High Energy Physics (HEP) is concerned with the elementary particles and their interactions. This basic research is driven by intellectual curiosity and the desire to understand the underlying structure of the universe. Although elementary particles are infinitesimally small, the consequences of their properties are enormous. If, for example, the electron were much heavier, the universe would have evolved entirely differently: No atoms would exist, and the universe would now consist solely of electrically neutral particles.
Particle physics had relatively simple origins, beginning with the study of natural sources of particles, either radioactive atoms or cosmic rays from space. As one discovery led to another, surprises proliferated. New questions emerged, and newer and more powerful instruments were developed to answer them. Now particle physics has advanced to the point that it can ask some very deep questions:
- Can all the forces between particles be understood in a unified framework?
- What do the properties of particles reveal about the nature and origin of matter and the properties of space and time?
- What are dark matter and dark energy, and how has quantum mechanics influenced the structure of the universe?
Accelerator-based experimental HEP research, such as recently completed Large Hadron Colider (LHC) as the highest-energy particle accelerator ever built on Earth, is complemented by Astroparticle detectors which observe particles produced in space, such as:
- the flux of neutrinos emitted from the interior of the Sun, exploding stars, and colliding galaxies
- very high energy (> 100GeV) gamma-rays produced in the core of active galaxies, around pulsars and supernova remnants
- the composition of invisible dark matter (22%) and dark energy (74%) which together comprise 96% of our universe
- the origin of the highest-energy cosmic rays which generate a whole cascade of particles when they strike Earth's atmosphere.
The discoveries of HEP illuminate all of science, and the technology developed in the course of this basic research may ultimately be applied for practical benefit, as exemplified by: synchrotron type of particle accelerators which yield as a by-product intense electromagnetic radiation used in surface chemistry, materials science and engineering, environmental science, and biology; computer-aided tomography and positron-emission tomography in medical applications utilize detectors largely developed for particle physics experimentation; the World Wide Web was developed to enable elementary-particle physicists around the world to share information quickly and easily.