What the heck is a boson?

Particles are strange. In more than one way: for example they behave as if they were spinning, like a top. But they aren’t moving at all. Even if they were, trying to imagine how some of them “spin” would probably melt your brain. The property that measures this “spinning” (though nothing is moving at all here!) is, creatively, called spin.

Some particles behave the same way no matter how you rotate them, they have spin 0. Some others look different if you rotate them, but will come back full circle after… well… a full circle turn: they have spin 1, like a spinning top. Some others come back the same after just half a turn (so not at all like a spin): they have spin 2. And so on.

The sphere on the left doesn’t change, no matter how much you turn it, like a spin 0 particle. The middle one is the same if you give it a full turn, like spin 1. The one on the right comes back after just half a turn, like it had spin2

Some particles have an additional coat of weird: they come back only after two full turns, they have spin 1/2. All the electrons, all protons and neutrons in all the atoms, indeed indeed all the quarks anywhere in the universe have spin 1/2.

These particles are called fermions, because Enrico Fermi was one of the people who described how they behave. Quantum mechanics dictates that no two fermions can be in the same exact same quantum state. This rule is called the exclusion principle, it’s what keeps atoms from melting into chaos. Ultimately, the exclusion principle is the thread suspending our universe’s order over an abyss of indistinguishable particles.

You could call this a fermion-based source of boson radiation. Credit: pexels/pixabay

Particles of integer spin (0, 1, …) don’t have to deal with this nuisance. They can traverse the quantum world oblivious of what their siblings do. All photons (spin 1) coming out of an ideal laser at the same time would be in the exact same quantum state.

Photons don’t usually come out of a laser exactly at the same time, and they are not exactly at the same place. But in principle they could be in the exact same place. Electrons couldn’t CC-BY-SA Andrea Pacelli/flickr

They are called bosons in honor of the work of Satyendra Nath Bose, who worked on describing them. Their job is hitting particles, to make them “feel” some fundamental interaction. Photons carry electromagnetic interactions, the Higgs boson carries the Higgs mechanism, which gives particles their mass, as Dr. Don Lincoln from Fermilab explains more in detail (though the video is a little dated).

If, instead of interacting with one of these so-called “fields”, particles interact with each other, they exchange short-lived “virtual” bosons, but that’s another story. So, if you’re wondering, you are 0% bosons.

If you want more
  • The great Veritasium made a nice video with an explanation of how spin actually works

Cover photo: CC0 Pexels/Pixabay

How do physicists find particles?

If you heard the news this summer that CERN actually didn’t find the particle they thought they saw, you may have realized the whole process is quite obscure. Some time ago, Abstrusegoose (rest its soul) put together this hilarious strip, that is kind of illuminating on how high energy physics works.

It’s a tad fuzzy on the details, but the basic process is the same*, just with protons (or other particles) instead of frogs. In short: you smash them real hard into each other and see what comes out.

Protons and frogs have several key differences, two of which are crucial for us. First: a proton is not a solid object, there is nothing really inside it. Second, if we put back the pieces of the two frogs we would get back two frogs. Nothing less (if we’re really good at not missing pieces), but most definitely nothing more. For particles that is very much not the case.

Accelerators like the LHC push particles very close to the speed of light. Because mass can turn into energy and vice-versa, the formidable energy released when the particles collide can produce all sorts of exotic particles that were not there before. And they can be more massive than the stuff we started with: the faster the particles, the more massive stuff can be “created”. The famous Higgs boson, for example, was discovered colliding protons, but it’s about 60 times more massive. It’s as if the collision of two frogs produced something the size of a 3rd grader.

However, it’s impossible to directly see these new particles, partly because of their very short lives. Much less than a billionth of a second after the collision that created them, they decay, shooting photons and small particles every which way.

You know those pretty pictures with all the colored lines that particle labs put out? Thelines are the trajectories of this debris shooting out of the collision.

alice-proton-lead

Credit: home.cern

And that’s the stuff physicists actually look at. There are detectors all around the collision point to measure and track and count how much of what sort subatomic junk came out and where it went. Knowing what each particle is expected to decay into, scientists can then sort through the debris and figure what happened.

If too much or too little of something comes out, it can mean that a new, unknown particle formed in the collision, which is why everyone got excited over CERN data late last year. Or it could mean that the models that tell us what to expect are wrong, which is still interesting. Or it could mean that usual particles just happened to decay more often in a particular way. This was the case with the CERN data: looking at more collisions, the averages eventually reverted to normal. No new particle for us.

 

Cover photo: LHC, CC-BY-NC-ND UCI UC Irvine via Flickr. Some rights reserved.

*Pedantic watch: I know the frog accelerator is not a collider, and LHC doesn’t quite work that way. On the other hand, that’s close enough: he’s also using frogs!