BaBar Particle Physics Teaching Program

Introduction

Particle physics is a field of study dedicated to investigating the following fundamental questions about the composition of the universe :

What is the universe made from?

What holds it together?

Over the centuries, our answers to these questions have become more sophisticated. But the more we find out, the more there is still to be discovered ....

Atoms

The idea that the universe is made up of small 'building blocks' was first proposed by Democritus, an ancient Greek philosopher who lived from 470 to 380 BC. He called these building blocks 'atoms', a name derived from the Greek word 'atomos', which means 'indestructible particle'.

Subatomic Particles

Much later, it became apparent that atoms weren't as indestructable as had first been thought! In 1897, Thomson discovered the electron, then in 1909 Rutherford 'split the atom' in his famous Manchester experiment which demonstrated that atoms were not fundamental particles. He also coined much of the terminology used to describe later experiments, such as the term 'neutron' for the neutral particle discovered by Chadwick in 1932.

Quarks

With the advent of more and more powerful particle accelerators, hundreds of other subatomic particles were discovered. It began to look as if there must be another, even more fundamental building block of matter.

The next breakthrough came in 1964, when Gell-Mann and Zweig suggested that particles such as protons and neutrons were made up of other particles called quarks. These acquired their rather unusual name because the original theory predicted that there would be three of them, which fitted in with the phrase "Three quarks for Mr. Mark", found in Finnegan's Wake by James Joyce! (Who says that physicists don't have a sense of humour?) The quark theory has since been refined, and current experimental evidence suggests that there are six quarks. In ascending order of mass they are called up, down, strange, charm, bottom and top. (These last two were originally called 'truth' and 'beauty', but their names were changed when people decided that this was getting too silly!)