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Higgs bosons (like many heavy particles) decay so quickly in the detector that we only see the products of the decay. The products of Higgs decay are not unique. Depending on what its mass turns out to be, a Higgs boson might decay into two Z bosons, or two W bosons, or two b quarks, or many other particles. It may on rare occasions decay into two photons.

The image here shows the products of Higgs boson decay into two Z bosons. In this example, one Z boson then decayed into an electron and a positron (antielectron), shown as blue histograms going upwards. The other Z boson decayed into a muon and anti-muon (the red tracks).

In this event, the Higgs was produced going upwards and a jet of hadrons conserved momentum going downwards (the blue histogram followed by orange histograms). The yellow tracks are a few of the other particles produced, but have no special significance (they are a kind of background).

The histograms are the computer representations of the energy from showers of particles in the calorimeters. The blue histograms are in the electromagnetic calorimeter (which is designed for electron and photon detection), whereas the orange histograms are in the hadronic calorimeter, which is designed to detect protons, neutrons, and mesons.

Although we only see the products of the decay, we can calculate what the mass of the original (parent) particle was using the Theory of Relativity.

The decay of a fundamental particle is different from the decay of composite objects. Composite objects decay into their constituents, but fundamental particles have no constituents (that's what it means to be fundamental). They can decay into anything allowed by energy and momentum conservation and allowed by other laws of physics.

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