Backgrounder: New fundamental particle – what comes next?

Higgs boson 4 July update

CERN observes new fundamental particle – what comes next?

Both the ATLAS and CMS experiments have observed a new fundamental particle consistent with the long-sought Higgs boson. Now the exciting work of understanding its significance begins.

The results presented by ATLAS and CMS are labelled "very preliminary", having been prepared for presentation at the major particle physics conference of the year, ICHEP2012, which began in Melbourne on 4 July. The analyses are still being consolidated, and are expected to reach maturity by the end of the month. Once that has been achieved, work on determining the precise nature of the particle and its significance for our understanding of the universe can begin in earnest. In particle physics parlance, strong evidence means that the probability of an observation being attributable to a statistical fluctuation is less than one per cent. Today, both the ATLAS and CMS experiments are beyond the level of around one per million that's required to claim a discovery, and the experiments should confirm that level of confidence once these analyses are complete.

The hunt for the Higgs particle has long been one of the top priorities for particle physics. The Higgs is associated with a mechanism proposed in the mid-1960s to explain why one of nature's fundamental forces has a very short range while a similar force has infinite range. The forces in question are the electromagnetic force, which brings light to us from the stars, carries electricity around our homes, and gives structure to the atoms and molecules from which we are all made, and the weak force, which drives the energy generating processes of the stars. The electromagnetic force is carried by particles called photons, which have no mass, whereas the weak force is carried by particles called W and Z that do have mass. Rather like people passing a ball, interacting particles exchange these force carriers. The heavier the ball, the shorter the distance it can be thrown; the heavier the force carrier, the shorter its range. W and Z particles were discovered at CERN in the 1980s, but the mechanism that gives rise to their mass remains to be unlocked, and the Higgs boson is the key.

A simple observation is not enough, however, because the Higgs boson can take many forms. In its basic incarnation, the mechanism is the simplest theoretical model that accounts for the mass difference between photons and W and Z particles, and for the masses of other fundamental particles. But there are other formulations of the mechanism linked to theories such as supersymmetry, which could account for the universe's mysterious dark matter, or to theories predicting extra dimensions of space, which, if verified, would truly revolutionise our understanding of the universe we live in.

So once the discovery is confirmed, the next question is: "What kind of Higgs boson do we have"? Positive identification of the new particle's characteristics will take considerable time and data. It's rather like spotting a familiar face from afar; closer observation might be needed to tell whether it's an old friend who loves coffee, or her identical twin sister who favours tea. But whatever form the Higgs particle takes, our understanding of the universe is about to change.

ENDS

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