Physics & Math

The world's biggest experiment is primed to answer one of the universe's biggest questions: what is the origin of mass? But an unexpected particle could yet steal the show.

In CERN's 27-kilometre tunnel near Geneva, Switzerland, the Large Hadron Collider will start smashing high-energy protons head-on in 2010. The shrapnel is expected to reveal the presence of the one missing member of the tribe of particles predicted by the standard model of physics: the Higgs boson, which is thought to endow elementary particles with mass. But the Higgs is unlikely to emerge during the year, as its telltale traces will be hard to spot amidst the complex debris left by the proton collisions.

Instead a different particle might hog the headlines: the neutralino. No one has ever seen one, but it is predicted by the theory of supersymmetry, which fixes many problems that plague the standard model. Supersymmetry doubles the number of elementary particles, adding one heavier super-partner for each standard-model particle.

All supersymmetric particles produced in the early universe would have long since decayed into the lightest such particle, the neutralino. And the neutralino, it turns out, is a perfect candidate to account for dark matter - the mysterious stuff that far outweighs ordinary matter in the universe.

It would be easier to spot than the Higgs, and it might even make its presence felt in 2010. If it does, it would solve two problems at once: confirming supersymmetry and answering the mystery of what makes up the universe's missing mass. The Higgs would have to take a back seat.

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