2004/11/10 by I. I. Bigi, Bigi, I. I.
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #hep-ph
paper · pdf · doi:10.48550/arxiv.hep-ph/0411138
22 pages, LATEX, 2 Figures; to appear in the the proceedings of `Time and Matter -- An International Colloquium on the Science of Time', Venice, Italy, August 11-17, 2002
arxiv created 2004/11/10 · arxiv updated 2009/12/01
After briefly explaining the special role played by violations of CP and T invariance and their connection with the baryon number of the Universe, I sketch the history of CP violation studies since its totally unexpected discovery in 1964. For about 30 years CP violation could be described by a single number; this has changed dramatically in the years around the turn of the millenium: (i) The existence of \em direct CP violation was unequivocally established in the decays of long lived kaons. (ii) For the first time CP violation was observed in a system other than that of neutral kaons, namely in B→ ψKS. The findings are in impressive agreement with the prediction of the CKM ansatz, which thus has been promoted to the status of a tested theory. These new insights were made possible by close feedback between theory and experiment as well as advances in detector design and a novel machine concept, namely that of an asymmetric collider. We also have direct \em experimental evidence that the observed CP violation in KL and B decays is matched by a violation of microscopic time reversal violation, as required by CPT symmetry. More recently CP violation has been observed also in B→ π+π- and B→ K∓π±. A few comments are added on subtle aspects of direct CP violation. While we know that the CKM dynamics are irrelevant for generating the baryon number of the Universe -- i.e. hitherto unknown forces have to be driving it -- we have also learnt that such `New Physics' is likely to contain CP violation of sufficient strength.