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.
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.
*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!