The CLVIII Course “Hadron Physics” of the Enrico Fermi School, held in Varenna from June 22 to July 2, 2004, was almost entirely dedicated to Hypernuclear Physics and Antiproton Physics.
The first part of the Course focused on the last achievements and future perspectives of Hypernuclear Physics, born more than 50 years ago. Like other fields of Physics, experimental research on Hypernuclei started as a modest effort of a few small teams, focusing their interest on well-defined aspects. The results, interpreted by outstanding theoreticians, stimulated the construction of more and more sophisticated detectors that may be considered as Hypernuclei Factories, concerning both the production of Hypernuclei and the detection of all particles emitted in the different processes of decay. The main achievement of these Factories was to clearly demonstrate the special potentialities of Hypernuclear Physics in order to get unique information on nuclear structure, Hyperon-Nucleon interactions and four-baryon weak decays. This goal is made possible by the role of the Pauli principle, which acts in opposite ways in determining the spectroscopic and the decay features of Hypernuclei.
Concerning spectroscopy, besides having shown the validity of the shell model for many-body nuclear systems in a clear-cut experimental way, very recent experiments on high-resolution Gamma-spectroscopy of p-shell Hypernuclei performed at KEK and BNL allowed the precise determination of all terms in the Λ-Nucleon strong interaction.
The non-mesonic decay of Λ-Hypernuclei is the only window that can be open for a complete study of the ΛN → NN strangeness-changing four-baryon weak interaction, with experimental access to both parity-violating and parity-conserving terms. This topic, whose importance was known since long, received a renewed interest in the last few years thanks to excellent theoretical works and from first very clever complete experiments in coincidence performed at KEK.
These exciting physics potentialities stimulated several Groups to envisage new experimental ways to produce and study Hypernuclei, besides the traditional experiments with meson beams at proton machines (AGS and KEK). Electroproduction was proposed as a tool to obtain unprecedented energy resolution on the spectra of produced Hypernuclei thanks to the very high electron beam currents at TJNAF and to excellent performances of the associated magnetic spectrometers, and first results are just coming up.
Very innovative and unconventional is the study of the production and the decay of Λ-Hypernuclei at a Φ-Factory, which at first sight seems a nonsense since it foresees a fixed-target experiment at a Collider. However, a careful inspection of the merits of such an experimentation showed that counting rates and energy resolutions were quite better than those at proton machines. The FINUDA experiment at the Frascati DAΦNE Φ-Factory was designed and assembled just for this purpose, and the first, very interesting, results are of very good quality.
TJNAF and DAΦNE will produce a wealth of new data in this decade, but even more powerful facilities are approved and now are under construction. The J-PARC accelerator complex at Tokai (Japan) will supply meson beams with fluxes larger by two orders of magnitude than the existing ones. Hypernuclear Physics experiments performed with upgraded detectors could produce in some days the same amount of data produced in the last decade at proton machines. Furthermore, the study of ΛΛ-Hypernuclei, which are very hard to produce and study with modern electronic detectors (we recall that only four more candidates were very recently added to the two ones, already forty years old, observed with emulsions), could be addressed in a systematic way.
An alternative, again unconventional, way to produce and study the spectroscopy of ΛΛ-Hypernuclei is envisaged at the HESR antiproton storage ring at the recently approved antiproton complex FAIR in Darmstadt. Incidentally, this topic ideally bridged also the scientific program of the second week of the School.
The lectures for the first part of the Course were given by speakers that are at the top of expertise in Hypernuclear Physics: Professors Alberico, Gal, Hungerford, Majling, Nagae, Outa, Petrascu, Pochodzalla, Weise and Zenoni.
The second part of the course deals with several aspects of hadron physics that can be done using antiprotons. Hadron Physics is the physics of strongly interacting systems. In the past thirty years quantum chromodynamics (QCD) has evolved as the theory of strong interactions that describes the interaction among quarks through the exchange of gluons. QCD is believed to be well understood at short-distance scales, but this is no longer the case as soon as the basic quark-gluon coupling is no longer weak. This region of strong QCD is governed by non-perturbative phenomena leading, e.g., to the formations of hadrons. The underlying processes like confinement and chiral symmetry breaking are, however, not very well understood. This presents a profound intellectual challenge for both experimentalists and theorists.
Experiments with antiprotons have proven to be a rich source of information in hadron physics. In 1983, with the low-energy antiproton ring (LEAR) at CERN, a unique facility for hadron physics with antiprotons came into operation. Until its closure at the end of 1996, LEAR provided pure and high-intensity antiproton beams in the momentum range between 60 and 1940MeV/c with good momentum resolution. LEAR experiments have proven to be extremely successful and provide a rich source of information for the light-quark sector. The first production of true antimatter —antihydrogen— happened as well at LEAR. Very low-energy antiproton physics found its continuation with the AD ring at CERN after LEAR, while hadron physics requiring higher-energy antiprotons will have to wait for the new FAIR facility at GSI in Darmstadt to come into operation.
The antiproton complex of FAIR was inspired by the success of LEAR experiments and experiments done at Fermilab. At FAIR, a new antiproton storage ring HESR will allow for high-statistics antiproton experiments with center-of-mass energies up to ~ 6 GeV with most precise energy resolution. Therefore the whole spectrum of QCD exotic states like glueballs and hybrids will be accessible while at the same time charmonium and open charm quark states can be studied. Beams of antiprotons also allow the implantation of charmed particles inside nuclear matter and the subsequent study of their properties and interactions. The highly sophisticated PANDA experiment to perform all this physics is in its planning stages and should be ready for data taking in less than ten years from now. However, since there is a continuous interplay between physics goals and the design of an experiment, a course like the present one is extremely valuable to provide both training of students and scientists and discussion of new ideas. The lectures for the second part of the course were given in an enthusiastic and inspiring way by Professors Bettoni, Brodsky, Filippi, Hayano, Johansson, Koch, Kühn, Paul, Peters.
In conclusion, the organizers of the Course warmly thank the UNESCO and the EU for the very generous financial support to the School, which made a consistent participation of young physicists possible. Special thanks are due to Miss B. Alzani for the continuous and invaluable help during the Course, as well as to Miss R. Brigatti, Mr. G. Comini and Mr. L. Corengia of the Villa Monastero organization. Mrs. M. Missiroli and Mrs. C. Vasini are also acknowledged for their precious activity before and after the completion of the Course. Finally a special acknowledgement is due to Dr. A. Filippi, Scientific Secretary of the Course, for her continuous, patient and precious work at all stages of the organization of the scientific work as well as for many other practical duties.
T. Bressani and U. Wiedner