Measurements of CP parameter ϕ1(β) at Belle

A precise determination of the CP parameter ϕ1(β) is the main purpose of the Belle experiment. The value was first measured for b→c transition decays and the CP violation in B meson decays was established. The measurement is now extended to b→s transition decays which are mediated by a penguin diagram. The measurement is sensitive to the existence of New Physics in the penguin loop. The results of latest measurements of ϕ1 at Belle are reported in this talk.