Goal: To enjoy particle physics Objectives: Quarks, neutrinos, and Leptons – Oh my!

We have seen How tiny a nucleus of an atom is, but what is a single proton or neutron made out of? Lets dive in!

Contents of a proton The only thing reselbling a particle inside a proton or a neutron is a quark. A proton has 3 quarks. The quark is only 0.1 fm in size, so it does not take up much of the size. It also does not take up much of the size either. Also, the quark does not take up much of the energy (2%)

So, what makes up a proton? Well, we don’t completely know, but most of it seems to be just energy in the form of Gluons. Gluons sort of glue the quarks together. But that isn’t all. However, Gluons are really hard to observe, and everything else is even harder. So, the simple proton isn’t quite so simple, and it will be a long time before we are able to unravel what protons are really made of.

Anti-particles (antimatter) Before I talk about quarks I have to mention anti-particles. Every particle type has an anti-particle. If particle and anti-particle meet they destroy each other! They will have the same mass and energy, but opposite charge. So there are anti-protons, anti-neutrons, positrons (anti-electrons), ect.

Quarks Each proton and neutron contains 3 quarks. Any object made of 3 quarks is called a Baryon. Any object made of 2 quarks is called a Meson. Objects probably not made of quarks are called Leptons. Protons and Neutrons are Baryons. The size of a quark is about 0.1 fm. Quarks never travel alone.

Flavors of Quarks There are 6 flavors, which are vanilla, straw…. Sorry. Gen Name Sym q/e Mass / MeV·c-2 Anti 1 Up u +⅔ 1.5 – 4.0 Antiup 1 Down d -⅓ 4 – 8 Antidown 2 Strange s -⅓ 80 – 130 Antistrange 2 Charm c +⅔ 1150 – 1350 Anticharm 3 Bottom b -⅓ 4100 – 4400 Antibottom 3 Top t +⅔ ± 1800Antitop

Other Baryons 21 different known particles + their anti particles Most found in collisions of atoms in a collider or cascades in atmosphere due to cosmic rays.

Mesons Have 2 quarks. Too boring to go to it though. The most famous are the Pions

Leptons Notice I have not mentioned the electron yet. The electron is small. It is smaller than a quark. So, it probably does not have a quark. That makes it a Lepton. The other Leptons are neutrinos, Muons, and Tau particles. Neutrinos come in the flavors of all of the Lepton types (electron, Muon, Tau) Neutrinos are formed during the fusion or fission process – so we get a lot of them from the sun, but they don’t interact with matter very well so are very very hard to capture.

Other particles There are particles which exchange energy. The electromagnetic one is the photon. For the strong force there is the Gluon (which has no mass, just energy). The weak force uses quarks and leptons. The only one we don’t know about is gravity. That one is theoretically the “graviton” but it has not been observed.

Strong interaction This is the force that holds the nucleus of an atom together. If a quark gets pulled out of a proton the Gluons go with it. That causes an increase in energy which causes the formation of a pair of quarks. This gives the removed quark back to the atom it was taken from.

Conclusion In the last 100 years we have gone from barely knowing the structure of an atom to having some really cool insight as to what atoms are made of. However, this is still a lot to know and learn over the next 100 years!