Fundamental Particles of Universe
How many different particles make up the universe and everything in it? How many remain to be discovered? Physicists are now on the edge of getting some answers to those important questions.
There are three classes of fundamental particles (particles that can’t be broken down into anything simpler): 1) leptons, 2) quarks and 3) bosons.
The most important lepton is the electron, which is found everywhere. A heavy electron called a muon doesn’t exist in nature in appreciable quantities, but it can be made in the laboratory. There is a still heavier electron called a tauon. Each of these particles has a neutrino associated with it, and all three neutrinos are different. That makes six leptons altogether.
There is also antimatter, which is just like ordinary matter but is opposite in characteristics such as electric charge. Antimatter doesn’t exist in the universe in appreciable quantities, but it also can be made in the laboratory. Antimatter is made up of six different antileptons. That makes 12 leptons and antileptons.
Quarks also come in six varieties. The most important of these are the up-quarks and down-quarks, which are the lightest ones. They make up the protons and neutrons that are found everywhere.
The heavier a particle is, the more difficult it is to form. The most massive quark, the top-quark, is 8,000 times as massive as the lightest quark; and although it hasn’t been formed yet scientists are sure that it exists. For each quark there is an antiquark, so there are 12 quarks and antiquarks altogether.
The bosons are particles that make it possible for leptons and quarks to interact with each other.
There are four kinds of interaction. There is gravitational interaction, for which there is one boson; electromagnetic interaction, for which there is one boson; weak interaction, for which there are three bosons, and strong interaction, for which there are eight bosons. That means 13 bosons altogether.
Leptons, antileptons, quarks, antiquarks, bosons--37 particles altogether. Are these all there are? Well. . . .
The most massive weak interaction boson is the Z degree particle, twice as massive as the most massive quark and first formed and observed in 1984.
A very massive particle is formed by forcing two ordinary particles together with great force. The particles smash each other into a spray of other particles. The energy of collision can be converted into a mass so that the particles formed can be much more massive than the particles that originally collided.
Currently, Carlo Rubbia is working near Geneva with the large electron positron collider (LEP). In it, a stream of electrons is whirled in a circle in one direction and a stream of positrons (the antiparticle equivalents of electrons) is whirled in the same circle in the other direction. The streams smash into each other head on and form other particles. If the energy of collision is just right, they form Z degree particles.
Construction of the LEP was begun in 1981. Electrons and positrons were passed through a circular tube nearly 17 miles in circumference. The LEP finally went into action in July 1989 and within four weeks had formed its first Z degree particle. In the United States, two different devices have been used to form them. However, the LEP has the capacity to fine-tune the quantity of energy it produces so that it is just right for Z degree particle formation. That means the LEP should produce these particles in quantity. The hope is that by the end of 1989, the LEP will have formed something like 100,000 Z degree particles.
With that many particles, it should be possible to tell how massive each particle is with greater accuracy. Then too it should be possible to tell how long the Z degree particle lasts before it breaks down. So far we know that it lasts about a millionth of a billionth of a second.
If the properties of the Z degree particle are known with proper accuracy, scientists believe they will be able to deduce just how many leptons and quarks there can possibly be. They suspect that the answer will be that there are only 12 leptons and 12 quarks possible and that all but the top-quark have been discovered.
However, even if that is so, there is still the possibility that there may be particles that are neither leptons, quarks nor bosons but that fit into different categories altogether. It may well be that the universe is far more complicated than we know.
