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· Promote the exchange of information and views among the members of the international community of physicists in the field of Nuclear Physics.
· Recommend for IUPAP sponsorship, international conferences, symposia and seminars which qualify for support under Union regulations.
· Maintain liaison with other Commissions
The work of the Commission is carried out at meetings and by correspondence. The annual meetings are scheduled during conferences sponsored by the C.12 Commission. Amsterdam (94), Beijing (95), Williamsburg (96). Participation by members remains at high level.
1994 Nucleus-Nucleus Collisions, 5/30-6/4, Taormina, Italy
1994 Few-Body XIV, 5/25-5/31, Williamsburg, USA
1994 Nuclear Data for Science and Technology, 5/9-5/13, Gatlingburg, USA
1994 Symmetries in Subatomic Physics, 5/16-5/18, Taipei, Taiwan
1995 Weak and Electromagnetic Interactions in Nuclei, 6/12-6/16, Osaka, Japan
1995 International Nuclear Physics Conference, 8/21-8/26, Beijing, China
1995 Cyclotron and their Applications, 10/8-10/13, Cape Town, South Africa
1995 Exotic Nuclei and Atomic Masses, 6/19-6/23, Arles, France
1996 Particles and Nuclei XIV, 5/22-5/28, Williamsburg, USA
1996 Quark Matter, 5/20- 5/24, Heidelberg, Germany
1996 Electromagnetic Isotopes Separators and Techniques related to their applications, 9/23-9/27, Bad Dürkheim, Germany
1996 Radioactive Nuclear Beams, 6/3-6/7, Omiya Saitama, Japan
The proposal to hold the next International Conference (1998) in Paris has been approved by the C12 Commission.
Nuclear physics is a frontier field, with strong links to other branches of physics. Nuclear physics investigates all forms of matter bound together by the strong, short-range forces arising from the interactions between quarks and gluons. Nuclear physicists study the structure of the nucleon, the properties of atomic nuclei, the formation of the elements via stellar burning, the characteristics of hot dense nuclear matter as it occurred in the early universe and in the collisions of ultra high. energy heavy ions.
Hadrons and nuclei provide testing grounds for new theories. New experiments testing fundamental symmetries (violation of parity, charge symmetry, time-reversal invariance, etc.) provide opportunities for the search for physics beyond the Standard Model of quarks, leptons and unified forces.
Nuclear physics has a central contribution to the understanding of many astrophysical problems, from cosmology to stellar structure. One of the focus of this field is the solar neutrino problem. Do neutrinos have mass? Recent results indicate a limit to the neutrino mass below a few eV from Tritium b-decay experiments. There are some hints that they oscillate. A new generation of neutrino detectors with the goal of solving the solar neutrino problem has already put major constraints on possible neutrino masses.
The diversity of laboratories around the world has a major impact on technology and society: energy production, medical imaging (NMR, PET...), cancer treatment, food processing, safety in industry, preservation of artworks, archeology, anthropology and geophysics. New high intensity protons accelerators are being studied for the burning of nuclear wastes.
The detailed observation of the evolution of shell effects with nuclear sizes, superdeformations, the discovery of new magic numbers and superheavy elements have a major impact on the understanding of the properties of level densities of finite quantum systems. The ability to create nuclei at the limits of stability generates intense world-wide interest to build new facilities.
· A few years ago, observing superdeformations in nuclei was at the limit of experiments. The new generation of multi-detector gamma-ray arrays, GAMMASPHERE, in the United States and the first stages of EUROBALL, in Europe, have enabled a detailed spectroscopy of these superdeformed bands. In particular transitions from superdeformed to normal shapes have been observed by both collaborations at the end of 1995. Large collaborations have already gathered around these spectrometers and are continuing to grow. These new spectrometers are expected to be completed in early 1997. They will be able to detect g-ray cascades which are produced with a probability of 10-5 or less and give conclusive evidence on the existence of nuclear hyperdeformations where the axis ratio approaches 3:1.
· Long lived, light nuclei with a neutron halo, 11Li, 11Be, 19C,... have been observed. In these nuclei the neutron orbits at a large distance from the center of the nucleus, typically of the order of 10 fm.
· Nuclei at the limit of stability, 78Ni and 100Sn have been identified, supporting the assumption of the doubly magic nature of these nuclei.
Superheavy elements, Z=110,111,112 have been synthesized in heavy ion collisions observed at GSI in Darmstadt. The heaviest element Z=112, A=277 has been discovered February 9, 1996, in the collision of a Zn ion beam on a Pb target. This element has a relatively long life 280 ms and decays by a emission. One is now very close to the region Z=114 predicted by theory to correspond to a new closed shell.
Quantum chromodynamics (QCD) describes the interaction of quarks and gluons, the underlying constituents of strongly interacting matter. However the way in which quarks and gluons are confined into the nuclear constituents, protons and neutrons (nucleons), and into the mesons generating nuclear forces is not well understood. Experiments have attacked this problem to provide a bridge between QCD and our phenomenological description of nuclei and nuclear forces.
