[Brahms-l] Fw: pt spectra from h-h, h-A and A-A at SPS (NA49 data) (fwd)

follow-up on previous e-mail
/fv
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Flemming Videbaek
Physics Department
Brookhaven National Laboratory

e-mail: videbaek@bnl.gov
phone: 631-344-4106
----- Original Message ----- 
From: <Boris.Kopeliovich@mpi-hd.mpg.de>
To: "Dmitri Kharzeev" <kharzeev@bnl.gov>
Cc: "Dmitri E Kharzeev" <kharzeev@quark.phy.bnl.gov>; "Yuri Kovchegov"
<yuri@qcd.phys.washington.edu>; "Mikkel B. Johnson" <mbjohnson@lanl.gov>;
"Hans-Juergen Pirner" <pir@tphys.uni-heidelberg.de>; "Kirill Tuchin"
<tuchin@quark.phy.bnl.gov>; "Alfred Mueller" <arb@phys.columbia.edu>; "Ivan
Schmidt" <ivan.schmidt@usm.cl>; "Larry McLerran"
<mclerran@quark.phy.bnl.gov>; "flemming videbaek"
<videbaek@rcf.rhic.bnl.gov>
Sent: Tuesday, March 15, 2005 6:26 PM
Subject: Re: pt spectra from h-h, h-A and A-A at SPS (NA49 data) (fwd)


> Hi Dima,
> thanks for the quick response. Let me comment on it.
>
> > The data you sent us extend to p_t less than 2 GeV, which is still below
> > the Cronin peak. The data thus do not tell anything about the
> > disappearance of the Cronin peak, and especially about the behavior
> > above p_t's at which the peak is normally located.
>
> I don't think that it is specifically important whether the Cronin maximum
> is above or below one. It might be even still above one, since the effect
> is much stronger at SPS than at RHIC. Important is that the effect of
> suppression at large xF is not only a property of soft, low pT, production
> (what has been known for decades), but spans across large a pT interval.
> You can see that the amount of suppression hardly depends on pT, as we
> expected. I think it is a challenge to find an explanation alternative to
> ours.
>
> > Moreover, there is a very important difference between the physics at
> > the NA49 energy of about 20 GeV (cms) and RHIC energy of 200 GeV, as it
> > is nicely illustrated for example in the article by Bourrely and Soffer,
> > hep-ph/0311110.
> >
> > As can be seen in Figs 2-5 of that paper, and in many calculations done
> > by Werner Vogelsang, NLO pQCD does a beautiful job in explaining the
> > pion p_t spectra at mid- and forward rapidities at RHIC energy. However,
> > these calculations fail miserably in describing the spectra at 20 GeV,
> > even at mid-rapidity. This shows very clearly that non-perturbative
> > phenomena dominate at 20 GeV, but the perturbative description of pp
> > interactions begins to apply at RHIC energy of 200 GeV.
>
> No mystery, this is exactly what our paper is about: not the perturbative
> QCD, but factorization breaks down when one approaches the kinematic
> limit. And you can see this in all the figures you mentioned from the
> Bourrely and Soffer paper. For instance, Fig.2 demonstrates that
> factorization works at xF=0 and medium-high pT, but then fails, and more
> at lower energies. Of course, one can move towards the kinematic limit
> increasing either xF, or pT. I don't know why you call this
> nonperturbative effects, according to our paper this is just due to
> problems with sharing energy withing high Fock components.
>
>
> >
> > It is thus unlikely, in my opinion, that the same mechanism is
> > responsible for the high p_t suppression observed at RHIC and SPS
> > energies. On the experimental side, it seems we still do not know
> > whether the high p_t suppression develops around the position of the
> > Cronin peak at the SPS energy.
>
> What should probably convince you is a numerical comparison of our
> calculations with the NA49 data. We will do it shortly using the same
> mechanism and the same computer code. Will see what comes out.
>
> All the best,
> Boris
>


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