The first four paragraphs of the Wikipedia page on quarks seem decent: https://en.wikipedia.org/wiki/Quark https://en.wikipedia.org/wiki/Quark I hadn't heard o

The first four paragraphs of the Wikipedia page on quarks seem decent: https://en.wikipedia.org/wiki/Quark https://en.wikipedia.org/wiki/Quark I hadn't heard of axions before, but https://en.wikipedia.org/wiki/Axion https://en.wikipedia.org/wiki/Axion and https://en.wikipedia.org/wiki/Peccei%E2%80%93Quinn_theory https://en.wikipedia.org/wiki/Peccei%E2%80%93Quinn_theory seem to be a starting point.