By mid-afternoon on 22 November, the Belle experiment at KEK had accumulated an integrated luminosity of 500 fb-1 of electron-positron collision data. This integrated luminosity marks a landmark in the progress of the KEKB accelerator and the Belle experiment, which began operation in 1999. It is equivalent to achieving 5 × 1041 crossings of electrons and positrons a square centimetre. More than 500 million pairs of B and Bbar mesons have been generated in the collisions.
The original challenge for KEKB was to achieve 100 fb-1 in 3 years. The total of 500 fb-1 in 6.5 years surpasses this goal. The group now aims to achieve even higher records with various upgrades to the machine.
