Particle physics is concerned with matter, down to its smallest units and how they interact, attempting to explain the question: what the universe is made of and how does it work?
Matter
Most people will be acquainted with the atom, when it was discovered it was believed to be the smallest unit of matter. But since then it was found that the atom had smaller units inside.
Atoms have a nucleus with electrons around it. It was also found that the nucleus is made up of protons and neutrons.
For a long time protons, neutrons and electrons were thought to be the smallest unit. But even smaller units have been theorised. The trend of looking for and finding smaller and smaller units has continued for so many years. This is the Reductionist Program. People keep looking for the smallest unit and it keeps leading to smaller units. Will it stop?
For now, Yes. Nothing smaller than quarks has been accepted.
What is a Quark?
Quarks are the smallest unit of matter (that we know off). Quarks are very small, they are 1 100 000 000th the size of an atom. They make up protons and neutrons.
Three quarks make up a proton or a neutron.
A single quark has never been observed, and never will be… Quarks cannot be separated. If trying to separate quarks was attempted, more quarks would be created.
There are 36 different quarks:
| FLAVOUR |
SYMBOL |
MASS* |
CHARGE |
STRANGENESS |
BARYON NUMBER |
SPIN |
| Up |
u |
10 |
+2/3 |
0 |
+1/3 |
1/2 |
| Down |
d |
20 |
-1/3 |
0 |
+1/3 |
1/2 |
| Strange |
s |
200 |
-1/3 |
-1 |
+1/3 |
1/2 |
| Charm |
c |
3,000 |
+2/3 |
0 |
+1/3 |
1/2 |
| Bottom |
b |
9,000 |
-1/3 |
0 |
+1/3 |
1/2 |
| Top |
t |
60,000 |
+2/3 |
0 |
+1/3 |
1/2 |
*Masses are reported in terms of the electron mass, which is taken as unity.
Quarks come in 6 different "flavours": Up, down, strange, charmed, top, bottom (see table). Each "flavour" comes in three "colours": Red, green, blue. And each of these has an "anti-particle".
There is also another type of fundamental particle besides the quark, called the lepton. These too has 6 flavours: Electron, muon, tau, electron neutrino, muon neutrino, tau neutrino. And each of these has an "anti-particle", making 12 leptons in total.
So there are 36 quarks and 12 leptons, making 48 fundamental particles of which everything is made of!
Should we believe this?
So there are 48 particles, you thought that was fairly straight forward? Wait till you see how they interact!
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