Introduction

Electrons, photons and hadrons will be stopped by the calorimeters allowing their energy to be measured. The first calorimeter layer is designed to measure the energies of electrons and photons with high precision. Since these particles interact electromagnetically, it is called an electromagnetic calorimeter (ECAL).

The event display on the right shows a simulation of the two-photon decay of a 130 GeV Higgs boson in CMS. The two photons are not seen in the tracker (inner part) but deposit their energy in the ECAL (seen as the red "blocks")

Particles that interact via the strong interaction, hadrons, deposit most of their energy in the next layer, the hadronic calorimeter (HCAL). Neutrinos escape direct detection but their presence can be inferred as an apparent energy imbalance in a collision.

The event display on the left shows a simulation of a 180 GeV Higgs boson decaying to two Z bosons, which in turn decay into two electrons (seen as red blocks in the ECAL) and two hadronic jets - seen as blocks in the HCAL

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