The current fundamental model of particle physics that explains which particles should exist and how they should behave is called the Standard Model. (We are not inventive namers in Physics & Astronomy.) However, the Standard Model, while it is fantastic at predicting many, many things, has a few glaring holes in it, which physicists are eager to either find explanations for or decide are inconsistent with observations. If they decide the latter, it means that our understanding of the universe may need to be dramatically altered.
So: we observe particles to have mass. This is one of the first things any physics course will teach you - everything has a mass. Unfortunately, the Standard Model can’t predict why any particles have mass. This is a pretty major problem! So in order to predict the existence of massive particles, it was suggested that perhaps we hadn’t found a particular particle yet; perhaps it was this unknown particle that would explain why electrons had mass. This particle was dubbed the Higgs boson, and to fix this problem with the Standard Model, it has to be found to have a set of predicted properties.
In this theory, the Higgs boson is an incredibly unstable particle that serves as a carrier of force for the more fundamental Higgs field. It’s the interaction with the Higgs field which is really what gives particles their mass. The analogy that’s commonly used is that of trying to navigate a crowded room. The people in the room are like the Higgs field, and someone that enters the room is a particle. If our field-people are just standing around, it’s pretty easy to navigate from one corner to another. Particles that can do this, without attracting the attention of the field-people in the room, have very little mass. But now imagine that you’re incredibly famous, and you walk into the room. All the people in the room will want to talk to you, and will concentrate around you. Since you’re interacting with the Higgs field extremely strongly, you have a lot of mass.
To help tell if the Higgs is a viable solution, the people at the Large Hadron Collider have been smashing protons together in the hopes of very temporarily creating one of these Higgs bosons. We can’t observe them directly, so we watch how they fall apart, and based on the energy of the pieces when it splits apart, we can figure out how massive the particle was, and if that lines up with the predictions. In July of last year, the LHC announced that they had a slight overabundance of detections at the right mass for a particle that could potentially maybe be a Higgs. Today, they announced that they were pretty sure that it was a Higgs boson of some description.
The trick is that there are also other models of the universe, beyond just the Standard Model, which predict a Higgs boson. But some of them predict very unusual particles, or multiple flavors of particle. The only way to be sure is to measure one more property of the particle - the spin. If it’s spin zero, then we found a Higgs boson that plays extremely well with the Standard Model, and there’s no reason to suspect that we have a fundamentally incomplete picture of the universe with regards to why particles have mass. If it’s not spin zero, then we’ve found a particle we were not expecting to find, and we need to figure out what it is, and where it could have come from, and why our model didn’t predict it. This is the next step for the LHC!
Have your own question? Feel free to ask!