[Brahms-l] white paper

A referee report has come back to us from Nuclear Physics.
Sould you have comments and suggestions in regards to this please send them to
Jens Jorgen and me. Since all experiments are still waiting for the STAR whitepaper this is
probably not urgent, but it would be good to have corrections and a response completed by 
the end of November.

regards
    Flemming and Jens Jorgen



Report on NUCPHA 4491:

I have a few general comments which require a modification of the text: (paper 
refers to the present paper) 
1. In the introduction, the conclusion on the SPS experimental program is an 
understatement and does not reflect at all what is concluded in the 2 references 
2,3 cited in the paper. The least that could be said is exactly what is written 
in the conclusion of the paper "In conclusion, we find that .... is strongly 
suggestive of a high density system that cannot be characterized ... but 
requires a partonic description" . Either the authors make their own conclusion 
on the SPS programs or they quote correctly the cited references. This will not 
minimize the outcome of RHIC. 
2. On the lattice results discussed in section 2, p4: lattice calculations with 
realistic quark masses (u,d,s) and zero baryochemical potential give now a much 
more precise value for the critical temperature than the range 150-180 MeV given 
in the paper. Moreover the exact order of the transition is not known and could 
as weel be a smooth cross over. This is in contradiction with what is stated in 
the paper: "Calculations indicate that .... The transition of second order". I 
suggest splitting the references in citation 10 and citing separately the 
lattice calculation with finite baryochemical potential at "Recently 
calculational technique ... "
3. There is constantly in the paper an incorrect interpretation of the 
experimentally observed suppression of high pt hadrons: the suppression does not 
test the degree of freedom of the traversed matter or the existence of 
deconfinment but only the color charge density. Therefore I think that the 
following statements are not correct:
o Section 6.1, p17: "... in a medium with a high density of free color charges" 
the color charges do not need to be free
o Section 6.3, p22-23: "the quantitative understanding... should be able to 
determine whether this interaction is at the partonic level of hadronic level".  
The interaction of partons with the medium occurs always at the partonic level, 
the partons in the matter being free or bound in hadrons. 
o Section 7, p27: ".. due to the interaction ... consisting of deconfined color 
charges" there is no way to tell that the color charges are deconfined. At best 
one can say that color charge density and the associated energy density are so 
large that only the partonic degree of freedom is conceivable.   
4. Section 3, p7:  on fig 2 you show "two possible distributions..." Even in a 
review paper it would be interesting to know where these two distributions come 
from. 
5. Section 4: On the estimation of the energy density: why not use the data to 
estimate the formation time from the average transverse mass rather than an 
"typical relevant energy scale". This will give a lower limit of the energy 
density, since transverse mass spectra reflect the system at freeze-out time and 
not at formation time, which I guess will be larger than the 5 GeV/fm3 derived 
in the paper. 
Section 5: I think that contrary what is written in the paper, thermal 
equilibrium is a requirement for defining the QGP if the definition of QGP is 
matter which is described at the partonic level at all momentum scales and over 
distances larger than the nucleon size. It is therefore not just "a tool in 
identifying the QGP". What is then important to know is what the energy density 
is at equilibration time (flow data can provide this value): is it still above 
the critical energy? This is I guess what is meant by "...the system has reached 
local equilibrium very quickly..." on p16.
6. Section 6.1, p20: it is concluded that "systematic studies ... will be 
required ... understand in detail the properties of the dense medium" I question 
the possibility to probe deep into the dense medium since the parton energy loss 
is proportional to the square of the traverse distance. Most likely hadron 
suppression will allow probing only a corona of the medium, the interior of the 
medium being opaque to jets.  This is hinted by the suppression of the far side 
hadron correlation.  
Wording I suggest making the following modifications for clarity and 
correctness. 
1. Introduction, 1st paragraph: I would refer to Shuryak (Phys. Rep.  61 71, 
1980) who suggested first the name quark gluon plasma in the sentence "Aptly, 
this ... (QGP). "
2. Section 3, 2nd paragraph: specify that AGS and SPS data correspond to central 
collisions
3. Section 5, 3rd paragraph: when you refer to figure 4 it is not "the yield 
seen in p+p" which is "multiplied by the number of participants" but the yield 
in Au+Au central collisions which is divided by the number of participants. 
4. Section 5.1, 1st paragraph: Figure 5 shows the rapidity density of pions, 
kaons AND PROTONS
5. Section 5.1, p14: specify that the value of 25 MeV is measured at mid-
rapidity. Could you put a more natural scale for mB on Fig 9 rather than 0, 19, 
43 ...
6. Section 6.1, 2nd paragraph: the scaling is done by the calculated average 
number of binary nucleon-nucleon collisions; it is not clear what the expected 
incoherent binary collisions means except for experts.  The next sentence is 
also esoteric: "In the absence of any ... from the embedding (!) ..." Try to 
reformulate something such as: in the absence of medium effects, at high pT, the 
nucleus-nucleus collision can be viewed as a superposition of elementary hard 
nucleon-nucleon collisions ... 
7. Section 6.1, p20, f1st paragraph, last line: specify "to rule out initial 
state effects" in Au+Au central collisions. The Cronin effect is also an initial 
state effect. 
8. Section 6.3, p 22, 1st paragraph: Could you make a reference to the 
discussion on the accuracy of the reference spectra at SPS energies.
9. Section 7, p24, 3rd paragraph: say that "saturation effects can be " best " 
studied" at RHIC "with ... at large rapidities"  Increasing vs allows to study 
low x phenomena even at central rapidity.
10. Section 8, 2nd paragraph: "This temperature compares .... QCD calculations" 
II guess you want to say that the chemical freeze out temperature compares with 
the critical temperature for the phase transition calculated by lattice QCD. 
11. Same section 3rd paragraph: I do not know what the "nearly ideal QGP" is. 
You could better say a QGP with the properties of a nearly ideal gas.
12. Same section p27: The sentence "At the same time intriguing suggestions ... 
has been found" should be rephrased. One cannot find a suggestion ! 
13. Same section p27: "a plethora" is to my feeling an exaggeration. 
14. Same section p28: I would not end with the last sentence: there is already a 
name, QGP, the goal is to understand the properties of the QGP.    
Typos: 
I have found a few typos: 
1. p4, 1st paragraph, line 11: ... transition can made à ... transition can be 
made
2. p4, 2nd paragraph, line 5: the quark condensate is note <q\bar{q}>
3. p5, 3rd paragraph, line 1: ... obvious that the the determining ...à ... 
obvious that the determining... 
4. p9, 2nd paragraph, line 8: ... nucleons(participant... à nucleons 
(participant...
5. p21, 3rd paragraph, line 4: ... $p_T > 2GeV$ à $p_T > 2$~GeV
6. p22, 2nd paragraph, line 11-12: was observed, (albeit a discussion ... at 
that energy. It ... à was observed (albeit a discussion ... at that energy). It 
...
7. p25, 4th paragraph, line 4: ... conditions for in energetic à conditions for 
????? in energetic
8. p26, 2nd paragraph, line 2: $5GeV/fm^3$ à 5~GeV/fm$^3$
9. p26, 2nd paragraph, line 6: ... $T = 175MeV$ à $T = 175$~MeV



With the suggested modifications, I recommend to the editor of Nuclear Physics A 
the publication of the paper in the special issue summarizing the RHIC 
experimental results. 

----------------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory

e-mail: videbaek@bnl.gov
phone: 631-344-4106



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