Re: [Brahms-l] comments to pp paper

Dear Michael,
You say that pQCD reproduces mesons and pbar wel , but not p.  That may be one one the logical links we are searching for, for the physics discussion in this paper. That is to my recollection not stated in the paper. Rather we see a model reproducing p+pbar wonderfully, a pbar spectrum no one attempts to describe and yet negative statements about the AKK variant.
Now, I can follow your surmise that something is amiss with the proton, if indeed only the p's are not reproduced, however, why do things work at y=0 but not at y=3. Surely its tougher to move some fractional baryons all the way from y=5.6 to y=0 than just to y=3 (?).
cheers
and goodnight
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.
_________________________________________________________________________

  ----- Original Message ----- 
  From: Michael Murray 
  To: brahms-l_at_lists.bnl.gov 
  Sent: Friday, January 12, 2007 5:33 PM
  Subject: Re: [Brahms-l] comments to pp paper






       Dear JJ,
             I think that the most interesting part of the paper is that current models of QCD cannot reproduce the number of high pT protons at y=3 while they can do a good job for the mesons and pbars. This suggests to me that either we don't understand the distribution of low x partons inside the proton or that the models fail in how they move baryon number from the beam rapidity to y=3.


  Michael 



    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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