Nearer, my god particle, to thee


Scientists are close to finding the Higgs boson, but what is it? And, after it’s found, what next?

THIS MONTH, scientists at Fermilab in the US reported a possible sighting of the elusive entity known as the Higgs boson. The finding is not conclusive, but it complements the results announced last December at the Large Hadron Collider at Cern in Geneva. It seems the net is finally closing in on the Higgs.

What exactly is the Higgs boson?Scientists have long known that the atomic nucleus contains tiny particles of matter called protons and neutrons, themselves made up of smaller entities called quarks. The full list of the elementary particles of matter is described by the Standard Model. The Higgs particle is a key element of the Standard Model; while all other particles predicted by the model have been detected in experiments in particle accelerators, the Higgs remains outstanding.

Why is the Higgs so important?One of the great challenges of particle physics is to explain why the elementary particles of matter have the properties they do – in particular why different particles have different masses. According to the Standard Model, particles acquire mass as a result of their interaction with a certain type of quantum field, named the Higgs field after theoretician Peter Higgs of Edinburgh University. Theory predicts that if the field exists, an associated particle – the Higgs boson – should also exist.

Why is it also called the God particle?Most physicists dislike the name, but it is apt in the sense that the field associated with the Higgs particle is thought to endow all other particles with mass. Another reason is that the particle has become something of a Holy Grail in particle physics because it has proved remarkably hard to find.

How can the Higgs be observed?At the Large Hadron Collider, two beams of protons are slammed into each other at extremely high energy. Exotic particles are created out of the energy of collision, just as predicted by Einstein (E=mc2). These unstable bits of matter quickly decay into other particles, including Higgs bosons. The Higgs particles themselves then decay into lighter particles in a number of different ways. The different experiments are reporting tentative sightings of the decay products, hence the excitement.

How definite are the results?The Fermilab results could prove to be a statistical anomaly, and this is also true of the December results at Cern. However, it is exciting that four different experiments (two at the LHC and two at the Tevatron accelerator at Fermilab) are showing slight bumps at around the same energy. This result comes from groups whose work normally consists of closing windows of possibility, ie excluding mass ranges for the Higgs. Now one small window is looking very promising indeed.

How long until confirmation?The Tevatron accelerator at Fermilab is now out of commission, so it’s up to Cern. At the LHC, the energy of the proton beams will be ramped up to higher energy in order to get more precise data. This is a major technical operation that will require some months before experiments can be got underway again.

What comes after the Higgs?The LHC brings us to a new frontier because the higher the energy, the deeper we can probe matter and the forces that hold it together. Along the way, the experiments give us important insights into the very early universe because the high-energy conditions resemble those that existed when our universe was very young. In particular, physicists will search for exotic particles known as “supersymmetric” particles. The detection of these particles is an important test for unified field theories; these theories suggest that the four fundamental forces of nature once comprised a single force in the infant universe.

Will finding the Higgs have a technological application?No. However, the technologies developed in particle experiments find important application in society. A good example is the use of accelerators in modern medicine. Another is the world wide web, an early version of which was developed at Cern in order to allow scientists to share data. The latest innovation is the GRID, the networking of thousands of computers worldwide in order to facilitate the analysis of huge amounts of data emerging from the LHC.

So, an exciting discovery?It’s early days yet, but it looks that way. Within a year, we will know for sure whether the Higgs boson exists or not.

Dr Cormac O’Raifeartaigh lectures in physics at Waterford Institute of Technology