The physics world was abuzz with some tantalizing news a couple of weeks ago. At a meeting of the European Physical Society in Grenoble, France, physicists -- including some from Caltech -- announced that the latest data from the Large Hadron Collider (LHC) might hint at the existence of the ever-elusive Higgs boson.
According to the Standard Model, the remarkably successful theory of how all the fundamental particles interact, the Higgs boson is responsible for endowing every other particle with mass. And as the last remaining particle pr edicted by the Standard Model yet to be detected, its discovery is one of the chief goals of the LHC, the most powerful particle accelerator on Earth and perhaps the most complex scientific endeavor ever attempted.
Sitting underground near Geneva, Switzerland, the LHC accelerates protons around a ring almost five miles wide to nearly the speed of light, producing two proton beams that careen toward each other. Most of the protons just keep on going past each other, but a small fraction of them collide, creating other particles in the process. But these particles are fleeting, decaying into lighter particles before they can be detected. The challenge for physicists is to pick out hints of new, exotic physics from the flurry of newly minted particles. By sifting through the data, they hope to tease out signs that some of these particles are Higgs bosons.
The LHC is equipped with several detectors, but the ones that are the largest and are going after the Higgs are called ATLAS (A Large Toroidal Apparatus) and the Compact Muon Solenoid (CMS); Caltech plays a prominent role in the latter. Both experiments recently reported what physicists are calling "excess events." That is, the LHC appears to have created slightly more events than would be expected if the Higgs does not exist. The bump occurred in the region between 130 and 150 gigaelectron volts (GeV -- a unit of energy that is also a unit of mass, via E = mc2, where the speed of light, c, is set to a value of one), which is the expected mass range of the Higgs. But the data are not yet statistically significant enough to be called a definite signal, let alone a discovery of the Higgs particle, says Harvey Newman, professor of physics.
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