[Clascomment] OPT-IN: First multidimensional, high precision measurements of semi-inclusive pi+ beam single spin asymmetries from the proton over a wide range of kinematics

[Stepan Stepanyan]

- p1, left column, no references are provided in the first paragraph for PDF, 3-D imaging (e.g. remarkable theoretical advances), or TMDs
- p1, left column, excessive referencing, 22, for spin asymmetry
- p1, right column, 2nd paragraph, description of Fig.1 must come after the description of the kinematic variables  
- p2, left column, should it be more explicit what cross-section? e.g. “is the differential cross-section of $\pi^+$ electroproduction for each …"
- p2, left column, 4th line below Eq.(1), should be “the longitudinally polarized (L) or unpolarized (U)” 
- p2, right column, the sentence that starts on line 4, “Apart from …” talks about “additional sources” that have been studied through model calculations. The next sentence starts with “This mechanism …”, which mechanism this statement refers to. 
I propose to consolidate these two sentences - “Apart from above two, a mechanism involving the poorly known twist-3 TMD distributions function $g^\perp$ can also give rise to the bam SSA. The $g^\perp$ appears in the decomposition of the quark correlator if the dependence on the light-cone vector is included."
- p2, right column, the last sentence, too strong statement - 3 possible mechanisms that contribute to the beam SSA have been listed, one of which is related to quark transverse motion. How then beam SSA can be a unique opportunity to unravel the role of quark spin-orbit correlations? Are all 3 mechanisms come from spin-orbit correlations?
- p2, right column, 2nd paragraph, description of CLAS12 is incorrect. Maybe we do not need to mention the central detector here since it is not used in this analysis, but it still wrong to say that the CLAS12 detector consists of six identical sectors. It will be correct to say “The CLAS12 forward detector consists of six …”. We have that description on the CLAS12 NIM 
- do we need to define Q2, W, y, xB …  
- p3, left column, 2nd paragraph, “number of counts …” what counts, it should be more explicit, e.g. “the number of $e^-\pi^+X$ events with …”
- p3, beam polarization Is quoted as 86.3+/-2.6%, the right form of writing will be 86.3% +/- 2.6%
- beam accidentals are missing from systematic uncertainties, there were no discussions in the analysis note as well. Was that ever studied?
- p3, fit to the \phi dependence of SSA, on the figure it shows a single parameter, looks like it was fitted with function f=p0*sin(\phi), it was not fitted by expression in Eq.(1), figure caption is incorrect 
- p4, seems to many model details that are not related directly to the comparison with the experimental data. some of the model descriptions get repeated. A bit cleaner, shorter discretions will help, in general, the text is hard to read. 
On page 2 there was a very strong statement about a unique opportunity to unravel the role of quark spin-orbit correlations. Should it be some statement of what we achieved in that regard with this multidimensional analysis?