Towards a Network of Complementary  No Title  Introduction

Recommendations

General Recommendations

Nuclear Physics focuses on the study of the structure and dynamics of complex systems of particles which build up hadrons and nuclei. Nuclear Physics has also a broad spectrum of applications and a strong impact on other fields of science, as presented in the 1994 NuPECC report on «Impact and Applications of Nuclear Science in Europe». Nuclear Science remains fundamental for the development of future energy technologies. A number of complementary research facilities in the field of Nuclear Physics are established in Europe and are operated mainly by national institutions, funded by national agencies and used by an international community of scientists. The exploitation of this network of facilities is co-ordinated by international advisory boards. This co-ordinated approach has led to a remarkable scientific productivity and coherence in the field. It is therefore very important to maintain the open access to this network. Future facilities and detectors will considerably exceed today's systems in size, complexity and cost and will mostly have to be realised in the framework of international collaborations. NuPECC therefore recommends that national funding agencies should become involved already during the planning stage of these new facilities. NuPECC is ready to help in this process. For certain projects such as second generation radioactive ion beam facilities and a future high-energy electron accelerator the necessary steps should be taken soon.

    Progress in Nuclear Physics depends not only on a strong experimental programme but also on the excellence of research in Nuclear Theory. NuPECC therefore recommends that universities and research institutes assure the future of this part of the field by appointing young scientists in Nuclear Theory. The European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) in Trento provides a forum for the discussion of new ideas between theorists and experimentalists. NuPECC recommends that long term financial support for ECT* from European sources be assured.

NuPECC emphasises that universities throughout Europe play a key role for the future of Nuclear Physics, both by providing the basic nuclear physics education and the interface to other disciplines and by being the home base for groups doing experiments at large facilities. NuPECC recommends that the strength of the university home base be maintained. 

Nuclear Structure under Extreme Conditions

The understanding of Nuclear Structure has made significant progress in the last decade and, at the same time, has generated a number of challenging new questions. They address the properties of the nucleus at the limits of excitation energy, spin, isospin and mass. The rapid development of experimental techniques leading to highly efficient detector arrays for gamma-rays, charged- and neutral particles makes the investigation of central issues of Nuclear Structure possible. These include extreme nuclear shapes and their evolution as well as the influence of the thermal environment on collective modes at low and high excitation energy. The next generation of radioactive ion beam facilities will open the way to the study of new Nuclear Structure phenomena near the drip lines, such as halo nuclei, neutron skins, neutron-proton pairing and exotic collective phenomena. At the same time, they will provide more insight into the process of nucleosynthesis. Extrapolating from the recent observation of element Z=112, the synthesis of superheavy elements near the expected island of stability will become within reach with the new generation of high luminosity facilities.

    Nuclear Structure studies rely on a continuing availability of accelerators providing high quality beams of stable ions and electrons. In order to fully exploit the important recent investments in facilities and instruments, those accelerator laboratories which form a European network of complementary facilities must therefore be supported and further improved.

    Nuclear Structure studies at the limits of stability require the highest possible luminosities and detection efficiencies. The European collaborations involved in the development of powerful new detector systems and the operation or the construction of the radioactive beam facilities and the R&D on high power target-ion source combinations should be strongly supported in order to reach this goal.

    NuPECC recommendation: A study group should be set up in order to investigate the main options for second generation radioactive ion beam facilities in Europe. 

Nucleus-Nucleus Collisions and the Phase Transitions of Nuclear Matter

Collisions of atomic nuclei at intermediate and high energies address some of the key questions of modern Nuclear Physics. They are the means to study the phases of nuclear and hadronic matter as a function of temperature and density of the system. Several phase transitions are under investigation. At low density and temperature, the nucleus may ``multifragment'' and evaporate into a cold gas of nucleons and light nuclei. At high density and temperature, hadronic matter may dissolve into the quark-gluon plasma via the associated phase transitions of deconfinement and of chiral symmetry restoration. At energies and densities below this regime, the equation of state of hot and dense hadronic matter may be mapped out. The quark-gluon plasma phase transition and the equation of state of dense matter are of astrophysical and cosmological relevance, e.g. for the recreation of the conditions as they existed about a microsecond after the Big-Bang, the structure of neutron stars and the evolution of supernovae.
 
    All these experimental activities must be accompanied by theoretical investigations using teraflop computer systems. Recent advances in parallel computer systems offer the opportunity to carry out the necessary tasks.

    In order to investigate the phase transitions of Nuclear Matter, the complementarity in energy and the variety of beams of existing facilities should be maintained and existing detectors further developed.

    NuPECC recommendations: A study group should be set up in order to investigate the possibility of a European effort towards large scale computing. The realisation of a dedicated heavy ion detector in time for the start of the LHC is endorsed as the highest priority of the high-energy heavy ion community. 

Quark and Hadron Dynamics

The study of the structure of baryons and mesons in terms of the quark and gluon degrees of freedom offers many new challenges that Nuclear Physics will have to address during the coming decade. Achieving a quantitative treatment of the confinement regime, which cannot be treated perturbatively, is at the basis of a more fundamental description of nuclei in terms of elementary constituents and interactions. At the same time the understanding of quark degrees of freedom is indispensable for the study of Nuclear Matter under extreme conditions such as they occur in the quark-gluon plasma and in astrophysical objects. Addressing the quark and gluon degrees of freedom requires the development of new theoretical concepts and the investigation of observables through exclusive measurements. The corresponding experiments require high-energy high duty cycle lepton beams of a luminosity much beyond the ones presently available.

    High precision measurements at low energy making the best use of existing facilities using electromagnetic and hadronic probes remain essential.

    For the time being, the study of the hadron and quark dynamics at higher energy should be pursued with priority at the existing facilities in Europe and in the US.

    NuPECC Recommendation: As a new initiative, a high luminosity and high duty cycle electron facility of at least $\mathbf{\sqrt{s}=7 GeV}$ ( $\mathbf{{\it E}>25 GeV}$ for fixed target experiments) should be built. 

Nuclear and Particle Astrophysics, Neutrino Physics, Fundamental Interactions

The impact of Nuclear Physics on other fields of science is particularly strong for Astrophysics, Neutrino Physics, and the study of Fundamental Interactions. The knowledge of nuclear properties, in particular of exotic nuclei, and of the nuclear equation of state plays a crucial role in the understanding of many astrophysical objects or events, especially explosive ones. High intensity low energy stable and radioactive ion beam accelerators are essential tools for the measurements of cross-sections relevant for astrophysical processes. Many of the highly sophisticated techniques used to unravel the neutrino properties are common with Nuclear Physics. The use of the Nucleus to study the fundamental interactions and their symmetries implies a deep knowledge of this complex system and the utilisation of nuclear techniques.

    Involvement of Nuclear Physicists in a number of experiments on neutrino mass, double-beta decay and dark matter should be supported, including the development of new techniques using cryogenic and superconducting detectors. High intensity pion, muon and cold neutron beams for the study of fundamental symmetries and rare decays should continue to be available.

    NuPECC Recommendation: An underground accelerator for background free measurements of important astrophysical cross-sections at thermal energies should be constructed.