A hyperon is a type of quantum mechanical particle: a fermionic and baryonic hadron with non-zero strangeness. Don't panic at that description though, all will be explained one bit at a time - but first, here's an introduction to the nature and behaviour of particles.

The Nature of Particles

A particle can exist in two forms: a wave or a point, often referred to as 'Wave-Particle Duality'. Waves are not composed of any matter whatsoever - they are simply the result of vibrations in a medium, be it air (such as sound waves) or water. Point particles are fundamental and, theoretically, have no breadth or thickness at all. The nature of point particles is under continual debate even now. Particles can be found in many places, such as within atoms, free-standing in the vacuum of space, or as carriers of a force (such as the photon, carrier of electricity and magnetism).

All electrically-charged particles have a corresponding anti-particle. Antimatter is considered opposite to matter because of its reversed electric charge, and due to the fact that when matter and antimatter meet, they will annihilate each other releasing energy in a flash of gamma radiation (an invisible high-frequency form of electromagnetic waves¹).

The Behaviour of Particles

Particles that are smaller than atoms are constantly misbehaving. They never stay in one place, or even as the same type of particle, and they tunnel from place to place without travelling in the space between. And, just like a teacher entering a room of rowdy school children, they calm down when they are observed. On observation, they suddenly retain just one identity and one location.

It probably sounds odd. How does a particle know when it has been observed? An observation does not need to be a conscious being looking at it, it can be a photon (a carrier of light) that bounces off it, taking 'information' away with it.

There are lots of different particles, and the Standard Model of Particle Physics names many of them. An example familiar to chemists and physicists are the protons and neutrons, particles inside the cores of atoms. However these particles are not fundamental, they can also be explained (which improves the consistency of experimental predictions with experiment) in terms of smaller particles, the quarks.

'Hyperon' is the name given to a certain type of particle, as a way of classification.

The Nature of Hyperons

Now that we have the basics, we can find out what hyperons, the fermionic and baryonic hadrons with non-zero strangeness, are.

We will start with 'fermionic'. If a particle is fermionic, it is one that obeys the Fermi-Dirac statistics.

Fermi-Dirac Statistics

The Fermi-Dirac statistics were calculated independently by the pioneering quantum physicists Enrico Fermi² (1901 - 1954) and Paul Dirac³ (1902 - 1984). They are rules that determine the behaviour of a limited number of quantum particles, called fermions. It states that no two identical fermions can exist in the same quantum state; if they do, then one of them instantly changes to being in the opposite state. Two particles that do this are said to be entangled.

An exemplary quantum state would be its 'spin'. 'Spin' is a loose term used by physicists with no fixed definition, pertaining to its angular momentum and symmetry, and is measured in Planck units⁴. All fermions have what is called a half-integer spin. So, if a fermion has spin 3/2 then it basically means that after rotating it one and a half times, it will look the same as its original state (this is the same as rotational symmetry). In other words, its order of rotational symmetry is 1.5.

Now, suppose another fermion exists in a distant solar system that has been struck by a powerful laser, and its angular momentum has been changed. This might mean that its 'spin' changes to 3/2. This, however, is the same as the first particle discussed above. This violates Fermi-Dirac statistics, but it does not actually matter unless one of the now 'entangled' particles is observed. At this point the second fermion need not ever have come into contact with the first, or be within any fixed distance of it, but it will always change instantaneously to a different spin. In large numbers of fermions, these statistics are crucial.

An electron is another type of fermion.

Hadrons

If a particle is a type of hadron, it simply means that it feels the strong nuclear force. This force is that which holds the central nuclei of atoms together with a range of about 10^-13cm. The strong force does this by exchanging carriers of this force between quarks; these force-carrying particles are called gluons, which is a very appropriate name. The strong force is 10³⁶ times stronger than gravity! Baryons are always composed of three quarks, which makes them a subgroup of the hadrons. Mesons are another subgroup of hadrons consisting of those made from two quarks.

Strange Particles

If a particle has a ‘non-zero strangeness’ it means that it contains one or more strange quark. Quarks come in six ‘flavours’; these flavours are just different types of quark and are called, for no particular reason: up, down, top, bottom, strange and charmed.

The Behaviour of Hyperons

So, we have now discovered that a hyperon is a particle composed of three quarks, at least one of which is strange, that must be completely unique when observed, and is affected by the strong nuclear force. Strangely, hyperons have a very short life, only staying for about 10^-10 to 10^-8 seconds before decaying into a proton, a neutron or a meson (and if it decays into a neutron, it will decay further into a proton). Hyperons are heavier than all of these.

The reason for this spontaneous eruption into gamma radiation is simply an enactment of the quantum weirdness: particles exist in a 'superposition' of states, and are quite unstable. Their whole identity hinges on probability. Imagine waking up in the morning to find that you have broken apart into two ferrets - this is the sort of thing particles get up to.

Since hyperons contain so much energy, they may travel several metres before releasing it in their decay. To be able to do this, they must be travelling at speeds close to that of light. It is this fact that makes them an object of intense research...

Discovery of hyperons happened mostly in the 1950s, and spurred physicists on to the creation of an organised classification of particles. Research into hyperons is undergone mostly at the Fermi National Accelerator Laboratory in Batavia, Illinois using particle accelerators. It is here that HyperCP experiments are conducted. These experiments test for CP Violation.

The HyperCP Experiments

Fermilab's HyperCP experiments serve to measure the decay properties of hyperons, and their antimatter counterparts called anti-hyperons, as accurately as possible. The experiments can probe the difference in the decay of hyperons and anti-hyperons down to an accuracy margin of one part in 10,000. It is hoped that if a major discrepancy is proved, it will provide evidence for a theory about symmetry violation.

Symmetry violation has been proposed by physicists such as the Russian Andrei Sakharov who feel that it may play a major role in the nature of the universe as we know it. Why? It is because the universe is composed of more matter than antimatter and nobody knows why. It suggests that the universe had some form of bias or cosmic favouritism. This fact breaks a type of symmetry that is known as CP symmetry, which is why the experiments are called HyperCP.

The experiments take several months each and are conducted by thirty-five physicists and students from nine institutions. It takes about a year for the data to be thoroughly analysed too. The particles are detected with the HyperCP spectrometer.

Solving the mystery of CP violation and why there is more matter than antimatter in the universe would be a major breakthrough. These strange particles called hyperons may indeed be the answer.