What are Quarks?


To start with, there are six types of quarks (plus their six antiquarks), which are coupled into three pairs. They are the up-down, the charm-strange, and the top-bottom (sometimes known as truth-beauty). Another interesting fact about quarks is that you can never find one by itself, as they are always with other quarks arranged to form a composite particle. The name for these composite particles is "hadrons". Quarks, like protons and electrons, have electric charge. However, their electric charges are fractional charges, either 2/3 or -1/3 (-2/3 and 1/3 for antiquarks), and they always arrange to form particles with an integer charge (ie. -1, 0, 1, 2...).


Flavour Mass
(GeV/c2)		 Electric Charge
(e)
u up 0.004 +2/3
d down 0.08 -1/3
c charm 1.5 +2/3
s strange 0.15 -1/3
t top 176 +2/3
b bottom 4.7 -1/3


Because quarks join with eachother to form particles with integer charge, not every kind of combination of quarks is possible. There are two basic types of hadrons. They are baryons, which are composed of three quarks, and mesons which are made up of a quark and an antiquark. Two examples of a baryon are the neutron and the proton.


The proton is composed of two up quarks and one down quark. As you can see, when the charges from the individual quarks are added up, you arrive at the familiar charge of +1 for the proton.


The neutron is made up of two down quarks and one up quark. Again, adding the charges from the quarks up, we arrive at zero.


An example of a meson is the pion. It is composed of an up quark and a down antiquark. Because mesons are a combination of particle and antiparticle, they tend to be very unstable and decay very quickly.

So we've now talked about quarks, but there is still the other family of elementary particles to talk about, the "leptons", which we will now discuss.