If the particle discovered at CERN this July is all we think it is, there are good reasons to want it to be something else
SO PETER HIGGS didn't get this year's Nobel for physics after all. It would have been the Hollywood ending to a story that began half a century ago with a few squiggles in his notebook, and climaxed on 4 July thisyear with a tear in his eye as physicists armed with a $6 billion particle collider announced they had found the particle that bears his name. Or something very like it anyway.
Higgs wasn't the only one feeling a little emotional. This was the big one, after all. The Higgs boson completes the grand edifice that is the "standard model" of matter and its fundamental interactions. Job done.
If only thingswere that simple. As particle physicists gather in Kyoto, Japan, next week for their first big conference since July's announcement, they are still asking whether that particle truly is the pièce de résistance of the standard model. And meanwhile, even more subversive thoughts are doing the rounds: if it is, do we even want it?
Higgs's squiggles aimed to solve a rather abstruse problem. Back inthe early 1960s, physicists were flushed with their ability to describe electromagnetic fields and forces through the exchange of massless photons. They desperately wanted a similar quantum theory for the weak nuclear force, but rapidly hit a problem: the calculations demanded that the particles that transmit this force, now known as the W and Z bosons, should be massless too. In reality, theyweigh in at around 80 and 90 gigaelectronvolts (GeV), almost 100 times meatier than a proton.
The solution hit upon by Higgs and others was a new field that filled space, giving the vacuum a positive energy that in turn could imbue particles with different amounts of mass, according to how much they interacted with it. The quantum particle of this field was the Higgs boson.
As the standard modelgradually took shape, it became clear how vital it was to find this particle. The model demanded that in the very early hot universe the electromagnetic and weak nuclear forces were one. It was only when the Higgs field emerged a billionth of a second or less after the big bang that the pair split, in a cataclysmic transition known as electroweak symmetry breaking. The W and Z bosons grew fat andretreated to subatomic confines; the photon, meanwhile, raced away mass-free and the electromagnetic force gained its current infinite range. At the same time, the fundamental particles that make up matter - things such as electrons and quarks, collectively known as fermions - interacted with the Higgs field and acquired their mass too. An ordered universe with a set hierarchy of masses emerged froma madhouse of masslessness.
It's a nice story, but one that some find a little contrived. "The minimal standard model Higgs is like a fairy tale," says Guido Altarelli of CERN near Geneva, Switzerland. "It is a toy model to make the theory match the data, a crutch to allow the standard model to walk a bit further until something better comes along." His problem is that the standard model ismanifestly incomplete. It predicts the outcome of experiments involving normal particles to accuracies of several decimal places, but is frustratingly mute on gravity, dark matter and other components of the cosmos we know or suspect to exist. What we need, say Altarelli and others, is not a standard Higgs at all, but something subtly or radically different - a key to a deeper theory.-------------------------------------------------
Questions of identity
Yet so far, the Higgs boson seems frustratingly plain and simple. The particle born on 4 July was discovered by sifting through the debris of trillions of collisions between protons within the mighty ATLAS and CMS detectors at CERN's Large Hadron Collider. For a start, it was spotted decaying into W and Z bosons, exactly what you would...