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

[Mikhail Osipenko]

Dear Authors of BSA paper,

the results presented in the paper are very interesting, but I noticed a number of issues which have to be explained better. These are listed below.

Best Regards,
              Mikhail.

line 53 - z in parton model, I guess, is a fraction of struck quark momentum (at least in e+e-),
line 55 - momentum transverse with respect to what?
lines 88-96 - explanation of what is the "twist" seems to be wrong/incomplete/unnecessary (to me), I would suggest to omit it,
line 100 - F_LU has twist >=3 (the expression you give is the leading twist piece),
line 110 - do you mean "leading twist"?
line 113 - Silvers function undefined (or referenced),
line 120 - H^\perp_1 - is it twist-3?
lines 123-128 - does not seem to be useful/necessary,
line 208 - why "other cuts" applied only when N_phe<2.5?
line 218 - "region" undefined at this point,
line 223 - what do you mean under "energy" in the sampling fraction definition?
line 230 - why to cut above EC/p=0.3 peak?
lines 275-279 - does it make sense without electron fiducial cuts?
Fig.7 - does it make sense to cut below pi+ peak? Are you using log-Z scale?
line 287, Fig.8 - what do you mean under "momentum of EC hit"? Is it the total energy reconstructed in EC?
line 291 - does "start time" require also the knowledge of electron timing or RF is sufficient?
line 300 - not clear what have you done for the case N_gamma>2? Please explain.
line 338 - is it safe to take Delta resonance as the "Deep Inelastic Scattering"?
Eq.7 - you have probably checked that the Faraday Cup charge or number of inclusive events are the same for the two helicity states? Please add and quote precision of the check.
Eq.9 - what is the sensitivity to parameters B and C? How chi^2 in Fig.13 changes if you use only parameter A?
lines 376-401 - I am not sure you provided the number of phi-bins you are fitting here. Have you investigated why the fit does not work in the removed points?
Table I - I am not sure to find "Missing mass cut" systematic uncertainty description in the text?
lines 500-531, subsection D - what is the message of this section? The Eq.15 seems to be trivial, I am not sure you need to make simulations to demonstrate it? Am I missing something? Instead you probably could elaborate how did you check that your observables were stable over a long run time.