EMC Technical Description

The calorimeter structure consists of a stack where alternating layers of scintillating fibers of 1 mm diameter are glued inside thin grooved lead layers of .5 mm thickness.
The composite has a volume ratio Pb:scint:glue of 42:48:10 corresponding to a density of 5.0 g/cm³ and a radiation length X₀ of 1.5 cm. The final stack has a depth of 23 cm (15 X₀) corresponding to around 200 planes of lead/fibers. The chosen longitudinal dimension is enough to contain more than 98% of 500 MeV electromagnetic showers (corresponing to the maximum shower energy at KLOE).
The decision of using scintillating fibers was driven by the necessity to get an excellent time resolution for long detectors (fiber length is ranging from 2.0 to 4.3 m) given the small trapping angle of the light propagating on the fiber core. Another advantage on using fiber is that the attenuation lenght is also much better (4.5 m vs 2 m) when comparing with a scintillator slab.
The total lenght of fibers used in the calorimeter is 15000 Km!
Final fibers chosen were: Kuraray SCSF-81 and Pol.Hi.Tech.0046.
The light produced by the fiber in almost square cells (4.4x4.4 cm²) is concentrated at both calorimeter ends via Plexiglass light guides on mesh PMs (Hamamatsu R5946/01 1.5" tubes). The total number of PMs is 4880.