Welcome to the Belle II Experiment

In the big bang, matter and antimatter should have been created in equal amounts. But why is the universe today filled almost only with matter? Physicists attribute the different behaviour of matter and antimatter to the violation of the so-called CP symmetry. This fundamental symmetry of nature states that laws of physics should not change when a particle is interchanged with its antiparticle and the signs of all its spatial coordinates are flipped. Still, the extent of the observed CP violation is not sufficient to explain the actual excess of matter in the universe. The Belle II experiment at the SuperKEKB accelerator in Japan aims to solve this great mystery of particle physics.

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The Detector

The new SuperKEKB accelerator and the large detector Belle II constitute a milestone in the investigation of the matter excess (CP violation) in the Universe.

In SuperKEKB, bunches of particles of matter (electrons) and their anti-particles (positrons), with energies up to 8 giga electron volts, are brought to collision at rates which are 40 times larger than in the previous KEKB accelerator. The particles being created in the collisions and the decay products formed are measured and analyzed in the Belle II experiment.

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