As the rumors hinted all week, this morning (9 AM Central European time, so 3 AM US Eastern time) researchers at CERN announced the discovery of a new particle with a mass of around 125 GeV. (1 GeV = 1 billion electron volts. Particle physicists often use energy units for mass, thanks to Einstein’s famous E = mc2 equation. Electron masses are about 0.5 million eV, and protons are about 940 million eV.) This is consistent with earlier data, but with far more confidence. Results from four different detectors—CDF and DØ at Fermilab, and ATLAS and CMS at CERN—all show the presence of a particle whose mass is about 133 times greater than a proton’s mass. Based on the data, the particle is a scalar particle, electrically neutral, and rapidly decaying, which are all indicative of the Higgs boson.
Is it the Higgs boson? That’s a surprisingly complicated question! The difficulty lies with our theories of fundamental particles: the Standard Model and its modifications (including supersymmetry). None of these theories provides a clear, precise prediction for the mass of the Higgs boson, and the mass ranges may overlap between different models. Some models predict the existence of more than one Higgs particle, so if any of those are true, then we have at best found a Higgs boson. And that doesn’t rule out the (slim) possibility that this discovery is a Higgs-mimic, a particle that acts kind of like the Higgs, but doesn’t play the same role. In other words, the work isn’t done.
However, my suspicion—and I’m hardly alone in this—is that this is the Higgs, or at least a Higgs. ATLAS and CMS will continue to gather data, with all eyes on that spot in the mass spectrum. If this particle continues to look Higgsian, then we’ll be able to declare 2012 as the end of the long hunt…but the beginning of a greater search, as The Hobbit is the prelude to the greater epic The Lord of the Rings. After all, we know the Standard Model isn’t all there is: there’s dark matter still to find, possibly supersymmetry, possibly things not yet predicted by our current theories.
So, let’s celebrate Higgsdependence Day, cheer this remarkable accomplishment, and acknowledge the thousands of scientists who made it possible. At the same time, let’s keep our eyes pointed ahead, not backward.