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Dear Carlos,
Since you have invited the comment... I should say that I was
disappointed that the direct photon upper limit was not mentioned
at HIPS or afterwards. I agree that the point of view of the report
should be that there are now many observations which all point
encouragingly in the direction of QGP formation, although we are
not ready to claim observation of QGP. The direct photon upper limit
I believe is one of those important pieces of information as it most
clearly imposes an upper limit on the initial temperature, which in
turn indicates that the system has access to a large number of degrees
of freedom, not simply pion degrees of freedom. The J/Psi result
clearly indicates that a very dense, strongly interacting system has
been formed. And there are now many results which indicate that the
system formed is at, or close to chemical and thermal equilibrium,
and that the initial energy densities are large. I think that these
are important observations which have a broad consensus. I also
believe that it is true that the quality of the data and analyses
which are coming from the Pb data will significantly improve the details
of our understanding. This is a point worthwhile to make clear
by specific examples in such a report. However, I am rather concerned
that the report appears to rank the importance of the results, (with
an obvious one-to-one correlation to the remaining SPS experiments),
but at the same time does not attempt to make a very clear distinction
between established fact, and current topics of investigation and
possible dispute. Among the topics listed, I personally, am not
convinced that the threshold effect in the J/Psi suppression has been
demonstrated to be significant, nor that the low-mass excess is yet
on firm experimental ground. Confirmation of results by the same
experiment hardly ranks as a confirmation in my opinion. On the other
hand, the intermediate mass excess observed by HELIOS-3 and NA38
(NA50) is very difficult to dismiss, and surprisingly not mentioned
as a significant result. Similarly, while many observations are
consistent with thermalization I would certainly not claim that
it has yet been firmly established and that the freeze-out
temperatures are known to 10 MeV uncertainty. These happen to be
topics where I have reservations. My point is not to argue about
these topics, but simply to point out that more care should be
taken to separate established fact from interesting recent results.
I think that we would be doing a dis-service to the community to
imply too much as established fact, which might later have to
be retracted.
Sorry, I was sitting quietly, but your comment about the
photons was just too much provocation!
Regards,
Terry