[Clascomment] OPT-IN: Hard Two-body Photodisintegration of 3He

[Lawrence Weinstein]

Why is this paper aimed at PRC rather than PRL?  This is the first observation of s^n scaling in a nucleus with A>2.  It should be possible to shorten the paper for PRL.

Overall, I think the paper is clear, well written, and describes important physics.

I have two physics comments: (1) RNA describes the data almost as well as scaling.  It is certainly not ruled out by the data.  This probably deserves more discussion. (2) The disagreement with Daphne and CLAS should be discussed in the text, not in a footnote.

- Larry

Here are some minor grammar, style and physics comments:

l1-3: change to: "where n_i and n_f are the total number of elementary fields in 
the initial and final states respectively that carry a finite fraction of the particle momentum"

l18 and many other instances: replace pQCD with $p$QCD

l31: add 'of' before 'modeling'

l32: delete 'a' before 'theory'

l46: delete 'Only'

l55: delete ',' after 'short'

l70: it is not clear what the 'it' refers to.  Perhaps break the sentence into two pieces: "We
chose to probe dimensional scaling in the reaction γ3He → pd in the energy range 0.4 -- 1.4 GeV.  In this energy range, photoreactions on the proton and the deuteron have shown signatures of scaling, but the interpretation of them is unclear."

l124: should you define CLAS?

l129: the 3He target was cryogenic.  Was it liquid or cold gas?

l153 (after the equation): Replace with "$\alpha$ is the light cone variable for each particle:" 

l154: "where $A=3$ is the mass number"

l177: add 'CLAS" before 'data'

l177: this paragraph can be greatly shortened of you want to aim for PRL

l197: what is the missing mass of the proton?  Is this the missing mass for the reaction g + 3He -> p + X?  If so, then say that explicitly.

Ref32 needs a number for the CLAS Note.  Is this an analysis note or a CLAS note?

l237-8: delete 'a' before 'high' and 'a' before "photodisintegration"

l244: replace 'not similar to' with 'different from'

lines 246-249: is it possible that the absence of resonance contributions is due to the fragility of the deuteron?  In other words, if a nucleon is excited to a resonance and then deexcites via meson exchange, the exchanged meson will almost certainly break up the deuteron.  

l246: define 'resonance region'.  I assume you mean W < 2 (where W is defined assuming a nucleon target).

l248: add 'nucleon' before 'resonance'

l274: delete 'as a dashed line'

l274: add some comment about whether the RNA describes the data or is ruled out by the data.  I do not think that it is ruled out by the data.  A 30% disagreement over a region where the cross section is changing by more than a factor of ten is a small difference.

Fig 3 caption: Please give a reference for the RNA calculation in the caption and also state that the RNA calculation is normalized to the highest energy data point.  Describe the data points and lines in the caption, not the text (see line 274)

Fig 3: I'm not sure that it's fair to normalize the RNA calculation to the highest data point.  If you move the calculation down slightly, it looks reasonably consistent with all the data in its range.

l275: This paragraph is a bit clumsy.  Also, I do not understand why we discuss the difference between pn, pp and pd rescattering when there is no calculation yet and when the forthcoming calculation only will cover pd rescattering.  I suggest: "A third possibility is that the reaction dynamics could be dominated by hard rescattering.  Calculation of the cross section in the framework of the Hard Rescattering Model (HRM) [4] using elastic pd scattering data is in preparation [42]."

l286: replace with "We observe the onset of scaling at theta_cm = 90o at a momentum transfer to the deuteron t > 0.64 GeV^2 and a transverse momentum p_perp > 0.95 GeV/c."

l289: The sentence beginning "It is quite novel" contains two thoughts.  First, this is the first observation of scaling for heavier nuclei.  Second, the momentum at which it begins is very low.  I suggest rewriting the sentence as 'These momentum thresholds for scaling are remarkably low.'

l312: add 'E_gamma =' before '0.7'

l316: add 'a' before 'few'

l316, 317: delete both commas following 'data'

l328: add 'a' before 'few'

That is definitely enough.