  KEKB is a high luminosity e+e- collider for studying B mesons and has
achieved the design luminosity of 1034cm-2s-1 in 2003. In order to get higher
luminosity, we tested negative momentum compaction optics in the summer of
2003. We measured the bunch length using three methods at 0.7mA to 1.17mA bunch
current and confirmed the length was shortened with the negative momentum
compaction optics.
