Bump hunters

Scientists look for evidence that two particles coalesce into a new kind of particle. Scientists expect that this particle would be observed by an unexpected bump in the expected signal (shown here in yellow).

A proton consists of smaller particles called partons. Parton is a generic term for the quarks and gluons that make up the proton. In the LHC, two protons collide. What this really means is that a parton from one proton is made to collide with a parton from the other one. Because the energy of a proton is randomly shared among its constituent partons, you can’t predict exactly how much energy will be involved in the actual collision. It’s a random process, with gentle collisions more likely than violent ones. This is, in part, because partons often have a small fraction of the proton’s energy. The low energy means collisions of low violence.

When you look at the collisions in detail, you see two different classes. In some instances the two partons just bounce off one another, similar to two billiard balls. However, occasionally the two partons will coalesce into a single object that exists for a while. The object then decays into two objects that eventually turn into the jets we observe in our detector. Jets look a bit like shotgun blasts of particles, and they represent the remnants of the objects created in the collision.

The rules of Quantum Chromodynamics govern how partons interact and make predictions on how many different types of interactions we should see (high energy vs. low energy and billiard-type vs. coalescence-type.) However, there are many new ideas predicting that collisions of certain energies are very much preferred. In these theories, two partons merge into a new kind of particle predicted by the theory. This particle then decays into jets similar to more ordinary collisions. If these particles exist, we’d see an excess of collisions at that particular energy.

CMS measured the energy of pairs of jets coming out of the collision. Unfortunately, no evidence was found to support these speculative ideas; however, as is often the case in measurements using the LHC, CMS was able to publish the most stringent limits to date.

Don Lincoln

These physicists contributed to this analysis.
Part of USCMS governance involves elected positions. These physicists were in charge of the mechanics of the most recent election.