50 years from the Discovery of "CP-violation"

- Belle and Babar complete the Joint Book on their experimental work to prove the Kobayashi-Maskawa theory of CP-violation -

July 11, 2014

Joint publication of Belle and BaBar has completed last month. To celebrate this achievement, the first special editions of the book are presented to Drs. Cronin, Kobayashi and Maskawa at the conference held in London.

(Report from the Organizers of the conference, 50 YEARS OF CP VIOLATION)

Beauty is in the eye of the beholder

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 are still publishing new results. One special publication is the result of a global collaborative project: This 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 so far.

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 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.

The 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 two experiments are still actively publishing results, and 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.

During the celebration of 50 years of CP violation held at London at Queen Mary University of London, copies of this book were presented to Nobel laureates Cronin, Kobayashi and Maskawa (in absentia).

[Last updated: July 14, 2014]

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Related Link

Belle Collaboration
Belle ll Collaboration
The BaBar Experiment

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