[Clascomment] OPT-IN: Shrunken particles pass freely through nuclear matter

[Luciano Pappalardo]

Dear authors, 

Thanks for this paper. The subject and the results are very interesting.
The text, however, still requires substantial improvements, especially 
in view of a publication on Nature.  

Below my detailed comments:

Abstract: The abstract is definitely too long and pedagogical. I propose 
          to retain only part of it (from line 13 to line 21): 
	  "We report the first evidence ... with the nuclear medium."
          The first part (from line 1 to line 12) should be incorporated 
          in the introduction (see next comment). The last part (lines
          22 to 24) should be moved to the conclusions 
          (see comment "pag.4, line 38"  below).


1st paragraph: The paper should begin with the first part of the current 
               abstract (lines 1 to 12) incorporating the first line of pag.2 
               and skipping lines 2 and 3 of pag.2:
             
               "Protons and rho (\rho_0) mesons are composite particles ... the 
               theory of strong interaction. The hadron wave function is a 
               superposition of states with different physical sizes. When hadrons 
               pass through the nucleus ... with dramatically reduced interaction. 
               These confugurations are of extremely small size (Small-Sized 
               Configurations or SSCs). Their interaction with the nucleus ...
               known as color transparency. Such SSCs of the hadron wave function 
               can be selected ... small electric dipole. The requirement of ..."


pag.2, line 9: "struck hadrons" -> "the struck hadrons"

pag.2, line 10: "struck quarks are close together" 
                -> "valence quarks are spatially close"

pag.2, line 16: ",i.e. the hadron transmission through a nucleus, with increasing 
                momentum"  

pag.2, line 23: "demonstrated" -> "observed"

pag.2, line 25: skip "(c is the speed of light)"

pag.2, line 28: "the quark abd anti-quark would each form a jet"
                -> "both the quark and the anti-quark would form a jet"

pag.2, line 32: "interaction of the hadron in nuclei"
                -> "interaction of the hadron with the nuclei"

pag.2, line 34:  add comma after "normal state"

pag.2, line 36: "on SSC formation, expansion and most importantly the interaction of 
                 the SSC as a function"
                 -> "on SSC formation and expansion and, most importantly, on its 
                 interaction as a function"

pag.2, line 38: remove semi-colon

pag.2, line 42-43: Rephrase: "So far, only limited experimental efforts have been 
                              devoted to the study of color transparency. Searches
                              for this phenomenon for the proton have all been 
                              ..."                


pag.3, line 7: "at still higher" -> "at higher"

pag.3, line 9: "provides the tool of choice to study color transparency."
               -> "is an ideal tool to study color transparency."


pag.3, line 13: remove "1/Q" 

pag.3, line 15: "decays to" -> "decays into"

pag.3, lines 20-25: This whole part (with the changes proposed in the next 2 comments) 
                    should be anticipated between lines 8 and 9 of pag.3. 

pag.3, line 20: "that the hadronic structure of high-energy photons allow for a photon 
                 to fluctuate"  
                 -> "that high-energy photons can fluctuate"

pag.3, lines 21-22: "distance l_c, known as the coherence lenght. It can be"
                    -> "distance l_c. This distance, known as coherence lenght, can be"

pag.3, line 26: "ration of the observed \rho^0's" 
                 -> "ration of the yields of \rho^0's"

pag.3, line 27: Anticipate here the definition of color transparency given at lines 17-19
                of pag.5. 

pag.3, lines 33-36: I don't think that the HERMES results have not enough statistical 
                    precision. The HERMES data show a clean trend of the transparency
                    as a function of l_c (fig. 1 of ref. 22). Furthermore, a 2-dim
                    analysis was also done (figs. 3 and 4 of ref. 22), which, in
                    contrast, is not reported in the present paper. Here, I guess, we
                    can only clame that the HERMES paper didn't report a 1-dim (i.e.
                    high statistics) plot of the transparency as a function of Q2
                    (though the 2-dim plots carry more information that the 1-dim one,
                    despite the corresponding reduced statistics).

 
pag.3, line 35: skip "were only suggestive because they" 

pag.3, line 38: "were key" -> "was the key" (subject is "combination")

pag.3, line 40: "compared to" -> "during" (cannot compare lenghts and times)

pag.3, line 41: "minimizing the \rho^0 meson decay" 
                 -> "minimizing the probability of \rho^0 meson decay"

pag.4, lines 1-2: "cannot mimic the signal of color transparency"
                  -> "is not indicative of color transparency

pag.4, line 3: "Fig. 3" -> "Figure 3" (better not using abreviations at the beginning
               of a sentence or paragraph).

pag.4, lines 7,12,14: either use "Q2 coefficient" or simply "slope". (parameter "a" 
                      represents the slope of the line. "Q2 slope" makes no sense.)

pag.4, line 21: "is a clear evidence"

pag.4, line 27: "evolves back" -> "evolves"

pag.4, line 30: "fm" -> "fm/c" (since you used "c" elsewhere)

pag.4, line 38: Insert here (after "exotic configuration") the last part of the abstract 
                (lines 22-24, pag. 1) (see my first comment above).

pag.4, line 44: "were chosen ... luminosities (10^34 nucleon cm^-2 sec^-1)."
                -> "were chosen such that the luminosities were comparable (10^34 cm^-2 
                sec^-1) for both targets."

pag.5, line 1: "data are taken" -> "data were taken"

pag.5, line 2: "inefficient detectors cancel" -> "detector inefficiencies cancel"

pag.5, line 4: "For the event selection"

pag.5, line 5: "is required" -> "was required"

pag.5, line 5: "and polar angle"

pag.5, line 7: "were used" -> "were applyed"

pag.5, lines 8-9: "reduce other reactions ... events."
                  -> "reduce contributions from other reactions with the same final 
                     state"

pag.5, line 10: "Fig. 4" -> "Figure 4" (better not using abreviations at the beginning
               of a sentence or paragraph).

pag.5, lines 12 and 13: "MeV" -> "MeV/c"  (since you used "c" elsewhere)

pag.5, lines 17-19: this whole part should be anticipated after line 27 pag. 3. 

Caption of Fig. 4: "the four-momentum transfer squared" 
                    -> "the squared four-momentum transfer"