Fitting it all together ... |
Protons are made from two up quarks and a down quark. Neutrons consist of two down quarks and an up quark. We do not see particles made from heavier quarks in everyday situations, as these are unstable, and decay into lighter, more stable, particles after a short lifetime. We can only create and observe these unstable particles at very high energies. Since energy and mass are equivalent, it is possible to give two particles extremely large kinetic energies such that when they collide then energy is converted into mass to produce a 'shower' of particles. The technical term for this is an 'event'.
There are six types of quark, but particles composed of the heavier ones can only be seen at high energies, are unstable, and have short decay lifetimes.
Practicalities |
In the early days of particle physics, photographic emulsions, then later bubble chambers and spark chambers were used to detect particles, as they left tracks behind them when they passed through. Since then, techniques have improved considerably, and fully automated electronic detectors are used in all modern experiments. Some of these can even be programmed to reject all 'uninteresting' events, so the physicists in charge waste less time!
The detection chambers are surrounded by a huge electromagnet, which exerts a longitudinal magnetic field on the particles. This causes the charged particles to follow curved paths, making it easier to identify the particles from their tracks. It also means that the momenta of the particles can be calculated, as particles with higher momenta bend less in the magnetic field.
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