[Clascomment] OPT-IN: Subthreshold photoproduction of phi mesons from deuterium

[Derek Branford]

Dear Wei,I have a few comments on your paper. Firstly let me say it is well written. As a native UK english speaker I find the english excellent. My comments as listed below are related to the science content.
Mid way down page 2 it is stated ....lead to a signal in the triple .... I think it would help the reader to give a few words on what this signal is - reduction in X-section, increase in X-section, resonance behavious, change in the angular distribution of outgoing particles,change in polarisation observables, or whatever. I think this would help as this is surely the main point of the letter. I see you give references and I would like to have checked them out but being retired living in Germany I do not have easy cost free access to PRC.
Fig 1. The y-axes are not labelled. Are these counts per **MeV bin, cross-sections, or what? I also think it would be useful to draw in the backgrounds used in these two examples.
Lower down you state ...checked to ensure ... t was in the physicsl region. It is not clear to me what is meant by this. Was t always in the \'physical region\'? If not - what did you do? etc. If you can say after checking then t was found to be always in the physical region then that would be a strong point. Otherwise maybe you have to give a bit more detail.
In the Breit Wigner formula the units of gamma (width) are MeV not MeV/c^2.
Page 2 para 2 The english goes a bit funny. Suggest .....the cross section on a hydrogen target was obtained using a fit to the g11 data of the form:
Equation 2 t\' is neither in the equation nor defined. tsub0 is also not defined.
Lower down you talk about the phi - N cross section. I am not sure what you mean here - scattering cross secton, phi+N->X, total absorption X-section or whatever.
Fig 2. Why is the last data point without an error bar?
Page 4 near the bottom. I would remove the word toy which I know is favoured by our Russian colleagues but it irritates me. \'simple model\' is ok to me.
I disagree with the conclusions. The results are not in agreement with the predictions of the simple quasifree model predictions. Of the three points two differ by around 2 standard deviations. The probability of this happening by chance is 1 in 400. This needs a bit more discussion. Could it be that there is already some evidence in the data of phi-N bound state!!!? A conclusion like \'the results are of the same order of magnitude as the calculation\' would be more acceptable to me.
Best Wishes, Derek