DIRAC – DImeson Relativistic Atomic Complex

Pions and the strong force

DIRAC is an experiment to help physicists gain a deeper insight into the fundamental force called the strong force. This plays a crucial role in particle physics, as it binds together particles called quarks, which in turn make up many other particles, including the protons and neutrons that form the nuclei of ordinary atoms.

Relatively little work has been done at low energy to test the quantum theory of the strong force, or, equivalently, how the force behaves at longer distances.

DIRAC, a collaboration of 87 scientists from 7 countries, aims to address this gap by studying the decay of unstable ‘pionium atoms’. These are transient atoms in which positive and negative pions (unstable fundamental particles made of quarks) are bound together. They are produced using a beam from CERN’s Proton Synchrotron accelerator. Their ‘lifetime’, from creation to the end of the decay process, is being measured to a level of accuracy never achieved before.