• Question: In your particle physiscs timeline there are many types of particle, what are the differences between them? e.g. the difference between a gluon and a tau particle.

    Asked by merikshadow to Ben on 23 Jun 2010 in Categories: .
    • Photo: Ben Still

      Ben Still answered on 23 Jun 2010:

      In one sentence: The differences are their mass and which forces they take part in (or transmit).

      The long explanation:

      There are lots of names here which are just names so stick with me. I will put them all in quote ” ” marks. Look back at where I put the timeline and you should see a figure I drew to aid the explanation (it won’t let me put it in this answer).

      There are just 12 “fundamental particles”, lego blocks if you like, from which all visible matter in the Universe is created. And then there are 4 force carrying particles, that transmit forces between the other 12.

      There are 3 forces that we care about on the atomic scale.

      The first, which we can also experience on a large scale, is the electromagnetic (EM) force. Because particles have a charge (the ability to interact with the EM force) the transfer electricity and are effected by magnetic fields. The EM force is carried by photons (denoted by the Greek letter gamma) which are particles of light.

      The “strong force” is responsible for keeping all of the positive protons together in the nucleus (along with neutrons) from flying apart (from EM repulsion).

      The last force is the “weak” force, which is responsible for most radioactivity, such as beta decay.

      The 12 “fundamental particles” are split into 3 “generations” each with 4 particles each. The only difference between the “generations” is that they get heavier, larger in mass, from 1 through to 3.

      The 4 particles in each “generation” are split into 2 types called “quarks” and “leptons”.

      The 2 “quarks” in the first “generation” make up “protons” and “neutrons” which you find in the centre, nucleus, of an atom. Quarks feel all three of the atomic forces.

      You will know one of the “leptons” in the first generation; the “electron”. They are found around the nucleus in normal atoms and provide us with Chemistry! These charged leptons feel the EM force and the weak force. The quarks and charged leptons are of similar mass.

      The second lepton is the corresponding “neutrino”. The neutrino is the lightest of the particles, each of them expected to have a mass about a million times less than the electron.

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