Theory  Hadronic Matter at High  The Future of High

How to proceed

Given the exciting developments described above, but also their rather recent character, the future directions are clear. The current SPS fixed target program is unique in the world, it addresses a well focused set of fundamental questions, it has entered an extremely productive phase and it has now to be brought to its full potential. With the exception of the low mass lepton pair measurements, statistics is in general not a problem. Rather the future program has to provide the answers to some well identified questions to settle the issues of equilibration, expansion dynamics and hydrodynamic behavior, anomalous J/ suppression, and in-medium modifications of the vector mesons. The continuation of the SPS program will include a low energy run around 40 GeV per nucleon which will increase the maximal baryon density but lower the energy density. This allows to play the two axes of the phase diagram against each other.

• It is of utmost importance that the SPS heavy ion program be brought to its full potential without any sacrifice so that the significant investment can be exploited. This program will require running for about five more years.
• The results becoming available may drive a request to continue the program beyond this period.

On the longer term, making use of the LHC for heavy ion collisions provides an unparalleled opportunity for exploring the physics of QCD matter in a qualitatively very different and unique region of extremely high energy density. The ALICE experiment is a common endeavor of the European high energy heavy ion community with smaller but growing participation from outside Europe. It is under preparation since 1990, has been approved in early 1997 by all relevant CERN committees and will be the future of the ultra-relativistic heavy ion program. Building a detector of the size and complexity required for LHC will be an unprecedented challenge for nuclear physics, and its successful completion will need the continued, strong and emphatic support and participation from the nuclear physics community in Europe.

• We strongly support, therefore, the construction of LHC at the earliest possible time.
• The realisation of ALICE at day one of LHC running is the highest future priority and will require the full commitment of the community and its resources.
• The time scale of LHC vis-a-vis RHIC allows for a limited European participation in RHIC. It clearly would be beneficial to participate in the science and further the development of new technologies. This would likely be reciprocated by the participation of US groups in ALICE.