Quantum Scoop

The Holy Grail of particle physics may already have been found.

Hadron collider

Some call the Higgs boson the Holy Grail of particle physics. As the only undetected element of the field’s theoretical masterpiece—the “standard model“—the Higgs guarantees a Nobel Prize for the experimenters who find it first. Now the European Union has spent an estimated $8 billion to build the world’s largest particle accelerator, the large hadron collider, to finally track it down. 

So goes the reasoning, at least, of popular science writers. In the last month, The New Yorker, the New York Times, and the Boston Globe, among others, have run articles on the LHC, which will be capable of reaching energies seven times greater than any comparable device ever created. All of this coverage has focused on the Higgs.

But what if someone else has already found it?

A rumor flying around physics departments these last few weeks claims that physicists working at the Tevatron, an accelerator located outside of Chicago, have found something new.  Originally passed by word of mouth and private e-mail, the rumor made it into the blogosphere May 28, with an anonymous comment on the blog of a particle physicist living in Venice, Italy.  Since then, the rumor has spread

This isn’t the first time a story like this has circulated. Until the LHC opens, the Tevatron remains the largest accelerator in the world. Among its most significant past discoveries is another standard-model particle, the top quark. And in 2009, it will shut its doors forever. Like the LHC, the Tevatron was built with the Higgs in mind, and as time runs out for America’s biggest atom smasher, some nervy experimentalists have jumped the gun. Last summer, two Tevatron groups released some suggestive, but fruitless, graphs (PDF), just before the International Conference on High Energy Physics; in January, a new crop of rumors emerged, which were reported in the Economist and New Scientistin March. These other rumors have described “bumps”: anomalies in the data that suggest a new particle but are too small for a definitive identification.

The current rumor, which comes in time for the summer conference circuit, may be different. It claims an experiment at the Tevatron has found a peak twice as high as the previous rumors’ bumps. And unlike the other rumors, this one includes details: the new particle’s mass, for instance, which fits within theoretical bounds on the standard model Higgs. Some versions include a decay chain, which describes what the new particle turned into as the experiment progressed, and which may be consistent with the standard model’s predictions. 

Of course, the rumor also claims that no one associated with the experiment will confirm the new findings until they’ve had time to publish, likely within the next few weeks. And until they do, no one can be certain what the Tevatron has—or has not—found.

The hype surrounding the Higgs boson is well-deserved. The standard model, a unified view of physics first presented by John Iliopoulos in 1974, describes everything we know about the smallest building blocks of nature yet observed. It’s the most accurate theory ever developed, in any field. And without the Higgs, it doesn’t make much sense: Based purely on first principles, elementary particles should be massless. Some, like photons, do have zero mass; yet others are surprisingly heavy. Enter the Higgs, which would—in theory—interact with these latter particles to make the difference.

So, if the rumor is true and the standard model Higgs has been found at the Tevatron, the LHC is in big trouble: Immediately, its “guaranteed” success—the final particle of the standard model, not to mention a couple of Nobel Prizes for European scientists—is gone.

The irony is that things look just as bleak for the LHC if the rumor is false, and the Europeans end up finding the standard model Higgs themselves. Physicists have developed such a complete description of elementary particles that, once the final piece of the theory is in place, the chances that the LHC will find anything the standard model doesn’t predict are almost negligible.

Particle theorists talk a big game. They get excited and tell reporters, not to mention government funding agencies, that the Higgs is just the beginning: The LHC, some say, may find examples of a class of particles indicative of a new fundamental property of nature, called supersymmetry. Others say there may be two or three particles, which together perform the job the standard model assigns to the Higgs. The truth is that these alternatives patch up the standard model, should something unexpected happen. If a Higgs-like particle is found, say, but it’s too light to be the standard model boson. Or if it decays in a surprising way. In cases like these, the LHC could indeed produce dramatic new discoveries.

But what happens if the Higgs turns out to be just right?  Well, then the standard model predicts that you’d need a machine roughly a quadrillion times more powerful than the LHC to find anything new.  With current technology, this would mean an accelerator the circumference of the Milky Way.  Though some theorists—proponents, for instance, of string theory—speculate about what such an accelerator might find, few other physicists take them seriously.

In fact, finding the “just right” Higgs would be bad news all around.  Surely the European Union wants more for its $8 billion than a single particle.  But more importantly, it would provide the final proof of the standard model, which happens to be clunky, boring, and infuriatingly silent on the Big Questions that the final theory of physics was supposed to answer.  Questions like: Why is there something, rather than nothing?  And where does gravity fit in?  If the standard model turns out to be a complete description of particle behavior, as the discovery of the Higgs would suggest, these questions may never be answered.

That’s why particle physicists, and the EU member states that have spent Nepal’s annual GDP to build this accelerator, are hoping that no one, in Chicago or Switzerland, finds the Higgs.  The future of high-energy physics lies with the small chance that the standard model is wrong, and something exotic happens at LHC energies. Something, I hope, that will help us understand the why questions that the standard model leaves wide open.