Experimental Particle Physics Consolidated Grant 2022-2025

Fundamental physics strives to answer the big questions: what is our Universe made of; how did it evolve; what forces govern it and how do they shape the phenomena we observe? In particle physics we build experiments to examine the very smallest constituents of the Universe, fundamental particles, so that we can address these questions with our findings. Our knowledge of how fundamental particles behave is encapsulated in a theory called the Standard Model. It has enormous predictive power and provides a simple framework to understand the nature of the Universe. However, we also know the theory is incomplete. Experiments at the highest energies let us test predictions and determine the limits of the validity of our theory. Dedicated high-precision experiments let us probe predictions to incredible levels of accuracy. The faintest trace of any disagreement between theory and experimental data could provide the first hint of new laws of physics operating, which would be a step forward in understanding the nature of the Universe. One of the most pressing questions we have concerns why matter dominates so much over anti-matter. Matter and anti-matter should have been created in equal quantities in the early Universe, but very little anti-matter can be observed now. This defining feature of our Universe must ultimately be due to a difference in behaviour between matter and anti-matter, but this difference is a mystery. Neutrinos, the most elusive of particles, may hold the key to understanding why this happened. They have no charge, barely interact with matter, have a very small mass and to detect them we have had to build enormous but very sensitive detectors. An important part of our research is to make detailed measurements of neutrinos, to understand their masses and whether they are responsible for our matter-dominated universe. Another mystery we seek to resolve concerns dark matter. We know that there are not enough stars visible in galaxies to explain the speed at which stars rotate around them. We explain this by hypothesising that galaxies also contain invisible (dark) matter. Dark matter supplies the extra gravitational force necessary to keep stars in their orbits, but its nature is unknown. Many explanations have been proposed, ranging from it being formed of extremely low mass particles to massive black holes. Some explanations have been excluded, but many are extremely challenging to either confirm or reject experimentally. To address this we develop more powerful experiments using a wide range of approaches and technologies, to perform the broadest search for the unknown particles that may form this elusive dark matter.