Today, scientists at CERN in Geneva announced their results for their search for the Higgs boson, a subatomic particle that, if it exists, is thought to be responsible for giving other particles mass. It’s no exaggeration to call it a keystone in quantum mechanics, and finding it for sure will be a huge accomplishment for particle physicists.
So, did they find it?
Maybe. Then again, maybe not.
Um, what? OK, this’ll take a wee bit of explaining.
Last things first
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| I said Higgs, Magnum. HIGGS. |
First, the conclusion, so at least you have that in mind as you read the rest. There are two experiments running at CERN looking for the Higgs particle. They don’t smash particles together, look around with magnifying glasses and tweezers, and then yell “AHA!” when they find one. Instead, they build up a picture of it after doing gazillions of particle collisions. After a year of runs, both experiments see something that might be Higgs, but they’re not 100% sure. One sees something at about the 94% confidence level, the other at 98%. That’s pretty good, but it’s not enough to be completely sure. It seems likely they’ve found something, but it’s like a fuzzy picture: it looks like Higgs, but it still might be something else.
So why can’t they be sure one way or another?
CSI: Geneva
Basically, what the Large Hadron Collider at CERN does is whip protons around at nearly the speed of light, then smashes them into each other. At that speed they have huge energies, and when they collide that energy gets converted into matter: other particles. Like shrapnel, these new particles explode away from the collision site. Many of these new particles aren’t stable; they decay into yet lower energy particles after incredibly short time intervals. For example, electron and protons are almost certainly stable over long times (like the lifetime of the Universe), but neutrons decay after only a few minutes, turning into a proton, and electron, and a particle called an antineutrino.
So these daughter particles from the proton collisions in LHC decay, and they have daughter particles, and some of those decay, and so on. At the LHC there are two ginormous detectors called ATLAS and CMS. Both of these, in essence, measure the energy of the particles that hit them; like forensics team, they look at the aftermath of the collision and try to work backwards to figure out what happened.
We know to some extent how much energy is expected from these collisions due to all the particles that are currently known, so those can be accounted for. But if there’s some excess of energy, that could very well indicate a new particle. And we have theories as to how much energy the Higgs particle should have. So the energies are measured, calibrated for known particles, and the excesses are examined.
What both experiments found is an excess of energy — a bump in the graph — indicating a particle that has an energy* about 125 times that of a proton — right in the expected range for the Higgs particle. That’s exciting! But what they’re doing is counting up things statistically, so they can’t be 100% sure. The bump in the graph is still fuzzy.
