One of the greatest ironies of physics is that to see the smallest things in the Universe we need huge machines. The Compact Muon Solenoid detector (or just CMS for short) is one of two extremely complex – and very, very large – pieces of equipment used by CERN’s Large Hadron Collider (LHC) in Geneva to sift through the bits of shrapnel created when packets of protons smash into each at very nearly the speed of light.
Just how big is the CMS? BABloggee Thomas Radke sent me this picture of it.
Click it to see the original 6000 pixel picture hosted at CERN. Then pick your jaw up from the floor. This monstrosity is 15 meters high – nearly 50 feet! To give you a sense of the scale here, look to the bottom of the green scaffolding on the sides, and you’ll see handrails where people can stand.
I visited the LHC a few years back, thanks to Brian Cox who brought me there for a tour and interview. This was shortly before the gigantic machine was switched on, so we went down 100 meters below the Earth’s surface to take a look. I stood off to one side of the CMS, and the scale of it was hard to grasp. It’s over 20 meters long, and weighs over 12,000 tons – 24 million pounds! A lot of that weight is from the huge slabs of iron you can see painted red.
I made a video during my LHC visit, and the CMS part is about five minutes into it.
Yeah. That’s the kind of stuff we do when we want to pry open the seams of the Universe and peek inside.
Image credit: CERN
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
|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?
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.
Speaking of the LHC, the Boston Globe’s terrific feature The Big Picture has a slew of gorgeous pictures of the Large Hadron Collider up on the site.
These images, as beautiful and hi-res as they are, still cannot convey the awesome size and scale of the LHC. It’s been a year and a half since I stood there, 100 meters below of the surface of the Earth, gawking slack-jawed at ATLAS, CMS, and the other magnificent machinery, and it almost seems like a dream to me. But then I shake out of it and remember: this is what we do, and it’s real.
Secrets of the Universe? We humans figure that stuff out over coffee. What’s next?