Western Mail Profiles: Dr Niels Madsen

‘CERN is helping us to try to solve the mystery of antimatter’

Dr Niels Madsen is a reader in physics at Swansea University and has been conducting research on antihydrogen since 2001.

DESPITE recent headlines heralding the discovery of a Higgs-like particle at CERN, the so-called standard model of physics that describes what goes on inside atoms is still considered as just a good approximation to how the universe really works.

Many mysteries remain unsolved. One of the most spectacular conundrums is why there is no antimatter in the universe. Our understanding holds that antimatter should make up half the universe and that, apart from some characteristics (for example, charge) being equal and opposite, it should be a perfect mirror image of matter.

Antimatter is, in some sense, a mirror image of matter, in the sense that antiparticles have the same or exact opposite characteristic of particles.

Antimatter consists of anti-particles in the same way as normal matter (atoms, molecules) consists of particles. A hydrogen atom consists of a proton and an electron, and its antimatter counterpart, antihydrogen, consists of a positron and an antiproton, both with the opposite charge of the electron and proton respectively.

This perfect symmetry between matter and antimatter should have resulted in the universe being symmetrical in the same way, such that equal amounts of matter and antimatter should be out there. The mystery is that this is, as far as we can tell, not the case.

Antimatter does not seem to make up any significant part of the universe today, and if it did, we wouldn’t have been around to ask questions. When matter and antimatter come into contact they annihilate and their full internal energy is released, about a factor of 100 more than the energy released in nuclear fusion that powers the sun.

This large amount of energy is one reason why antimatter is so difficult to study. As there is no antimatter in the universe it has to be made, which means that one must supply all the energy to make it, and so only tiny amounts (on the order of thousands of anti-atoms) can be made.

In our research we make antimatter atoms from scratch, namely antihydrogen, the simplest of them all. Hydrogen consists of just one proton and one electron, so antihydrogen is made up from one antiproton and one anti-electron (called a positron). Due to the energy needed to make the antiprotons the research is conducted using accelerators at CERN in Geneva.

Positrons are much less massive, and much less energy is needed, and they can in fact be collected from a radioactive source, as there are several types of radioactive decay that emit positrons.

Once the anti-atoms are made in vacuum we trap them using magnetic fields for up to 16 minutes, after which they will typically have collided with some atoms of matter that are left in our apparatus even though we try to remove them all.

We now work towards making detailed studies of the anti-atoms by measuring their structure, which may hold clues as to why antimatter had such a different fate in the evolution of the universe.

The known laws of nature predict that the two atoms should be identical, but they also leave the missing antimatter problem unresolved. By carefully comparing atoms and anti-atoms we hope to find clues to this mystery. Earlier this year we made great strides towards this goal by inducing the first ever quantum transition in an anti-atom, a feat that holds great promise for measurements to come in the next five to 10 years. Any difference found between hydrogen and antihydrogen will have profound effects on physics as we know it.

To contact Niels please email N.Madsen@swansea.ac.uk

This article first  appeared in the Western Mail‘s Health Wales supplement on 3rd December 2012, as part of the Welsh Crucible series of research profiles.