Re: [Brahms-l] comments to pp paper

Dear Jens Jorgen

Thanks for your comments which I will digest later. I am presently at the DNP?APS town meeting at Rochster
and will go on vacation tomorrow (with e-mail)  It is very good that you got around to this, and we specificaly wanted
to get your input, so being later is better than never and may . It has indeed been difficult to describe well the issue of
'failure of pQCD for protons at large rapidities, since the figure shows a curve that apperently described the data,
but the pQCD does in fact calculate (p+p-bar)//2, and if protons comes from fragmentation it will predict (since the 
fragmentation is dominated by gg and qg) with roughly equal amount of p and p-bar. This is not fullfiled by the data
so this cast doubt on the proton description, while the other important point is the success of pions and Kaons.

Flemming

--------------------------------------------
Flemming Videbaek
Physics Department 
Bldg 510-D
Brookhaven National Laboratory
Upton, NY11973

phone: 631-344-4106
cell:       631-681-1596
fax:        631-344-1334
e-mail: videbaek @ bnl gov
  ----- Original Message ----- 
  From: Jens Jørgen Gaardhøje 
  To: brahms-l_at_lists.bnl.gov ; Flemming Videbaek ; debbe_at_rcf.rhic.bnl.gov 
  Cc: gardhoje_at_nbi.dk 
  Sent: Friday, January 12, 2007 7:34 AM
  Subject: comments to pp paper


  Dear Flemming and Ramiro,

  Here are a few comments on the pp paper.

  I apologize for being so late with this, but life is pretty busy these days. So I have succombed to the bad practice of complaining just before submission- something that I have complained about myself repeatedly! Mea culpa!.
  The comments below are being made in an airplane after several readings of the paper with remarks in the margin. The guy next to me is pretty bulky and its hard to type. 


  Hans Hjersing Daslgaard and Casper Nygaard (NBI) should be added to the list. They were part of taking the data and have been working actively on BRAHMS ever since.
  Abstract: 
  remove 'first time'.
  I would bind the last 2 sentenses together with '... suggesting tha t....'
  A main point of the paper seems to be that the p/pi ratios are different for the 2 charges. I would add a sentence to that effect. 


  p1 col1.: state FERMILAB and SppS energies for completeness.
  p1 col 2:  This letter reports the first measurements of unbiased diff. c.s. at high rapidities for ....
                 Produced mesons (?) ..... well described, but the yeild of protons and anti protons at high rapidty fails as QCD models do not include a complete description of the mechanism driving baryon transport ... .

  I would probably move the paragraph  'Collider measurements ..' up before the paragraph 'This letter.....'. I read as an introductory paragraph.

  Para: The data were taken...
  AT these rapidities the geom acc. and the pid of THE EXPERIMENT ...
  State the pt values to be compared with the kinematical limit.

  p2.

  FIg 1 has a lot of white space. I suggest cutting on the pt axis at 5 GeV/c and prob. on the ordinate one decade higher to increase useful fig. size.

  col2. an spectrometer ->a s....

  paragraph before the transverse polarisation.

  The satement 'careful study of the data..' appears weak to me. Elaborate or change to a simple statement 'It is ....'

  p3.
  reference to table 1. I don't think that a PRL should contain a fulll 2 column table just with systematic errors. Surely the syst errors can be listed in the text. That will also save you some space.

  I don't really understand the sentence : 'The data were placed ...iterative process'. 
  I may guess at what you mean (binning at high end of spectrum), but it appears from the text  that you change the data points around to make them agree with a fit! Not so hot for an experimentalist


  Fig. 2 migh win in clarity by adding a legend showing that circles are (+) and squares are (-) charge. 

  Sentence : *the yield of mesons drop rapidly ....in contrast to protons...'. Can this be seen from the figure?

  Sentence : The upper panels of fig 2 show...consistent with pion prod. dominated by valence q. fragm. 
  How do I see that? I would rephrase. That implies some specific input from theory.

  'The small value ...are a clear indication....' This is not clear to me. It is a main point of the paper and merits elaboration. 

  p3,  column 2. 

  where z is the fraction of ... and the functions fragmenting ... . I suppose a D is missing here before the functions.

  last para.
  delete more in ' ..more data made av....'


  Now here I come to my prob. more serious comments.

  I find the comparison of data to the two pQCD sets  (mKKP and AKK) confusing and the statements unclear.

  What I understand to be the case is that:
  1) mKKP can reproduce the meson data well, but cannot calculate the baryons (?) or does not reproduce the baryons (?). 
  2) AKK can do the total p+pbar and agrees with STAR data  at y=0. From the plot in the paper it obviously reproduces our total p+pbar data. So from that I would assume that AKK is a wonderful model.
  3) There is some unexplained issue related to the AKK physics that led you to distrust the meaning of the AKK set (?)

  There seems to be some logical link missing here. What is the point you are trying to make.? 

  I suppose that what you are tying to say is that AKK does not -at the same time as reproducing the total - reproduce the pbar/p ratios and therefore the agreement with the data must be 'accidental'. This is not demonstrated to the reader.

  The issue is therefore not clear. What is the exp. surprise? That there are many high pt protons? I somehow lack a demonstration that this is not expected from theory. The shown curves do not evidence that- on the contray : all fits well.
  Finally, the issue of the charge ratios (p/pi) being different is not taken up in the comparison to theory. So why is this surprising?. Earlier on you say that you expect soft p spectra. Is this clear from pQCD? AKK does, as you show, reproduce the total p+pbar spectrum.

  In summary I find that the main physics points of the paper are unclear.

  If you can outline the reasoning to me in an email I will try to express it as a paragraph for discussion --- I have to make amends for being so late with these comments.

  cheers
  JJ 



  _________________________________________________________________________
  Jens Jørgen Gaardhøje, Professor, Dr. Sc.
  Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark.
  Tlf: (+45) 35 32 53 09, secr. (+45) 35 32 52 09, Fax: (+45) 35 32 50 16.
  UNESCO Natl. Comm.: secr. (+45) 33 92 52 16.
  Email: gardhoje_at_nbi.dk.
  _________________________________________________________________________



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