Electromagnetic Calorimeters (EB & EE)

The electromagnetic calorimeter is separated into three sections, a barrel section and two endcap regions. The barrel section is a cylindrical array of 9440 lead-glass blocks. These blocks are pointed towards the interaction region, but slightly tilted away from the exact interaction point. This orientation serves to prevent neutral particles being lost in the gaps between blocks whilst also trying to prevent most particles traversing more than one block. Each block is 37 cm deep, which is 24.6 radiation lengths, and has an approximate surface area of 10 $\times$ 10 cm. The blocks have a density of 5.54 gcm$^{-3}$ and are situated at a radius of 2.455 m from the interaction point.

The subdetector works on the principle that relativistic particles travelling through the blocks will emit $\breve{\rm C}$erenkov radiation which can be collected by photomultiplyer tubes at the end of the blocks. EB covers a polar angle range of $\vert\cos\theta\vert < 0.82$ and has a spatial resolution for a particle of, say 6 GeV, of approximately 11 mm. The energy resolution of EB in units of GeV is:

$$\frac{\sigma_{E}}{E} \simeq 0.2\% + \frac{6.3\%}{\sqrt{E}}$$ (2.1)

The endcap electromagnetic calorimeters [22] cover a polar angle range of $0.83 < \vert\cos\theta\vert < 0.95$. Each of the two EEs consists of 1132 lead-glass scintillator blocks. These blocks differ slightly from those in EB in that they have a smaller density, 4.06 gcm$^{-3}$. The blocks vary in length from 380 to 520 mm, so that they will fit around the dome shape of the pressure bell at either end of the detector. Particles traversing the blocks are presented with a minimum of 20.5 radiation lengths. The energy resolution is approximately 1% in the energy region 3-50 GeV.