Nearly six months ago, I penned a blog post about the Higgs boson, the final remaining undiscovered particle of the Standard Model, often referred to as the “God particle.” At the time, there was a slight bump in the data indicating that there might be hints of its discovery.
As of July 4, those bumps officially were announced to be mountains.
To explain a bit about what the Higgs is and why physicists have been searching for it for so long with no luck, allow me to rework my earlier post.
So you might be asking just what the hell is this Higgs boson anyways? How does it supposedly give everything mass? And how can scientists have searched for so long without finding it?
Well my friends, I’m here to answer those questions. And I can do it on this blog, too, seeing as how the two collaborations searching for the Higgs (ATLAS and CMS, named for the detectors searching for the particle) are so gigantic that they include scientists from every single Big 10 university, except Penn State.
I’m sure there’s a joke in there about what they’re too busy doing over in State College, but I’m not going to go there.
Or wait, I just did. Didn’t I?
Anyways, the Higgs boson is the final particle of the Standard Model that has not yet been found by particle detectors. The Standard Model is our current theory and understanding of how the universe works at the most fundamental levels. It describes each of the most fundamental particles – particles that can’t be broken down into anything smaller – and how they interact with each other to create the things we see every day.
The question up in the air is, “Why do things have mass? “ It seems like such a simple question. I mean, things just do, duh. But at the most basic levels, why do some particles weight more than others? Why is a proton 1,836 times more massive than an electron?
Currently, our best guess is the Higgs boson. Named for the theorist who came up with the idea – Peter Higgs – the Standard Model predicts that there is a massive particle permeating the entire universe in a gigantic field. I mean, these things are absolutely everywhere. But just like neutrinos, they almost never interact with the particles we can see, making them invisible and impossible to detect.
The best way I’ve heard this explained is through the metaphor of a swimming pool. Say that the Higgs field is the water and the particles of the universe are different objects moving through said water. A fish is able to move much more quickly through the pool than – say – a monster truck. Why? Because the fish interacts with the water much less. Well, the same goes for the particles of the universe. A proton interacts with the Higgs field much more than an electron or a neutrino, which gives it more mass.
Okay, but if I just said that it never interacts with normal matter and that we can’t detect it, what’s all the fuss going on over in Switzerland? Scientists can’t directly see the Higgs – assuming it exists – but that doesn’t mean that they can’t attempt to see it indirectly.
The universe is constantly changing all around us. Nuclei decay constantly, such as unstable, radioactive uranium-238 (the uranium isotope most commonly found in nature) decaying into thorium-234, which shoots off two protons and two neutrons. In fact, the radioactive decay process continues all the way through 13 more elements until it lands at the stable lead-206 – a process that takes billions of years.
Similarly, when new matter is created – which is what happens when the LHC collides two particles together – very unstable particles are often created that immediately decay into more stable ones. But unlike the elements, what particles decay into is not set in stone. Instead, there is a probability that they will decay into several other different particles.
So according to different theories, the Higgs is predicted to decay a certain percentage of the time into a certain pair of particles, which then in turn decay into more particles, and so on until they become stable. In order to search for the Higgs, scientists look for these specific decay patterns. If more of them show up than would if the Higgs did not exist, then they have succeeded in detecting its presence.
But it doesn’t end there. Depending on the mass of the Higgs, it could decay into different particles different percentages of the time. And every scientist has their favorite theory as to how big the Higgs should be. Thus, it takes a lot of people a lot of time to sift through enough data to definitely say, “No, the Higgs is not this big,” or, “Yes! There it is at this size!”
Here’s a video from Fermilab that explains all of this a little better than words can:
Six months ago, experiments had excluded territory less than 115 billion electron volts and above 130 billion electron volts. (Since E=MC^2, nuclear physicists measure mass in energy.) What’s more, both ATLAS and CMS had a bump in their data for a particular decay pattern for a Higgs weighing in between 124 and 126 billion electron volts.
But that bump in data wasn’t big enough to claim a discovery. There wass about a 1 in 20 chance at the moment that the bump in data was a statistical fluke. Scientists demand a 1 in 20,000 chance, called five sigma.
It wasn’t a statistical fluke.
Researchers, again, announced last week that their statistics had reached the five sigma level, meaning that there definitely is a previously undiscovered particle lurking at 126 billion electron volts.
Yet, the tried and true scientists will not yet claim this full discover of the Higgs. Why, you ask? Just because there’s enough data to show there is something there, there hasn’t been enough data yet to determine exactly what it is. From here on out, scientists will be searching into the new particle’s properties, in order to determine if the new particle follows the rules predicted by the Standard Model for the Higgs, or if the new particle might have some tricks up its sleeves.
If it does have some tricks up its sleeves, it would be kind of awesome. It would make scientists go back to the drawing boards to come up with new ideas for how the particle works, which is exciting.
Because hey, that’s how science works.