To understand a little bit about particle physics and what is happening at the core of everything we see every day, perhaps it’s best to start at the end: the Standard Model of Particle Physics.
At its core, particle physics can be described as the study of matter (basically everything we observe and interact with everyday) and of the interactions and forces that manifest between and within matter. For centuries humanity has studied matter with great interest. Over time, our understanding has increased, and our physical models have grown better at predicting how our world works. Atomic theory, well-established for almost a century, tells us that matter is made up of atoms, which are in turn made up of smaller constituents: protons, neutrons, and electrons.
Our picture of matter has become more sophisticated since the advent of atomic theory. The most recent understanding of matter and its interactions is summarized in The Standard Model of Particle Physics. It’s here where our atomic theory becomes weirder and more wonderful. While the electron appears to this day to be a fundamental particle (that is, it has the properties of a point particle and doesn’t appear to have any deeper structure), close examination of the proton and neutron revealed they were constructed of even smaller particles. We know this because as we smash particles with more and more speed, we find out more about what’s inside. Here’s where the naming conventions get quirky (it was the 70’s after all), as these constituent particles in the proton and neutron come to be known as “up” quarks and “down” quarks (u and d in the above figure). But as you might notice in the diagram, these were not the only quarks found! Other particles were found to be made up of quarks, and soon the “strange” (s), “charm” (c), “bottom” (b), and “top” (t) quarks were also discovered. Soon, just like the atoms of atomic theory, scientists began to understand enough to start categorizing these fundamental particles in a sort of Periodic Table:
The rest of the particles along the outside of the circle (highlighted in green) are leptons, made up of the electron and its cousins the tau and the muon, and their corresponding generations of neutrinos. These are important aspects of the Standard Model, but not something I’ll go into detail to now.
These are the actors in our production; most everything we see, smell, taste, and touch is made up of these players.
What really segregates the Standard Model are interactions (forces). In some sense, these are the same forces you probably talked about in high-school physics, just at much, much smaller distances. Within the Standard Model, matter interacts through particles called gauge bosons (also known more casually as “force-carriers”). Electromagnetic interactions occur through the exchange of a photon (γ) between two particles. The other forces represented in the Standard Model are the weak nuclear force (governed by the exchange of W and Z bosons), and the strong nuclear force (governed by the exchange of a gluon, g).
But behind all of this hand-waving lie mathematical theories that have stood the test (and experiments) of time. The theory of electromagnetism is more technically referred to as Quantum Electrodynamics (QED). We can bring in the theory of the weak nuclear force and combine it with electromagnetism to get the Electroweak Theory. Finally, we have the theory describing the strong nuclear force, which is called Quantum Chromodynamics.
This is where my work lives. I study the interactions of quarks and gluons within bound states of hadrons, which is a general term for matter that is made up of quarks. It’s here where protons, neutrons, and a zoo of other particles are created.
So what’s the big deal with Quantum Chromodynamics? And how did we get to our current understanding about particle physics? Stayed tuned to find out…
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