EM calorimeter vs hadronic calorimeters

[nrqed]

What is the difference between the two, in that EM calorimeter will stop photons and electrons effectively wheras hadronic calorimeters stop hadrons effectively (but both do not seem to affect much muons)? What materials are used in each type?

One usually hears that the EM calorimeters interact electromagnetically whereas the hadronic calorimeters interact via the strong force. This is misleading since charged hadrons do interact electromagnetically, of course, and the em calorimeters contain nuclei which do interact via the strong force, so what makes something a good material for use in an em calorimeter or a good material for a hadronic calorimeter?


I know that the mass must be a key factor in explaining why charged hadrons do not interact much within the em calorimeters (they must interact *some* but apparently not much) but what explains the difference of interaction between the hadrons and the EM and hadronic calorimeters, respectively?

Thanks

 

[ofirg]

The names are a bit misleading.

In both calorimeters there are electromagnetic interactions and nuclear/strong interactions.

The EM calorimeters usually have a material of high Z (Sensitive to EM interactions) and hadronic calorimters have material with High A (Sensitive to hadronic interactions). That usually makes a difference of no more than a factor 2 in that respect.

The naming really comes about form the fact that EM calorimters are designed to stop photons and electrons and prevent the EM shower from leaking into the hadronic calorimeter. These are the particles which on average loose there energy on the shortest distances. The same would be true if the hadronic calorimeter would come first.

Many hadrons still loose most of there energy in the EM calorimter via strong interactions. However, unlike photons and electrons, sometimes some of there energy leaks into the hadronic calorimeter. In that respect, the hadronic is a leakage detector. It mainly stops hadronic showers from penetrating through into the muon chambers, where a high a purity of muons can be reached,

Higher mass is the reason why charged pions and muons loose much less energy in EM interactions than electrons.

 

[mfb]

You can even build both from the same material and together - electromagnetic showers will be stopped earlier, and that part acts as electromagnetic calorimeter then. Hadrons can start their showers in the electromagnetic calorimeter, but they continue (and deposit most of their energy) in the thicker part behind - the hadronic calorimeter.

As an example:
The electromagnetic calorimeter at LHCb corresponds to 25 EM interaction lengths (=> all EM showers will be stopped within), but just 1.1 hadronic interaction lengths (many showers will start there, but deposit their energy in the hadronic calorimeter behind). The hadronic calorimeter corresponds to 5.6 hadronic interaction lengths.