Colliding electrons and positrons at high energies creates heavy particles like B mesons and possibly new particles or new phenomena.

CP violation was discovered in 1964 in the decays of K mesons. This phenomenon is understood with Kobayashi-Maskawa theory, which predicted CP violation also in B mesons that contain b quarks.

The KEKB (electron positron collider) to create a huge amount of B mesons and anti-B mesons has been build at KEK and it has world's highest luminosity. At this facility, Belle experiment has been conducted to precisely measure the difference between B meson and anti-B meson decays and has already discovered CP violation in B mesons as Kobayashi-Maskawa theory predicted.

Now the successor experiment by upgrading KEKB and Belle (Super KEKB and Belle II) is ongoing. Its higher beam intensity enable us to produce much more B mesons and thus to study much more precisely.

Our group has contributed to KLM (K_L and Muon detector) and vertex detector in the Belle experiment. We also contributed the physics analysis using KLM for the discovery of CP violation and are investigating the other predictions made by Kobayashi-Maskawa theory. Tau leptons, which are created a lot as well as B meson at Super KEKB, are also to be investigated more deeply.