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

[Stepan Stepanyan]

The $\sin{\phi} moment of the semi-inclusive deep inelastic scattering (SIDIS) cross section of a polarized lepton from an unpolarized target, $A^{\sin{\phi}}_{LU}$, has been extracted from measurements of beam-spin asymmetries (BSAs) in pion electro-production". Data were taken with the Large Acceptance Spectrometer (CLAS) of the continuous electron beam accelerator facility (CEBAF) at Jeerson Lab using a 5.498 GeV longitudinally polarized electron beam and an unpolarized liquid hydrogen target. All three pion channels ($\pi^+$, $\pi^0$, and $\pi^+$) have been measured simultaneously over a large range of kinematics for photon virtualities up $Q^2\sim~4.5$ GeV$^2$. The moment is measured as a function of z, $P_T$, $x_B$, and $Q^2$. The $A^{\sin{\phi}}_{LU}$ is a twist-3 structure function and provides information on quark-gluon correlations. This new high statistical data will provide an important means of studying the transverse momentum of quarks in the nucleon.

General comment - Figures are very low quality, in many cases labels run over axis values, there is no
consistency in labeling asymmetry graphs, there are labels "A", "BSA" and also "$A^{\sin{\phi}}_{LU}$.
 
Introduction
p1, line 16 - is it true that gluon contribution is ~30%? at least papers cited have \Delta G ~0
p1, line 32 - perhaps it should be "the TRANSVERSE position ..."
p1, line 33 - sentence that starts on that line, better to say "GPDs and TMDs are connected through
the Wigner distribution functions or Generalized Transverse Momentum Distributions (GTMDs) and
provide complete description of the three-dimensional structure of the nucleon."
p1, line 38 - confusing sentence, better to say "Measurements of azimuthal moments, in particular  
the single spin asymmetries (SSAs) have emerged recently as a powerful tool to probe nucleon structure
through measurements of GPDs and TMDs in hard exclusive and semi-inclusive electro-production of mesons
and photon, respectively."
p1, line 47 - phrase "the TMD partonic distributions" foes not sound well, may be "the TMD of partons".
p1, Eq. (1) - I assume "x" is Bjorken x, it is better to have it $x_B$ to not confuse with internal x for GPDs. This
must be corrected throughout the text
p2, line 75 - better to start "The presented measurement is for the third moment of the above cross-section,
$A^{\sin{\phi}}_{LU}$, the ..."
p2, line 93 - I believe it should be "the ratio M/Q" and not "ration"
p2, line 94 - I am not sure the sentence "Hence ..." is correct. Why you need "Hence", do you want to say
"The twist-2 is called leading twist while twist-3 is subleading twist because it is suppressed by $O(M/Q)$".
Experiment
p3, line 150 - consistent with beam energy value, in the abstract it is 5.498 GeV, not a big difference but it is
better to be consistent
p3, lines 172-173 - statistical uncertainty in the Moller measurements has no value, 0.2% does not represent
error of polarization in any way. Error on polarization measurement comes from systematic sources and for
Hall-B Moller polarimeter it is ~4% 
p4, line 217 - EC trigger discriminator does not have sharp cut on energy. Due to non-uniformity of energy
collection, the set threshold cuts wide range (~20-30%) around mean value depending where the hit acquired . So, quoting 3-digits value of energy cut by discriminator threshold, 0.639 GeV, is miss leading, it is better to say ~0.6 GeV
p4, line 265 to 266 - definition of the \Delta t is incorrect, difference between these two times will not be =0, unless
you subtract event start time that is calculated from electron
p4, Eq.4 is incorrect, Time=Distance/Velocity, Velocity=beta*c, and beta=p/sqrt(p^2+m^2), so the equation
should be: Time=Distance*sqrt(p^2+m^2)/(c*p)
p4, line 271 - better to say "is the path length of the track from the production vertex to the time-of-flight plane"
p4, line 274 - end of the sentence, remove "and tracks"
p5, line 300 - Question, you are selecting events with 2 or more photons, when you have more than two, how you
analyze invariant mass distribution, it is need to be explained. Can you show invariant mass distributions of two
photons for 3 or more photon final states
p6, line 318 - add "of the exchange photon" after "virtuality"
p6, line 325 - correct definition of x, first it better to write $x_B$, second it is not "fraction carried by the quark
in the hadron" it is the quark in the proton
p6, line 330 and 331 - better to say "with CLAS" instead of "in the CLAS"
p6, line 333 to 334 - phrase in parentheses can be omitted, it has been said before and there is no a single picture
showing the range Q2<1, so no need for new explanations
Data Analysis
p6, caption of FIG.10 - it is better not to use nomenclature "E1-f", you could just say "Kinematic coverage for SIDIS
event in resent experiment"
p6, line 353 - as commented above, there is no meaning in statistical uncertainty of beam polarization from the
Moller measurements. Eror on polarization is nominated by systematics and for Hall-B it is ~4%
p6, line 358 - what it means "to see other results" which other results are we taking about
Systematic Studies
Table I - (a) why electron EC cuts have different systematic uncertainty for different pion spices, (b) is this in %
or absolute value? (c) systematics for beam polarization should 4%
p8, line 490 to 492 - I am not sure where "this well know systematic effects come from", we know that we measure
3-4% difference in polarization with different target field orientation, and we know Hall-B moller measurements in
general few % lower than overall expectations. Non of these can be explained by "well know effects". The systematic
error on measured polarization is about 4%, so $\Delta A=0.04*A$ and if A~0.03 the systematic uncertainty on
A should be ~0.0012, at least facter 2 higher than is quoted in Table I
p9, line 529 - what is the relebance of FIG.14 with discussion with acceptance
P9, caption of FIG. 14 - better to say "plotted in red open symbols (blue solid symbols)"
Results
p9, line 533 - remove "successfully", it has no meaning
p9, line 553 - better to say "at small angles" instead of "low angles"
p10, FIG. 15 and 16 - why symbols have been changed for pion types between these two figures? It is hard to
see the definition of symbols on top of figures
p11, line 565 - HERMES does not operate any more, replace it with "Because of HERMES results were obtained at a
higher beam energy ..."
p11, line 567 - where this scaling factor comes from, can you give a reference
p11, line 584 - bad sentence, previously is used twice, replace with "There has been a phenomenological work
that attempted to extract twist-3 functions from the existing data [43], however higher precision data are needed
for model independent studies of TMDs [44-47]".
p11, line 588 - what are [48] and [49], it should be explicitly written on what current data give significant upgrade,
or improvement
p11, line 593 - better to say "In Fig.18 our results are compared ...", in general this is very long sentence, consider revising it
p11, line 595 - again referring to a citation as a object, better to say "... moment, where prescription from [46] is
used to model ...
p11, line 596 - continuation of the sentence is absolutely unclear after ", and " what means "and [23, 50], which .."
for what 23 and 50 have been used?
Conclusion
p11, line 625 - "The $\sin{\phi}$ moment of the SIDIS ..."
p11, line 627 - better to say "with good statistical accuracy"
p11, line 629 - better to say "published by the CLAS [48, 56, 57] and HERMES [49] collaborations"
p11, line 631 - better to say "a major improvements in statistical accuracy and kinematical coverage
p11, line 637 - instead of finishing sentence after "collaboration" juts continue " obtained with a different beam
energy and the modified detector configuration".  and remove rest of the sentence "so ...."