The Electro-Magnetic Calorimeter (EMC) plays an important role in the BESIII detector, whose primary function is to measure precisely energies and positions of electrons and photons.

The general physics requirements of the BESⅢ detector leading to the design of the EMC based on CsI(Tl) crystals, with the following expected performance:
(1)The energy resolution is about: 2.5%@1GeV.
(2)The position resolution for EM shower is about: 6mm@1GeV.

Construction of the EM Calorimeter

The calorimeter is composed of one barrel and two endcap sections, covering 93% of 4π. There are a total of 44 rings of crystals along the z direction in the barrel, each with 120 crystals, and 6 layers in the endcap, with different number of crystals in each layer. The entire calorimeter have 6272 CsI(Tl) crystals with a total weight of about 24 tons.

The assembly of a crystal contains the fixation of crystal and Al base, the fixation of electronics box and base-board, and the assembly of the installation splint and electronics box. The support frame of the barrel calorimeter is a slat structure and is divided into 60 (in F direction) compartments, each contains two rows of crystals (88 crystals).

Configration	Assembly	88 crystals	Support

Crystal Quality Control(processing!)

CsI(Tl) crystals from mass production should satisfy a number of requirements such as light output and light uniformity.  Each crystal is tested by measuring the position of 662 keV g ray photoelectric peak using a ¹³⁷Cs source, which get through a F3mm X 3cm lead collimated hole, at 9 points along the crystal.

The light output of a crystal is defined as the average of the 9 measurements and will be normalized to a small reference CsI(Tl) crystal. The Non-uniformity of the Light Output is defined as (S_max-S_min)/S_ave, where S_max, S_min and S_ave is the maximum, minimum and average light output of the 9 points.

Equipment	Result	Uniformity	Relative

Contact us

Lv Junguang: +86-10-88236047 lujg@ihep.ac.cn
Hu Tao: +86-10-88236064 hut@ihep.ac.cn