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Dear Colleagues,
I believe that in Chamonix we had a very useful discussion meeting of
the physics issues being addressed by the HI programme at the SPS.
From the personal contacts I had with many people, I would dare saying
that we all got a deeper understanding of the topics presently
generating the hottest physics interest. By the end of the meeting we
had a detailed list of points that we should attempt clarifying as
soon as possible, either by (re)analysing data already on tape, or by
taking new data, or by motivating people from different experiments to
work together so as to solve some (apparent?) discrepancies.
We are now in the process of preparing a summary report, to be given
to Lorenzo Foa by the end of November, that should contain a short
description of the present results and should indicate a list of
points that the community would like to see addressed, at the SPS, in
the next few years.
I would like to emphasise that we are NOT writing a "press release" on
the "convincing evidence for QGP formation in heavy ion collisions at
the CERN SPS". Although scientific progress can be made more
efficient by having discussion workshops as the one we held in
Chamonix, the real discoveries result from work in the counting rooms
of each experiment and not from "community votations", as (most of)
you know very well.
I truly hope that we can manage to produce a serious document and that
we can refrain from fighting about the relative importance of the
different topics/experiments. We had two days of intensive discussion
and if somebody feels there was not enough time to raise some issues,
we can have another meeting, next year, to continue the discussion.
The draft summary prepared by Berndt and Peter is, in my opinion, a
rather good starting point for the text we are aiming at. It is a
serious text, written in a positive mood without being too optimistic,
and I believe that it can induce a good reaction from the (present and
future) CERN management. I am confident that they will incorporate in
the next version many of the (good) ideas expressed in the messages we
received.
However, I am worried to see that responsible people spread around
opinions that give the impression we dont know what we have been doing
since 12 years. Consider, for instance, the following lines :
> In fact `low mass lepton pairs' are not related to QGP creation.
> Production of rare hadrons (J/psi, Omega) is obviously related but
> this relation is now not known to us (e.g. it is not at all clear
> whether one expects more or less aboundant production of J/psi and
> Omega for confined matter in comaprison to QGP).
> In my opinion the results which are the closest related to
> the creation of QGP are results on pion and strangeness
> multiplicities: their collision energy dependence and the
> absolute values at SPS.
I hope these lines will not reach the CERN management, otherwise they
could prompt closing the (present and future) heavy ion programme. If
we dont even agree on what we are looking for, there is no chance we
will ever establish having found it.
We have to carefully separate personal opinions and personal ignorance
that simply increase the already large entropy in the field, from a
critical evaluation of the status of SPS HI physics.
I truly hope that the final version of the report will not include any
statements of the kind :
> The main goal of the near-term programme is to search for the region
> in collision energy and size of the colliding nuclei in which
> transition to deconfined matter takes place.
It is clear to me, from the discussions during and after Chamonix,
that the "users" of the CERN heavy ion beam will not reach a consensus
on a global optimisation of the next few years of SPS running. Each
group has their own specific "main goal of the near-term programme".
We better accept it and stop pushing for an ideal global agreement
that, being impossible to reach, will only result in an increase of
stress and conflicts among the people involved.
Reality has shown that it is not up to the Chamonix participants to
make the next step: "and therefore the next few years at CERN should
be optimised by having the following program ...". That is the job of
the SPSC.
We must keep in mind that we are attempting a difficult exercise, that
has been unsuccessfully tried last year, among a much smaller group of
people. A second failure to produce a status report will certainly be
very bad for the whole field and can definitely compromise any hopes
of extending the programme beyond 2000.
As Ulrich Heinz wrote, where disagreement exists we should try to find
a formulation which most of us can agree with. This requires each of
us to express constructive remarks defending that our own results are
properly included in the text rather than negative messages aimed at
throwing everybody else off the table.
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Finally, my own comments on the present draft.
*** 1. End of the first paragraph:
"..., there is growing confidence in the HI community that this
evidence may be within reach"
I agree with Keijo and Emanuele that this sentence does not mean very
much, but the proposal of Emanuele
"All the experimental data can be explained by QGP formation, but are
not described fully by alternative hypotheses"
sounds too much as a press release and, in fact, I dont think such a
general statement can be defended. I would prefer :
"..., the HI community is confident that this evidence is within
reach"
*** 2. I dont think it is appropriate to have enumerated items. It
might give a feeling of relative importance among the items, and we
are not asked to provide that. Just replace \begin{enumerate} by
\begin{itemise}. The items (with "bullets") should appear in the
order in which they are mentioned in the previous paragraph (whatever
that order turns out to be in the final text).
*** 3. The first line of the last paragraph includes the words "for
the major experiments". You should delete them since you actually
mention *all* the remaining experiments, major or minor.
*** 4. The discussions on the "open charm" topic should be mentioned
in the text (outlook paragraph).
*** 5. After the sentence "NA45 is ready for data taking ..." it would
be appropriate to mention the upgrade being prepared by NA50 (and
encouraged by the SPSC last January) :
"NA50 plans an upgrade which should provide a similar capability for
measuring low mass dileptons in the mu+mu- channel, with completely
different background sources."
*** 6. I think it would be good to mention in the text the experiments
NA44, NA52 and WA98, since the other experiment codes are explicitly
quoted. I guess the "Hadron thermometry" and the "flow" paragraphs
should allow this small addition. I am surprised to see that nobody
complained (yet) about the absence of the topic photons. Besides, I
wonder if the topic "strangelet search" should also be mentioned
somewhere. I understand that there is no "notable achievement over
the past year" in terms of strangelet results. On the other hand, the
fact that no strangelets were found in NA52 is also a result, even if
a negative one, and has the advantage of being a rather well accepted
result.
Carlos