[Clascomment] OPT-IN:Beam-spin Asymmetries from Semi-inclusive Pion Electroproduction

[Luciano Pappalardo]

Dear Authors, 

thanks for this very interesting and well written draft.
Below some (minor) comments/suggestions:

Abstract: line 7: "intermediate Q2" is too generic (relative to what?). Skip "intermediate"

line 11: "insight into nucleon structure" -> "insight into THE nucleon structure"

line 32: "longitudinal momentum distribution and the TRANSVERSE positions of the partons"

line 41: "to probe THE nucleon structure"

lines 45-46: put "when a final... lepton" within commas 

eq.(2): add a comma after the equation

lines 75-102: Here I would modify the order of the various paragraphs to improve the logic flow" and eliminate some redundancies. For instance, the discussion on the "twist" is started in lines 79-80, defined rigorously in lines 88-96 (after a short paragraph discussing other things), with a dedicated and relatively-long and technical paragraph that distracts the reader from the main discussion, and then re-used in 96-101. 
I propose the following ordering:
- start with lines 75-80: "The current ... fragmentation functions [10,11]" 
- put lines 88-96 "The technical... O(M/Q)." in a footnote, attached to "twist-2 and twist-3" in line 79-80.
- continue with lines 97-100: "The twist-2 ... <qQq>." (this part matches naturally after line 80).
- continue with lines 80-86: "The helicity dependence ... structure function F_LU^sin(phi)" (here you introduce the structure function F_LU^sin(phi), then move to line 102, where you start describing it).
- eliminate the sentence 87-88 "The structure... in the proton" as redundant with lines 77-78.
- eliminate lines 100-101 "F_LU^sin(phi) intrinsically ... order 3" (out of context here, better to attach this part in line 102, see next comment).
- line 102: "The structure function F_LU^sin(phi) IS A TWIST-3 OBJECT AND in composed..."

eq. (3): add full stop after the formula.

line 101: "the leading order" -> "a leading order". It is not the only one ("the"), since also the Sivers function is also leading order and T-odd. Maybe, it is better to use "naive time-reversal odd" rather than "time reversal odd".

line 128: "asymmetry TO be zero"

line 153: Add "where X denotes the undetected final-state hadrons"

line 193: "instituted" -> "applied"

lines 200-203: don't have to explain in the paper what the Cherenkov effect is. Skip.

eq.(4): put comma after formula

eq.(5): put comma after formula

eq.(6): put full stop after formula (and eliminate full stop from "Eq.6." in 314).

line 326: Avoid beginning a sentence with a symbol (z). -> "THE VARIABLE z is..."

eq.(7): put full stop after formula (and eliminate full stop from "polarization" in 349).

line 358: "other results" -> "other kinematic dependencies" 

Figs. 11 & 12: use a larger font for the axis labels.

eq.(10): Out of context at the end of the paragraph. Should be anticipated right after "chi2 istogram." in line 398 and terminated with a full stop.

406: "the analytical technics" is too generic without further specification. At least add "(see details in sub-paragraphs below)".

419: "E_inner" Use a smaller font for subscript "inner". also in 434, 435 and 441.

eq.(11): put full stop after formula (and eliminate full stop from "Eq.6." in 314).

Fig. 14: The y-axis label "BSA" is barely visible and overlapping with the numbers. 

lines 548-549: add citations to papers after "CLAS" and "HERMES".

Fig.15: I would add two vertical dashed lines (e.g. in light grey) in the z panels in correspondence to z=0.4 and z=0.7 to better visualize the integration region for the other projections. 

608: add "(though the predicted magnitude for pi- is much larger than the present data)" after "for pi-".

Fig. 17: Add references to the CLAS and HERMEs paper in the fugure caption.


Best regards, 
Luciano