Scientists look deeper into particles and forces in nature

A theory that describes most of the particles and forces in nature is being thoroughly explored by scientists.

epa02525016 (FILE) An undated handout released on 05 July 2010 by the European Space Agency (ESA) from the Planck telescope showing the main disc of the Milky Way Galaxy running across the centre of the picture. Astronomers around the globe were celebrating 11 January 2011 after the first results of the survey were released, with findings focusing on coldes objects in the universe. ESA said Planck has found evidence for an otherwise invisible population of galaxies shrouded in dust billions of years in the past, which formed stars at rates some 10ñ1000 times higher than we see in our own Galaxy today. EPA/ESA, HFI and LFI consortia / HA EDITORIAL USE ONLY/NO SALES *** Local Caption *** 00000402237790 02525016.jpgShow less

Prepare yourself for a major outbreak of Higgsteria this week, when scientists pop up in the media wild-eyed with excitement over the latest evidence for something called the Higgs particle.

Their excitement is understandable, given a bit of effort. The existence of "the Higgs" was first mooted half a century ago by an eponymous Scottish theorist, and is currently the leading contender for the answer to the question: why do things have mass?

Very roughly speaking, the Higgs is linked to a force-field that endows particles making up atoms with the property we call mass. As such, the Higgs is the final but vital piece of the esoteric theory describing most of the particles and forces in nature, known prosaically as the Standard Model.

Like the Loch Ness Monster, the Higgs has allegedly been glimpsed several times over the years, but the evidence has never been compelling. That is being changed by scientists near Geneva, Switzerland whose gigantic Large Hadron Collider (LHC), has the power to reveal the Higgs, if it exists. And yesterday, the teams involved were reportedly told of what their findings mean by their data analysis experts.

What they've found will become clear on Wednesday, when the latest results from the LHC are unveiled at an international conference in Melbourne, Australia.

Anyone expecting a definitive announcement of a discovery is likely to be disappointed, however. That's because the discovery of the Higgs won't take the form of some scientist holding up, say, a photographic plate with the telltale streak of light on it. In fact, the LHC can't detect the Higgs directly. Instead, its existence has to be inferred indirectly, by analysis of billions of particle tracks detected by the LHC whose appearance (or otherwise) is consistent with the existence of the Higgs.

The discovery process is thus like a police operation in which months of surveillance of suspects is used to build a case for the existence of a "Mr Big" who never appears. It's an especially apposite metaphor in the case of the Higgs, which is expected to be very hefty by the standards of particle physics, weighing in at about 125 times the mass of a proton - which is more than an entire atom of silver. This is why only a machine as powerful as the 27-kilometre long LHC is needed to create the thing, and then only for a tiny fraction of a second.

So on Wednesday the international team of "detectives" at the LHC will announce how strong a case they now have for the existence of Mr Big, together with an estimate of his mass. It's possible that the last batch of evidence, unveiled last December, has proved to be a red herring.

It is fair to say, however, that many physicists are expecting that the LHC to have built an even stronger case, although one still not quite good enough to guarantee a verdict in the Court of the Physical Sciences. For that, the evidence has to be more than just a balance of probabilities, or even beyond reasonable doubt. It has to be such that only an irrationally sceptical observer could still harbour serious doubts.

And that level of evidence may not emerge for another year or more.

Even so, we can expect plenty of excitement if this week's results suggest the LHC scientists are close to nailing Mr Big. After all, the discovery of the Higgs will complete the Standard Model, one of the greatest intellectual achievements in history.

But for all its success, the Standard Model only describes three of the four fundamental forces of the cosmos: electromagnetism, the so-called strong interaction that binds together atomic nuclei, and the weak interaction that causes some forms of radioactivity. It says nothing about the most familiar force of all: gravity. For that, one needs to go further, to create a so-called Theory of Everything, describing all of the forces and particles in the cosmos.

So when the results are announced on Wednesday, listen out for any mention of the LHC's attempts to find evidence for this ultimate theory, in the form of something called supersymmetry.

Any Theory of Everything must be able to unify the two basic types of particles in our universe: re so-called fermions, which make up matter, and bosons, which carry forces. In the 1960s, physicists were looking for ways of revealing the underlying unity of these two groups, and the Japanese theorist Hironari Miyazawa showed that a mathematical process called supersymmetry could do the trick.

His idea was overlooked for years, and supersymmetry had to be rediscovered several times before finally being taken seriously.

But like all good scientific ideas, it makes a prediction: that every fermion should have a boson "superpartner", and vice versa. These new particles are now being hunted at the LHC.

Over the past two years, the gigantic machine has blasted together protons to recreate the conditions at which the superparticles should emerge. If the basic theory is right, the first to be found will be the so-called neutralino, the lightest and most stable of all the superpartners.

Like the Higgs, it won't be seen directly. Instead, it will reveal its existence through an unexpected dip in the energy unleashed during the collisions in the LHC.

There are many theorists who would dearly like to see that blip turn up - and not just because of its support for the Theory of Everything. It may also help resolve another long-standing mystery: the nature of Dark Matter.

First hinted at more than 70 years ago, Dark Matter is now known to make up over 80 per cent of all the mass in the universe, hugely outweighing that made from atomic matter. As yet, no one has discovered from what Dark Matter is made, although theorists think the best candidate is the neutralino.

So even if the news about the Higgs is positive on Wednesday, listen out for any mention of evidence for supersymmetry. It could be the first sign that the Theory of Everything, which eluded even Einstein, may emerge during our lifetime.

Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England.