Beijing Spectrometer (BES)    

Beijing Spectrometer (BES) is a general-purpose detector located in the interaction region at the southern end of the BEPC storage ring, where the electron and positron beams collide.

BES is 6 meters long, 7 meters high and 7 meters wide, weighing more than 500 tons. It is mainly composed of 4 kinds of detectors and solenoids. 

BES Exterior.jpg (136705 字节)

The Solenoid.jpg (101271 字节)



Sketch Map of BES.jpg (46936 字节)

MDC in Stringing.jpg (91681 字节)

 I.  Vertex chamber, main drift chamber and electronics system

The vertex chamber is a barrel detector that is composed of 640 drift tubes with each being 84 cm long. By working together with the main drift chamber, it measures the tracks of charged particles and the momentum. It also works together with the time of flight counter (TOF) for trigger. The main drift chamber is a cylindrical detector with 20 cm in length and 220 cm in diameter, containing 10 layers of 19,380 wires and 320 channels of 320 electronics circuits.

BES general layout

 MDC in stringing

II. Time of flight counter (TOF) and electronics system

TOF contains the barrel part and the end part. The barrel part is composed of 48 plastic scintillators with each being 2.8 m long, optic fibers, photo-multipliers and electronics circuits whereas the end part is composed of 2×24 trapezoidal scintillators, optic fibers, photo-multipliers, electronics circuits, etc. It operates to measure the speed of the charged particles.

Shower Counter.jpg (113850 字节)

End Cap of Shower Counter.jpg (47158 字节)

III.  Shower counter and electronics system

The barrel part of the shower counter comprises 24 layers of counter units (13,430 in total) with each layer being 3.85 m long, and 6,721 channels of electronics circuits. The shower counter is intended for the measurement of the energy of charged particles or neutral particles.

shower counter

MDC in stringing

IV. µ Identifier and electronics system

The µ identifier is composed of 3 layers of square aluminum proportional chambers totaling 1500 with each being 4 m long and related electronics circuits. It can record the muons that have very strong penetrating ability and determine the position of bombardment.

V. Solenoid magnet

The solenoid with an outer diameter of 4 m, 3 layers of octagonal yokes and the power supplies constitute the spectrometer system that can provide a uniform magnetic field of 4000 gauss.  

Electronics System for BES.jpg (57752 字节) Luminosity Monitor.jpg (35855 字节)

VI.  Luminosity monitor

It is used to monitor the luminosity of the BEPC.

VII.  Trigger, online data acquisition and analysis, offline data analysis syetem

The fast electronics circuits are used to store large amount of data coming from the detector, and for trigger digitalization treatment.

electronics system

luminosity monitor

Institute of High Energy Physics 17/07/02