The Standard Model of High Energy Physics based on the gauge group SU(3)c×SU(2)L×U(1) is a truly remarkable theory. It is highly successful in that ever more sensitive measurements have not revealed any significant deviation from its predictions. Furthermore, it is renormalizable and in that sense mathematically self-consistent. Nevertheless, we have strong reasons to believe it to be incomplete since it exhibits very peculiar patterns for which it offers no explanation. The basic constituents of matter are arranged into three seemingly identical generations or families of quarks and leptons, differing merely in their masses. We do not understand the pattern in the fermion masses, why there are families or why there are three of them. On the other hand, it is hard to believe that these features are accidental, that Nature has encoded no profound message in them. Furthermore we know that at least within the Standard Model there is an intimate connection between the replication of families and the gateway for CP violation; in addition, the latter phenomenon is a crucial ingredient in explaining why our universe is made up almost exclusively of matter rather than being more or less matter-antimatter symmetric.
We firmly believe little progress will follow from theorizing with existing data only. Coming to a better understanding of these mysteries thus represents a challenge to both experiment and theory; we have to be aware that nature – as has always happened in the past – might have another surprise or two up her sleeve.
How and to what extent can Heavy Flavour Physics impact on these questions? Does it offer novel windows onto New Physics beyond the Standard Model in general and onto new symmetries, such as Supersymmetry in particular?
These questions constitute the central theme of this Varenna course and the spirit that led us to organize it. The resulting scenario, as illuminated by the speakers, is very promising. Heavy Flavour Physics has accomplished enormous progress during the last few years: the last heavy quark, top, has been discovered and the quality of the collected data on the other relatively lighter quarks has dramatically improved. On the theory side, noticeable progress has been reported on new calculations of decay rates based on various techniques, such as QCD sum rules, heavy-quark mass expansion and lattice QCD. The theory of heavy-quark production is constantly improving and awaiting new results mainly on top, where its predictive power should be superior.
Major progress in addressing the questions outlined above is expected from the next generation experiments on CP violation and rare decays. The way in which CP is (hopefully) violated in the B sector could reveal mechanisms outside the Standard Model. Certain rare B decays, once found, could signal the intervention of New Physics and could even provide hints specifically for SUSY. In the charm sector, the non-conservation of CP would be a real challenge for the Standard Model: even a tiny violation in some particular decays would require new physics.
The list of important insights expected from Heavy Flavour Physics in the foreseeable future is actually much longer: here, we would only point out the fact that the research in this field is extremely active and in continuous evolution.
We believe that the lectures collected in this book present a comprehensive review of the current knowledge of heavy-quark physics, from the points of view of both theory and experiment. We hope that the material treated in this book may serve as reference for the segment of the high-energy community actively engaged in heavy-quark physics.
We would like to recall that during the school a lecture was devoted to celebrating the 50th anniversary of the discovery of the pion and its authors, Lattes, Occhialini and Powell.
We thank all the lecturers for their precious collaboration and the invaluable work in preparing the lectures.
We are grateful to the Italian Society of Physics (SIF) for having given us the opportunity to organize and carry on the school in the wonderful and historical Villa Monastero, surrounded by one of the most beautiful and inspiring landscapes of Italy.
Our special thanks are for the SIF personnel, Mrs. Enrica Mazzi, Franca, Ramona and Silvia, who gave us continuous support with efficiency and charme and made everybody's stay in Varenna very pleasant. We would also like to express our gratitude to Dr. Paola Rucci, Mrs. Carmen Vasini and all the editorial staff of the SIF for their friendliness and invaluable patience in preparing these Proceedings.