as such. 
> 
> Figures 18, 20, 23: The graphs include ultra thin lines showing the fits to the data. The lines 
> are nearly invisible. 
> 
> Line 1147-1152: The qualitative conclusion about “scaling” is insufficient. If we want to conclude 
> something about scaling, we should make it quantitative. The data should be analyzed with a 
> straight line a + bQ2 at fixed xB. The uncertainty in b would be the relevant quantity to conclude 
> about “scaling” behavior. Since we have only two points in Q2 at fixed values of xB a fit is not 
> required, just simple algebra.  I suggest to do this exercise.
> 
> Conclusion section: One should include something about improved analysis once the new 
> cross section and beam asymmetry  data are available. Also, the 12GeV DVCS program should 
> be referred to. 
> 
> Happy holidays! 
> Volker
> 
>