Top postcard from Fermilab

19 August 1998

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The image here is from one of a set of postcards produced by the Fermi National Accelerator Laboratory (Fermilab) in Illinois. It shows the decay of a top quark and its antiquark, caught in a large detector known as D0. The top quark was discovered at Fermilab in the high-energy collisions of protons with antiprotons in the machine called the Tevatron. It is by far the heaviest of the six quarks, with a mass about the same as that of an atom of gold! The image here is based on a computer reconstruction of information recorded by the many layers of the detector.

The top quark likes to decay into the next lightest quark - bottom - and a W particle, carrier of the weak force. Here a W particle from either the top quark (or the antiquark) has itself decayed into a muon (the light blue track towards top right) and a neutrino. The neutrino leaves no trace in the detector, but spirits away energy; the pink block to the right shows how much energy is missing and where it went. The bottom quark that accompanied this W has produced one of the four "jets" of particles that show up in the other coloured blocks; these indicate where a lot of energy has been deposited in the middle layers of the detector. The accompanying top antiquark (or quark) has decayed to produce the other three "jets" - one from the bottom antiquark and two from the associated W particle.

Credit: Fermi National Accelerator Laboratory

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