On 19 February the Belle experiment running at Japan’s KEKB accelerator, the KEK B-factory, accumulated a record integrated luminosity of 1 fb-1 in a single day, corresponding to roughly 1 million BBbar meson pairs.
KEKB’s design luminosity of 1 x 1034 cm2 s-1 was first reached in May 2003. Since then the record has regularly been broken and on 15 February a new peak of 1.516 x 1034 cm2 s-1 was achieved. On average the KEKB luminosity is about 20% higher than it was a year ago. During operation of the TRISTAN accelerator at KEK from 1987 to 1995, the total integrated luminosity seen by the VENUS detector was 400 pb-1. Belle is now collecting the same amount of data in less than half a day.
Most of the performance increase is due to the novel scheme of continuous beam injection used at KEKB in which the detector keeps taking data while the electron and positron beams are being injected into the accelerator. This was previously thought to be almost impossible owing to the large noise introduced by the injected beams. However, the KEK accelerator group has developed a sophisticated scheme of continuous beam injection, while the detector group has also developed an electronics system that is more tolerant to noise.
