[Clascomment] OPT-IN:Di erential cross sections and spin density matrix elements for the reaction gamma p --> phi p

[Michel Garçon]

Dear Curtis,

Very nice results, and a nicely written paper. I have comments concerning syst. uncertainties, previously published CLAS data and some detailed editing corrections.

- systematic uncertainties: should not Table I make the distinction between overall normalization uncertainty and point-to-point syst. uncertainties? 
And what about syst. uncertainties in the SDME ?

- Anciant et al.: the difference of about 30% is slighly beyond the systematic uncertainties for both experiments. I am not sure this is worth mentioning. I agree with the statement that the present results supersede the older ones, but not "suppress" (Fig. 18 caption). And I am not sure that the chief motivation for the early experiment was to investigate the u-channel per say (as stated page 19), but to look for the manifestation of 2-gluon exchange.

- You omit to quote/discuss previous CLAS results on SDME: Phys. Rev. C 69 (2004) 032203 (R). Is this a genuine omission or else ?? In that paper rho_00^0 (in the helicity frame)is found compatible with 0 at small to moderate t, and it is then stated that SCHC seems to hold. How can we reconcile this with the present results? For a meaningful comparison (at this stage, I am not suggesting to include it in the paper, but I'd like to see it), could you plot your E=3.6 GeV rho_00^0 in the helicity frame as a function of t ?
The sentence p12c1 "The information (on SDME) was essentially non-existent..." is misleading.

- you use the notation tmin in page 1 and then later t0. Choose one of the two.

- p1c1: "200 MeV energy bins". MeV should not be in math mode.

- p1c2: "at near threshold and forward angles" -> "near threshold and at forward angles".

- p3c2: check sentence "To address the pion contamination, apply ..." (no subject).

- p4c1: "depend of sqrt(s), as well as ON the masses..."

- p4c2 last line: "Further details .... ARE given..."

- p5c2: "375 MeV/c". MeV/c (or is it only MeV ?) should not be in math mode.

- p10c2: I would write "Kloet et al. HAVE shown..."

- Fig.10: are you really confident with the first bin at 1.975 GeV which has a very distinct behaviour from the following ones ? This may also apply to the SDME's at that energy, but it is less striking.

- Fig. 15 caption: "2003" appears twice.

- p19c1: "much WIDER kinematic coverage"

- Fig. 20-22 captions: the sentence "The spin density ..." has no verb. Also should not it apply to Fig. 21 only? And in Fig. 21-22, should not you replace the information already given in Fig. 20 caption by "See Fig. 20 caption for ..." ?

- p26c1l4: you cannot have t->t0 with t negative and t0 positive. Also t0 was already defined p19c1.

- p26c1: "beta(t)" useless since it does nto appear in the formula.

- p26c1 remove the parantheses in B_phi(|...|), 2 occurences.

- p27c1l3: superscript 0 omitted.

- p27c1: "...converted INTO the Helicity...".


Best regards,
Michel Garçon.