# What exactly is measured in a e.g. hadronic calorimeter - momentum or energy of a particle?

I got a little puzzled with the concept of hadronic/electromagnetic calorimeter. Do they measure the energy of the particle e.g. an electron, like the first entry of the four-momentum, or the momentum, so the "kinetic" energy?

If I search for it in the internet, I just find, that the particles deposit their energy in the calorimeters, so it can be measured. I think, the electron e.g. cannot deposit all its energy (so the momentum and the 0.5MeV mass) because then its not there anymore and then the charge cannot be conserved.

So how can this fit together?

• Technically neither (detectors like these can only measure coarse approximations for these quantities) and usually both, in that most calorimeters these days are actually spatially resolved detectors. Part of the art of high energy physics is having to live with large compromises in resolution and precision. Even the case that a particle can not deposit all of its energy in the detector is quite common, although it's not about measuring rest mass, which is known and physically of no importance at the usual energy ranges these days. Sep 12 '15 at 16:10