One day this past December, physicist Brig Williams was waiting to hear whether he and his colleagues had helped make history. Rumors abounded that the Large Hadron Collider (LHC) had finally seen a glimpse of the Higgs boson, the Holy Grail of physics since it was first predicted by theoreticians almost 50 years ago. As one of the leaders of Penn’s team of Higgs-hunters, Williams had flown to Geneva to join a large conference of scientists at CERN headquarters.
Yet his excitement was tempered by a healthy dose of professional anxiety. Since 1994, Williams and the Penn team had been working on ATLAS (A Toroidal LHC Apparatus), designing and building vital components of its inner detector. But what if the data confirming the Higgs had come not from ATLAS but from the other major LHC detector experiment searching for the Higgs, the CMS (Compact Muon Solenoid)? After all, no one wants to be the second to make a major scientific discovery.
As it happened, the Higgs hadn’t been found—yet. But the comprehensive updates presented at the CERN council meeting made it clear that scientists were closing in on the elusive particle. Analysis of the data gathered by both the ATLAS and CMS experiments in the past year pinned down the mass of the Higgs boson, measured in gigaelectron volts (Gev), to a range of 116-130 Gev (ATLAS) or 115-127 Gev (CMS).
That crucial bit of knowledge will allow experimenters to concentrate their efforts in a narrower and more focused window, giving the Higgs less room to elude discovery. “The main message, I think, is we’re getting quite close,” Williams says. “Given that it’s almost 50 years since the Higgs particle was predicted, it’s fairly exciting.”
The last missing piece of the Standard Model of particle physics, the Higgs boson, dubbed “the God particle” by the popular press (to the consternation of most scientists), is thought to provide the mechanism by which other fundamental particles have mass. If protons, electrons, neutrons, and other particles were massless, atoms couldn’t form and the universe as we know it wouldn’t exist: “There would be no matter, no sun or earth, just a gas of particles running around at the speed of light,” Williams explains. The Higgs, however, makes it possible for particles to have mass of various precise values. “In reality, our whole world depends on these particles not only having a mass but even having the particular masses they do to a fairly accurate margin.” This makes isolating the Higgs and how it operates fundamental to understanding just why the universe is constructed the way it is. Because the Higgs decays far too quickly to be observed directly, the ATLAS and CMS experiments are designed to detect the debris of new scattered particles produced by the Higgs as it falls apart.
December’s revelations convinced Williams and most other scientists that the Higgs is finally within reach. “There’s no question that the LHC will resolve it one way or the other, and relatively soon,” he says. “I think the most likely expectation is that we have a pretty good idea by the end of 2012.”
But even with the end of the Higgs quest in sight, Williams is already looking beyond it. He says of the LHC, “I think this is by far the most exciting opportunity that I’ve seen for discovering new physics since the 1970s. The LHC is such a powerful machine and the detectors are very powerful. Theoretically we have a lot of reasons to believe that there are things beyond the standard model. It seems quite likely that we will find new phenomena within the next several years.”
