Hunt for the Smallest Particles

Our April speaker was Dr Peter Watkins of the School of Physics and Astronomy at the University of Birmingham who gave us a talk called "The Hunt for the Smallest Particles in the Cosmos".

Particle physicists have found that they can describe the fundamental structure and behaviour of matter within a theoretical framework called the Standard Model. This model incorporates all the known particles and the forces through which they interact, with the exception of gravity. It is currently the best description we have of the world of quarks and other particles. However, the Standard Model in its present form cannot be the whole story, for there are still missing pieces and other challenges for future research to resolve.

Scientists study atoms, nuclei and smaller particles by using very large accelerators with large detectors. An example of one of these accelerators is the Large Electron and Positron Collider (LEP) Accelerator 100 metres under the city of Geneva. It is a 27km long ring with magnets at various points, which accelerate the particles to near the speed of light in the vacuum of a tube. A particle accelerator is like a large version of the common television tube except a television tube uses a voltage in the order of 20,000 volts whereas a particle accelerator uses 100,000,000,000 volts. The electrons are introduced in one direction, while the positrons is introduced in the opposite direction. To get the required speed, smaller accelerators are used to get the speed before the particles enter the larger accelerators. There are three such accelerators at LEP, each being the predecessor of the larger versions.

As the particles are travelling in the opposite direction the magnets keep them apart, but are then used to direct the particles to collide into each other in one of the detectors. The detector then measures this impact and the resultant changes to the particles.

It is through this research that scientists have discovered all the particles in the universe have anti-particles or anti-matter but we can only see the matter.

Dr Watkins worked at LEP, which is now being replaced by the Large Hadron Collider (LHC) using the same tunnel.

Additional material to supplement this talk can be found at the following websites: