The mainframe of Beijing Spectrometer III (BESIII)?痵 Mechanical System, a major technical upgrading project costing RMB 640-million for the Beijing Positron and Electron Collider, has been completed and passed a verification check recently. As a large probe on the Collider, BESIII is designed to meet the needs for calculating high speed operation of the upgraded Collider, in an attempt to raise the measuring accuracy and reduce systematic errors. BESIII is made up of an accuracy tracking chamber, NaI crystal energy detector, and flying time calculator. The mechanical system will be used in detecting high energy particle events, collecting and amplifying signals, and accurate measuring of physical parameters.  

Started from April 2004, the efforts for upgrading the Beijing Positron and Electron Collider is scheduled to last for 5 years, in an attempt to keep a leading position among its counterparts in the world. Once it is completed, the Collider will become one of the most advanced dual-ring accelerator in the world.  The upgrades in phase I, including a linear accelerator, transformation of the colliding zone, and expansion of the transformer, have been completed, with others under construction as scheduled. According to plan, BESIII will be completed of its construction in March 2007, before connecting to other parts of the collider.