AQA A-Level Physics/Particles and Anti-particles/Constituents of the particle

Now, there's three types of particles, which we know about at this time, the proton, the neutron and the electron. Now, the proton and the neutron aren't what you think -- they aren't fundamental particles. Fundamental particles are particles which aren't made out of anything else, they just exist on their own. So, now we know that protons and neutrons aren't fundamental particles, what are? Well, anything which isnt made up of other particles, such as:

• Leptons (Light/small particles) such as electrons, neutrinos and muons/tauons.

What makes up the proton and the neutron?

Now, the proton and the neutrons are made up of things known as quarks and gluons. Now, the quarks are the things which carry the mass and charge of the proton or the mass of the neutron, the gluons are the things which keep the quarks in place within the particle, and they are shown as wiggly lines when drawn on diagrams.

Now, when we're looking at a proton or a neutron, we can know what kind of quarks it has in it because of the charge and masses of the individual kinds of quarks. Calculating these things arent hard because it's all just adding fractions together, which is easy. There are 6 kinds of quarks, but you'll only need to know about 3 -- up, down and strange. But, just for the sake of a rounded education, these are the full things. Dont worry about the names here, we'll go over them in a minute.

Name	Charge	Baryon Number	Strangeness
Up (u)	+2/3	1/3	0
Down (d)	-1/3	1/3	0
Charm (c)	+2/3	1/3	0
Strange (s)	-1/3	1/3	-1
Top (t)	+2/3	1/3	0
Bottom (b)	-1/3	1/3	0

Explaining the properties of quarks

Now, the first thing you'll be unfamiliar with is the term Baryon Number.This is a term thats basically either as "yes" or "no", and it's called boolean, so yes is +1 and no is 0. If there's an anti-particle, the number will be -1. Now, the other thing which we'll only go over briefly is strangeness; this is basically the time it takes for a particle to decay, which basically means, how long it takes a particle to start changing.

Now, anti-particles exist, and so do anti-quarks! They're represented with what's known as a bar, which is drawn above the shorthand name, so for instance, we have $\overline{u}$ for a u-bar, an anti-up-quark! So, let's look at how a proton is made of quarks! Lookey:

An example of calculating quarks

A proton, is made up of 3 quarks, and so is a neutron, because it's a pretty big particle in comparison to others. So, we remember from before that a proton is a baryon, and it must therefore have a baryon number of +1 and a charge of +1. So, let's start off.

$U$ = Charge of +2/3 and a baryon number of 1/3. So, we add that to:
$D$ = Charge of -1/3 and a baryon number of 1/3, so we have... $+2/3--1/3=+1/3$ charge and 2/3 charge.
$U$ = Charge of +2/3, so we add that to the +1/3 of U + D, and we get +1 (the charge of a proton) and a baryon number of +1!