11 July 2014
Professor Yoshihide Sakai
Co-spokesperson, the Belle Collaboration
The High Energy Accelerator Research Organization
Public Relations Office, High Energy Accelerator Research Organization (KEK), Japan
Senior Press Officer, Public Relations Office, KEK
The joint publication was completed last month. To celebrate this achievement, the first special editions of the book are presented to Drs. Cronin, Kobayashi and Maskawa today at the 50 Years of CP Violation conference held in London.
In 1993 the SLAC National Accelerator Laboratory in California and the KEK laboratory near Tokyo in Japan embarked on a quest to understand the nature of CP violation, a tiny difference between matter and antimatter that is vital for our existence. This effect was discovered in the decay of a particle called a kaon in 1964. These kaons exhibited strange behaviour compared with other particles studied at the time, and we now refer to the quark that causes that behaviour as a strange (or just s) quark. The amount of CP violation in kaon decays is insufficient to explain how the universe came to be dominated by matter.
SLAC and KEK constructed so called B Factories, which are particle accelerators and detectors to produce a large number of Bottom (or Beauty) particles, which contain b quarks, and study CP violation. The B Factory mission was to explore the phenomenon of CP violation in these particles. Twenty-one years on, these two international collaborations have come to the end of a global collaborative project: one that has produced a weighty tome over 900 pages in length, detailing all aspects of the Physics of the B Factories and their detectors: BaBar and Belle. The physics harvest from the international collaborations that run BaBar and Belle have included many notable discoveries including: CP violation in B decays, first studies of some very rare B decays, and a host of new particles. The breakthroughs have continued more recently with the determination of mixing in neutral charm mesons. This discovery paves the way for the next generation of experiments to search for certain types of CP violation in the decay of charm mesons. Almost a thousand papers have been published by these two experiments during their lifetime.
The original flagship measurements of the B Factories were found to be consistent with the Cabibbo-Kobayashi-Maskawa matrix description of CP violation. This provides the Standard Model of particle physics with a description of CP violation as predicted by Kobayashi and Maskawa in 1972.
The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
The B Factory confirmation of the Kobayashi-Maskawa mechanism was quickly followed by Kobayashi and Maskawa sharing a Nobel Prize (in 2008) for their insightful work. The Cabibbo-Kobayashi-Maskawa matrix is now known to provide the leading description of CP violation. However, while this was an important step forward for the field, the amount of CP violation in the Standard Model remains about a billion times too small to explain the matter-dominated universe that we live in. As a result the focus of the field has turned from understanding how nature behaves to the much more subtle task of trying to understand if there are small deviations from this leading description that have been missed so far.
A new book has been written as a collaboration between the two teams of physicists working on BaBar and Belle, with the help of the theory community. This is envisioned to be a pedagogical resource for the next generation of experimentalists to work in this field. Preparations started in 2008 and the concept was solidified through a number of international meetings over the past six years. This effort brought together experts from the global flavour physics communities from four continents. The KEK B Factory is in the process of being upgraded and should recommence data taking as a “Super B Factory” with a physics programme resuming in 2016. A decade from now someone will surely need to write a book on the Physics of the Super B Factory.
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