Can one ascribe the nucleon spin to the three constituent quarks? Recent polarized lepton-nucleon scattering experiments from CERN and SLAC suggest no. The origin of the missing fraction of the nucleon spin remains a mystery. However these recent data clearly confirm the validity of the Bjorken Sum Rule. This provides a beautiful confirmation that QCD accurately describes all aspects of the strong interaction from very low energy processes (such as b decay) to the highest collider energies. New experiments will measure the proton, the deuteron and 3He spin structure with a 50~GeV electron beam at SLAC. A new experimental approach proposed by the HERMES collaboration at DESY uses a novel technique based on an atomic gas jet target of polarized nucleons, injected into a beam of polarized electrons circulating in the HERA electron--proton collider. Several experiments have been proposed to measure the amount of gluon polarization, such as the study of polarized proton--proton scattering at the new Relativistic Heavy Ion Collider (RHIC) being constructed at Brookhaven in the US. Measurements of the Drell-Hearn-Gerasimov sum-rule, of neutrino scattering at low energy and of the strange quark form factors will also bring important information on the strange quark content of the nucleon.
A few years ago, a major limitation for nuclear studies with electromagnetic probes was the duty factor of the accelerator. Most data were obtained without the coincident detection of particles produced in the final state. This situation has recently changed. Several electron accelerators (Amsterdam, Bonn, Mainz, NIKHEF in Europe, MIT-Bates and CEBAF in the United States) have now continuous electron beams. A wealth of new coincidence experiments is now in progress. Among the first results, the measurement of proton momentum distributions has extended our knowledge on nucleon nucleon correlations beyond 700 MeV/c. Another focus of activity is the electroproduction of pions at threshold, to study the low energy limit of QCD (chiral symmetry).
Progress in polarized electron sources and polarized targets has been considerable in the last few years, giving access to new information on the structure of nucleons and nuclei. The recent measurement of the electric neutron form factor with high accuracy is one of the striking illustrations of the development of this new field.
Some recent experiments have found hadrons which behave like "glueballs", that is, hadrons made of gluons not quarks.
Most studies of nuclear matter to date have explored and clarified its properties at or near normal temperatures and densities. Heavy ion collisions at intermediate energy and at very high energy study the analog of a liquid-gas phase transition and the transition from hot dense matter to a quark-gluon plasma. This latter phase of matter in which quarks and gluons are deconfined existed for a short time after the Big Bang and may exist today in the cores of neutron stars.
A large activity is devoted to the study of the nuclear response to induced collective motions of increasing amplitude. Multi-phonon excitations have been discovered at GANIL and SIS. These collective excitations of the nucleus correspond to giant resonances built on top of other giant resonant states.
The study of the properties of the nucleus under a variety of conditions of pressure and temperature is extensively carried out at GANIL, MSU and SIS with a new generation of 4p detectors. Experimental evidence on the appearance of multifragmentation is now well established. For the first time a complete vaporization of highly excited nuclei into neutrons, protons and a particles has been observed.
The existence of a Quark-Gluon-Plasma, a deconfined phase of quarks and gluons, is a definite prediction of QCD. Lattice calculations predicts a deconfinement phase transition in systems with vanishing baryon density at temperature of order Tc=150 MeV leading to the Quark Gluon Plasma. The production of the vector mesons J/Y and Y', made of a pair, is modified by the nuclear environment. Chiral symmetry appears to be restored during the same phase transition.
The early exploratory program with light ions up to 32S at Brookhaven and CERN have shown that high energy densities can indeed be obtained and produced evidence of the onset of new, collective phenomena. Some characteristic features of these reactions are surprisingly close to the ones expected for a macroscopic lump of hadronic matter heated to a temperature of about 150 MeV. The recent experiments with heavy ions Au and Pb, both at Brookhaven and CERN should determine to what extent one can actually establish a regime of thermodynamic behavior. They should reach baryon densities larger than the ones in the core of neutron stars.
The strangeness enhancement predicted by theory is found in several different channels. The change in the spectrum of the J/Y and the suppression of the Y' have been extensively studied in order to separate the effects known from the ones observed in nucleon-nucleus collisions from those due to color screening in a Quark Gluon Plasma. The large suppression of the Y observed recently at CERN is a possible indication that the onset of quark deconfinement has already been observed.
New radioactive beam facilities are being built around the world using the ISOL technique to produce radioactive beams with energies of 2 to 20 MeV/nucleon for nuclear structure studies at the Coulomb barrier. HRIBF at Oak Ridge (1996), REX-ISOLDE at CERN (1998) SPIRAL at GANIL (1998), ISAC at TRIUMF (1999).
The major new facility being built in Europe is the Large Hadron Collider LHC at CERN expected to collide protons at about 6 TeV/nucleon in 2005. From the start the LHC would also accelerate ions, during a few weeks per year., with luminosities 1027 cm-2 s-1 for Pb-Pb. ALICE a dedicated detector for heavy ion collisions is being designed along with two major p-p detectors.
NuPECC has recommended to study the possibility of building the ELFE project at DESY. ELFE is a 15-30 GeV continuous electron beam of high energy resolution and high luminosity on fixed nuclear targets. The current project being studied is to use HERAas a stretcher ring combined with a segment of the superconducting linear collider TESLA.
