thank you for sending me your considerations concerning the present status of heavy ion reaction physics around the Fermi energy.
I think your remarks concern all the physics between the formation of compound nuclei and the meson threshold.
You have certainly not exaggerated the situation. I think we should honestly say that the situation is dramatic. The field is on the best
way to disappear: Last week I learnt that the only regular conference which was left, CRIS, will be devoted to cosmic rays next time.
I cannot count anymore the people who have left the field in the last years here in Europe and in the US.
This is certainly the time to ask ourself where this does come from. If you ask outsiders, they tell you that it seems that this physics
is little more than billard ball games with a mean field, like sucessfully implemented in BUU, QMD or LV and no pertinent result has
This may be true although in view of the fact that the ususally large error bars accomodate easily discrepancies but it is not the full
truth and here comes our own responsability. We are almost all doing this physics in a way nuclear physics was done 25 years ago:
small independent groups propose quite independent experiments in where quite different variables are measured. Even we have the
tendency to ignore the work done elsewhere. Theory makes for the experiments phenomenological models which describe the one
or the other observable.
But nuclear physics has changed.
High energy (nuclear) physics teaches us that progress is made by systematics: Two or three systems, systematically measured
over a wide energy range, with detectors which allow for the measurement of many observables, that makes this physics more
successful. With this approach theories have been discarded, systematic error have been reduced and finally theory was forced and
able to improve so a comprehensive understanding became possible.
At the Fermi energy this if of course much more difficult because the accelerators are different, many detectors are in use ... Now we
are confronted with the fact that we know many details but a comprehensive understanding of the physics is not at hand and therefore
funding becomes a big problem.
Since 15 years we fight (including myself) an almost religious war about the origin of multifragmentation (statistical or dynamical)
without having been able to figure out which experiments should be performed in order to solve the question. Experimental papers (Li
and Yennello, Phys. Rev. C52, R1746 (1995)) claim that equilibrium is not established whereas others - see f.e. the thesis of the
INDRA collaboration - claim exactly the opposite and never a common effort has emerged to figure out where these opposite views
come from and what we can learn.
Since 15 years we debate whether the theoretical models are good enough to determine the equation of state from the flow variables
without reaching any consensus because we never tested the models against each other like it is done since years at higher energies.
Therefore I think we have to change, we have to discuss whether the field is sufficiently interesting to be persued (what I believe), what
key experiments have to be done in order to understand the physics, how we can - despite all difficulties - arrive at a systematic
approach of the key questions and we have to start to compare the theories before we claim to have found something. The workshop at
the ECT would be a good opportunity to do this, may be even some homwork assignement can be done before for the theoreticians
which allows to discuss similarities and differeces of seemingly very similar approaches.
One thing, however, we should not do. We should under no circumstances write a review before we have sorted out all our problems and
differences. To give the other communities the impression that we are not able to do our homework is certainly the best way to kill the
Nevertheless the field has produced very nice theories of statisticl mechanics in finite systems which remein beautilful even if nature
has decided not to realize a statistical equilibrium at this energy.