[Clascomment] OPT-IN:Differential cross sections and recoil polarizations for the reaction gamma p --> K^+ Sigma^0

[Elton Smith]

Authors,

The paper overall reads very well. A few suggestions for improvement
follow:


abstract. Positive statement about SU(6) static quark model. At forward
angles we find that the P_Sigma is of the same magnitude, but
opposite sign, as P_Lambda in agreement with the static SU(6) quark model
precition of P_Sigma ~ -P_Lambda. This expectation is violated in some
mid- and backward-angle kinematic regimes, where P_Sigma and P_Lambda are
of similar magnitude but also same sign.

[See also comments below under \"recoil polarization\"]

Page 2, right column
Give tagged photon energy range. Could add to the end of first paragraph:
\"...were included in the trigger, resulting in a tagged photon energy
range of ... to .... GeV.\"

p. 4 fig 2
Black curves representing cuts are invisible, at least on the lower part
of the plot (b). Consider changing color to white or another light color.

p. 7 first paragraph under VI.
\"An additional momentum smearing algorith...\" A reference should back up
this statement, or at least the text should indicate the magnitude of the
corrections, or both.

p. 7 right column middle, suggestion, remove or move \"in the next step\"
\"For the three-track topology, we expand the...\"

p. 7 following Eq. 7
The spin projections must be defined in a specific coordinate system. Is
it the cm frame? Should be specified.

p. 7 same pagragraph, furhter down, suggestion, eliminate \"large-enough\"
\"...but we found that the (JP=1/2+-.....) set of waves was sufficient...\"

p. 9-10, B. Traditional method, comment
The discussion of steps for the 3-track events is clear, but I am left
with questions about the 2-track events. Admittedly, I have not checked
Appendis in Ref.14 in detail. Nevertheless, this document should add a few
more words of clarification. For use of Eq. 19 it seems like we need to be
in the Sigma rest frame, but how is this defined if the pi- is missing?
There must be more averaging than just \"the Sigma-Lambda spin transfer\"
and it would be useful to add a sentence or two of clarification.

p. 10, Eq. 18 and previous, missing Eq. number.
Previous Eq. is mising a number, although it is (incorrectly) referenced
as Eqs. 17 and 18 in the sentence preceeding numbered Eq. 18 in text.

p. 15, Fig. 11.
The LEPS data points are completely invisible. I suggest use of solid
black points, which are used for GRAAL data in Fig. 13.

p. 19, recoil polarization, comments, questions

1. Discussion of static quark model: I assume the SU(6) prediction comes
from assuming the Sigma and Lambda polarizations reflect the strange quark
polarization. If so, you might as well state this.
2. The equation P_Lambda ~ -P_Sigma is repeated several times in the
article. Since the paper is about the Sigma0, I suggest you reverse the
equation to read P_Sigma ~ -P_Lambda [i.e. P_Sigma is the \"unknown\"]
3. This discussion, as well as abstract seems to imply that there is a
kinematic region where the SU(6) expectation holds (to some high
accuracy). It might be useful to simply state that for s>2.2 GeV, the
Sigma and Lambda polarizations are equal to within 20%(?) and have
opposite `signs, as expected from the naive static SU(6) quark model.
4. Note that the statement that this expectation is valid for forward
angles needs to be qualified with a range of s. [See also left column p.
20.]

p. 20, left column, second sentence, remove \"On the other hand.
\"...separate fronts. These precision polarization....\"

p. 21, left column, last sentence before ack, polish. suggestion:
\"Additionally, all four analysis come from THE same data set and use
similar techniques, which will help control systematic uncertainties.\"

Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton at jlab.org
(757) 269-7625
(757) 269-6331 fax