Two new facilities correspond to major construction budgets in the United States.
· CEBAF is a superconducting electron accelerator combining for the first time a continuous beam of high intensity and high energy resolution up to 6 GeV. One will have access to a new research domain on nucleon and nuclear structure. Three distinct experimental end stations are designed to be simultaneously used. The construction of CEBAF is essentially finished, experiments have started. The continuous acceleration of electrons at CEBAF is made possible due to a technological breakthrough in superconducting cavities.
· RHIC is a relativistic heavy ion collider in construction at Brookhaven. RHIC will collide 100 GeV/nucleon beams from hydrogen to gold, starting shortly before the end of the century. Luminosities should exceed 1026 cm-2 s-1 for Au-Au. Two large detectors, STAR and PHENIX are under construction, as well as several smaller experiments.
Two major new projects emerged in 1995 in Japan. Both projects are expected to start in 1998. International collaboration is very much welcomed for these two projects.
· Japan Hadron Project by INS (Institute of Nuclear Studies of Tokyo) and KEK. The project consists of a 200 MeV linac followed by a 3 GeV booster (25 Hz, 200 mA) and a 50 GeV main ring (5-10 mA). This project is the successor of the KAON project, proposed in Canada.
· RIKEN Radioactive Beam Factory. A superconducting cyclotron (K=2400 MeV) and double storage rings. This machine would combine both a high beam energy and a high beam intensity.
Japan is also completing a beauty factory at KEK in 1998 and has positioned itself very strongly for progress in Nuclear Physics.
Two vigorous new nuclear theory centers have been recently created at Seattle in the United States and at Trento (Italy) in Europe. These centers have each year an extensive program of workshops with a large international participation from all over the world. Specific programs are devoted to interdisciplinary topics.
International cooperation in nuclear physics has become and will continue to be extremely lively and productive at the scientist-to-scientist level. With the increased scale of major facilities, a number of more formal cooperative agreements have been pursued to open up scientific opportunities for the international community at unique facilities. In turn, these facilities have been able to extend their scientific reach through instrumentation development by the international partners. Current examples include, among many others, the important detector contributions by European and Japanese scientists to CEBAF and RHIC in the US, and US participation to the Sudbury Neutrino Observatory (SNO) in Canada, US collaboration in CERN programs with muons (SMC), antiprotons and heavy ions, US and Canada participation in the HERMES program at the DESY/HERA facility in Germany. In Europe, several countries have joined their efforts to build a powerful 4p gamma ray spectrometer, EUROBALL and TAPS, a two arm photon spectrometer.
In Europe, Japan has recently become an observer at CERN and will participate in the LHC. In the United States Japan will participate to the heavy ion program at RHIC with the PHENIX collaboration and the RHIC Spin collaboration.
The Nuclear Physics European Coordination Committee (NuPECC) of the European Science Foundation now coordinate nuclear physics activities in Europe. The Committee consists of 21 members from 14 European member states including Austria, Belgium, Denmark, Finland, France, Germany, Italy, The Netherlands, Norway, Portugal, Spain. Sweden, Switzerland and United Kingdom.
A new journal edited by NuPECC, "Nuclear Physics News International" regularly provides information on the status, new directions and opportunities of nuclear science all over the world.
A subcommittee of C12 called ICHIA (International Committee on High Intensity Accelerators), chaired by H. Feshbach, organized a meeting, held in Amsterdam in December, 1994, which brought together leading nuclear physicists with leading government officials responsible for nuclear physics programs around the globe. This meeting pointed to the steps needed now for the nuclear physics community to respond to the development of Nuclear Physics worldwide. As a result. at the 1995 INPC conference in Beijing, C12 accepted the recommendations that ICHIA be dissolved and replaced by a new C12 subcommittee (International Cooperation in Nuclear Physics) with a more specific mandate for the new steps.
The creation of ICNP corresponds to a build-up process that has taken into account the discussions with the nuclear physics community at the occasion of several meetings. The goals of ICNP are to:
· Provide a report on the status of nuclear physics and on new scientific directions.
· Identify new opportunities for international collaboration in pure and applied nuclear physics.
· Establish a forum for the discussion of the provision of future facilities and instrumentation.
· Facilitate access to and utilization of existing and future national facilities.
· Promote international collaborations between scientists.
ICNP will involve active members of the scientific community, the research organizations and links to the funding agencies. ICNP will regularly report its work to the nuclear physics community at the occasion of one of the major conferences sponsored by IUPAP.
Four distinct sectors of the world have been identified and it is suggested that each one be represented by three scientists: Europe (NuPECC Chairman + two other scientists), Japan and Asian Pacific (Japan NPC Chairman + two other scientists), United States and Canada (NSAC Chairman + two other scientists), other areas (C12 Chairman + two other scientists).
Finally we would like to express our deep appreciation of the work achieved by H. Feshbach, chairman of ICHIA to promote international collaboration. We are most grateful to Y. Yamaguchi, chairman of IUPAP for his continuous interest and his important contribution to the work of the C12 commission.
B. Frois and E. Vogt