We study the building blocks called elementary particles, that make up everything that we see around us. A familiar example are electrons that are responsible for electricity. A perhaps less known example are quarks and gluons that constitute neutrons and protons, from which atoms are built. All currently known elementary particles can be neatly arranged in a diagram similar to (but simpler than) the periodic table of atomic elements in chemistry.
The position of elements in the periodic table informs us about their chemical properties. Likewise, there are rules governing how elementary particles interact with each other. For example, the central element in the figure below is the famous Higgs particle, which through its interactions gives other particles their mass.
Amazingly, the Higgs particle had been predicted 50 years before its discovery when researchers realized that it was crucial for the mathematical consistency of the theory. Its experimental discovery in high-energy particle collision experiments at CERN in Geneva, in 2012, spectacularly confirmed the so-called Standard Model, which encompasses all currently known particles and interactions (except for gravity). Despite this success, many hints, for example from astrophysical observations, indicate that further particles, or perhaps even additional fundamental forces, are likely to exist. However, there are not enough clues to guide us towards how a more complete theory would look like, and so additional experimental information is needed.
Our first goal is to obtain predictions for the behavior of elementary particles from the current theory which can be tested in experiments. This allows, on the one hand, to measure fundamental constants of nature. On the other hand, deviations from the theoretical predictions may indicate new particles. Any such discovery would be a major advance in the field of particle physics and beyond, for example, for understanding astrophysical phenomena. Most importantly perhaps, it could provide hints for how a complete fundamental theory of all matter in our universe might look.
The second goal is to better understand the Standard Model at a fundamental level. The latter is formulated mathematically as a quantum field theory (QFT). It allows us to describe interactions between particles. Some of these processes are different from our everyday intuition. As Albert Einstein’s famous formula states, energy is equivalent to matter, and, therefore, the number of incoming particles may be different from the number of outgoing particles. QFT also encodes the quantum nature of (sub)atomic particles. As we know from the work of Werner Heisenberg, one cannot know simultaneously and exactly both a particle's speed and velocity.
For us, this theory is conceptually beautiful and simple, to the point that its formula can be written in a few lines. However, it is notoriously difficult to obtain quantitative predictions from it, as needed to compare to experiments.
It is curious that while the computations required to extract a physically measurable quantity from QFTs are complicated, the final outcome is often strikingly simple. This motivates us to look for an explanation. Indeed, in recent years, many novel properties of QFTs have been uncovered, such as unexpected symmetries, surprising geometrical structures, and connections to seemingly unrelated fields of mathematics. These may guide us to novel ways of thinking about QFTs, and have already led to more efficient ways of performing calculations.
There is an important interplay between the goal of better understanding QFTs, and our ability to perform calculations in them. In this way, many new ideas have found their way into practical phenomenological computations, and have transformed previously unthinkable calculations into standard research tools. At CERN, the Large Hadron Collider experiment will continue to run for at least 15 more years with 95% of data still to be collected. Our research will help to use the machine's full discovery potential. Indeed, finding new particles may be even harder than finding the proverbial needle in a haystack.
What do all these elementary particles have to do with everyday life, beyond seemingly philosophical questions? To understand that, one just needs to look at history. Basic research at a given time sooner or later turns into technology. Just think of the magnetic resonance scans, or radiation therapy for cancer. All these breakthroughs had their origin in particle physics research. Nobody could say with certainty what technological advances progress in particle physics will bring about, but it is very likely that they will deeply impact life for future generations.