[Clascomment] OPT-IN: Measurement of the neutron F2 structure function via spectator tagging

[Reinhard Schumacher]

Hello Nathan and Other Collaborators,

I have read your draft paper "Measurement of neutron F2 structure
functions via spectator tagging", dated August 8 2011, with interest.
It is a well-written paper that gets its points across quite well.
Congratulations on getting the BONUS system results to the publicatin
stage!


Here are my questions and suggestions:

page 1 top of second column: You toss in a line about "critical input
for interpreting incluidive polarization asymm. measurements".  It is
not clear why this is the case.  Can you explain this claim, or at
least add a reference?

Equation 1: as a reader I don't want to have to guess: what is that
strange notation in the denominantor of the left hand side?  Is the
expression differential in the quantity (ps/Es) of the spectator?
That is, is it differnetial in the *speed* of the spectator?  That
ought to be clarified, either in the notation of the equation of in
the text.

page 2, middle of the left hand column: you introduce the spectator
angle selection criterion of 100 degrees.  Why this angle?  Why not,
say, 90 degrees?  I don't want to look up reference 13 to find out.
Can you add a statement about how sensitive the result is to this cut?

page 2, near the bottom of the left column and elsewhere: you keep
referring to momenta in units of MeV instead of MeV/c.  Personally, I
find this an annoying affectation ("we set c=1, so we don't have to
mention it"), and out of step with many dozens of CLAS papers where we
use MeV/c for momenta.  I recommend switching to the other form.

page 3 near bottom of left column: you may want "...approximation Eq
(2), the ratio..." for clarity.

page 4, right column near the top: you state that the W* region near
1.6 GeV is dominated by the F15 resonance.  Is that really the case?
How do you know that in the case of the neutron?  Does it follow from
the global anaysis that you refer to?  Another sentence or two would
make this more clear.

page 4, right column near the bottom: Well, the bump you show near
x=0.6 is certainly an intriguing observation.  You seem happy to blame
it on a specific resonance.  But I don't understand why a resonance
that is stronger on the neutron than on the proton should show up *at
a specific value of x*.  What does that even mean, physically?  I
think this needs some more discussion to make the case.

That's all for now, looking forward to your reply!

Sincerely,
Reinhard