School of Physics Experimental Particle Physics

KEK and KEKB

The home of the Belle experiment

The Belle detector is is located at the High Energy Research Organisation (KEK) in Tsukuba, Japan. There are two major accelerators at KEK including the KEKB electron-positron collider on which the Belle Experiment is running. This accelerator is an asymmetric collider with a centre of mass energy of 10.58 GeV, an energy equal to the mass of a particle called the Upsilon(4S).

The KEKB accelerator is made up of two rings (one for the electron beam and one for the positron beam) of circumference 3016m. The Belle experiment is located at the point where the beams cross, called the interaction point. The electron beam is accelerated to an energy of 8 GeV while the positron beam is only accelerated to 3.5 GeV in order to create an asymmetry at the interaction point. This means that when the electrons an positrons collide, they will still be moving in the same direction as the electron beam with a Lorentz boost of 0.425, or at 0.425 times the speed of light. As a result time travels more slowly for the short-lived particles, giving us more time (1.22 times the time) to observe them before they can decay.

The luminosity of a particle accelerator is basically the number of interactions that happen at the interaction point per unit time. It is desirable for this number to be large, as more interactions means more data to be gathered, and so more statistics to measure. KEKB is currently the world's highest luminosity machine holding the world record of an impressive 2.11 x 10^34/cm^2/sec since June 2009.

See also:

The KEK homepage

top of page