Physicists have evidence for a particle that – if true – would rock theories of how the universe works
It would seem that the biggest and most famous scientific experiment in the world, the Large Hadron Collider (LHC) in Geneva, is not the only game in town when it comes to particle physics. The Tevatron accelerator at Fermilab near Chicago is having one last hurrah before it is switched off later this year, and in doing so may have produced the discovery of a generation. But if confirmed, the one thing we know is that this is not the elusive Higgs boson.
Until the LHC was switched on, the Tevatron had held the record as the most powerful particle accelerator in the world. Just like the LHC, it earns its living by smashing subatomic particles together at close to the speed of light; in the Tevatron's case these are protons and their anti-matter particles, or "anti-protons". In doing so, the colliding particles completely annihilate each other in a burst of energy that condenses out into new ones. Powerful computers then sift through the billions of particles created to find those rare occasions when something interesting is produced.
This past week has seen the physics community abuzz with excitement over a paper published by researchers at Fermilab announcing that they have found strong evidence for a never-before-seen particle that does not fit into any of our established theories. And if you believe the hype, this means nothing less than a new force of nature to add to the four we already know about (gravity, electromagnetism and the strong and weak nuclear forces). But we physicists are a cautious bunch and no one has been popping open the champagne just yet.
The difficulty is that this possible new particle cannot be detected directly; it lives for a tiny fraction of a second before it explodes into streams of more conventional particles that can be detected and traced back to it. This is how we can say that it is not a Higgs boson, which if created would have left a calling card. On the other hand, this would-be new particle weighs as much as a Higgs and even belongs to the family of particles known as "bosons", which are responsible for the forces between all the matter in the universe. However, all the known forces have their bosons accounted for, so a new boson could mean a new force.
The excitement rests on a graph of the data taken from one of the Tevatron detectors. It contains a clear bump corresponding to the weight of the proposed new particle. Although this is strong evidence, if the particle does exist then this same bump should be seen in the data from another detector there. It would also need to be confirmed by the LHC. Nevertheless, a number of physicists have already rushed to write up papers proposing new theories to describe the particle. Some have dubbed it the Z-prime particle, others the "technicolour" boson. No doubt more exotic explanations will appear over the coming days and weeks until the evidence either gets stronger or evaporates completely.
The result has, in fact, been known for a while, but experimenters have now reached what is called a three-sigma confidence level which, translated, means they are 99.7% sure the result is genuine. Now, you might think this is good enough, but we have had false alarms before. Many "discoveries" have turned out to be mistakes in the data analysis or computer code errors. So a lot more checking is required. Most physicists are therefore excited by the news but remain sceptical. On the other hand, as Sherlock Holmes said, when you have eliminated the impossible, whatever remains, however improbable, must be the truth. Well, maybe.
Like most physicists, I remain unconvinced. I suspect this is a false alarm, but hope I am proved wrong. There is nothing more exciting in science than discovering that the way we thought the universe worked is not quite right.