From: Michael Murray (mjmurray@ku.edu)
Date: Tue Aug 26 2003 - 14:16:04 EDT
Dear Flemming and Jens-Jorgen,
here are some comments on the beam use proposal.
(Flemming could you please forward this to brahms-l if my attempt fails. JJ
stop burping.)
The most important thing to do at the moment is a binary search on the
limits of high Pt suppression. This should be consistent reflected in both
our beam request itself and the language of the proposal. Both Fe+Fe and
63GeV running represent changes of about a factor of 4 in one of the
relevant variables. Conceptually what we would like to do is to pass beams
of 3-4GeV quarks and gluons through slabs of this "New State of Matter" that
have varying thicknesses and energy densities. To change the energy density
one must clearly lower the energy. To change the thickness of the slab one
must change the centrality or the beam species.
The discussion of the slab thickness brings to mind the huge fight NA50
precipitated with their discussion of J/psi suppression versus "L". Here L
represent the average path length of a J/psi in the medium. If you remember
they showed the ratio of J/psi over Drell Yan production with several
thresholds who width was about 0.5fm. Many people rightly pointed out that
it was impossible to have such resolution in L. Also their own data showed
that the only place where L was reasonable well defined was for entral
collisions. One thing that I learned from my HELIOS calorimetry days is that
a nucleos is not a uniform blob of matter but a liquid with strong
nucleon-nucleon correlations. (Kris knew this 10 years before I did.) A
given peripheral Et or multiplicity bin contains a very wide range of impact
parameters.
Thus I think that a proper study of size effects has to be done by comparing
central collisions of different species. The physics case for lower energy
running is equally strong for high Pt and perhaps stronger for the soft
survey physics. However we must focus on High Pt suppression and the rate
estimates strongly favor light ion running.
As for the RBUP itself we should ram home our intention to focus on high Pt.
For section 2.4 the "High Pt suppression" and "System size" subsections
should go before "Bulk Properties".
On page 8 we should say that
"High Pt suppression is CURRENTLY the chief QGP signal" (Not "developing
as")
On page 9 after "In summary .." why do we ask for more time to study high Pt
at y-0? How can we compete? Why not sit at 25 degrees and do y=1.5?
On page 12 for the 27 week table Run 5 the Si+Si (Fe+Fe) entry should be
above the pp running.
For the lower energy running I would put a positive spin on the rates by
saying that a later run will get the most benefit out of the increased
luminosity.
After the Hi Pt suppression I think that the longitudinal dynamics is the
most important thing we can tackle. Our dN/dy distributions are beatiful and
unexpected. Some kind of size measurement versus rapidity is the next step.
Yours Sincerely,
Michael
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