| Press Release Feb. 13 |
| The KEKB/Belle experiment, which began data taking in June 1999, has logged a total integrated luminosity of about 11.2 fb-1 by the end of the year 2000. The number of recorded B-meson pairs is about 11 million. Among them, the Belle group found 325 events that can be used for the analysis of CP violations in the B-meson decays. With them, they measured the CP violation parameter sin(2phi1) to be 0.58 + {+0.32 - 0.34} {+ 0.09 - 0.10}. This result indicates that CP symmetry is violated in B meson decays at the 95% probability level. This strongly supports the Kobayashi-Maskawa theory. Although the present measurement shows a high probability for CP violation, scientifically speaking, it is not yet sufficient to claim its discovery. That will require its confirmation with a much higher level of probability. We are trying hard to increase the data sample so that we can make a much more definitive statement soon. It is noted that a similar experiment is going on at the Stanford Linear Accelerator Center in the US. At the time last Summer's conference in Osaka, the Stanford and KEK experiments presented similar results. Since then, the Stanford experiment has accumulated much more data sample than the KEKB/Belle experiment has and we are anxious to know what kind of result they are going to publicize. Future plan The observation shown today is the first page of the research; it can be said that the program has just started. It should be noted that only showing the existence of differences in decay properties between "particles" and "anti-particles" is not sufficient to prove that the Kobayashi-Maskawa theory is the single unique theory, even though this kind of observation strongly supports it. A firm confirmation of the theory will require the measurement of the six different CP-violating observables in B-meson decays and to demonstrate that they are consistent with the predictions of the theory. The measured quantity shown today is one of these six observables and this result is the first important step towards this goal. High energy physicists, including those in the KEKB/Belle group, are racing to make the most accurate measurement of these six quantities as soon as possible. We will put our best efforts to expand our measurement to the second, third, and so on, while continuing to refine our measurement of this first one. |
