Aerogel Cerenkov Counter System, ACC

Particle identification, specifically the ability to distinguish $\pi^{\pm}$ from $K^{\pm}$, plays a key role in the elucidation of CP violation in the $B$ system. An array of silica aerogel threshold Cerenkov counters has been selected as part of the Belle particle identification system to extend the momentum coverage beyond the reach of $dE/dx$ measurements by CDC and time-of-flight measurements by TOF [4,6].