Particle physicists today have a rich subatomic world to explore. They have discovered hundreds of new varieties of particle. There are pions and kaons, omegas and psis, ‘strange’ particles and ‘charmed’ ones. The members of this subatomic ‘zoo’ have been named with apparent disregard for logic. Many particles are called after letters of the Greek alphabet, and physicists habitually refer to them simply by the Greek letters. The pion, for example, is π.