What's in a Name?
It's sometimes confusing: our field goes by two names. Both carry different connotations, but both are used interchangeably. High Energy Physics (HEP) is perhaps the more common reference and clearly denotes the idea that the highest energies of particle beams (protons, electrons, neutrinos, etc) are a tool. It's confusing because sometimes it's actually the highest intensities that are the important feature. Often, one will have whole academic groups referred to as the "High Energy Physics Group"...check out your alma mater's physics department web site! The other name is Elementary Particle Physics, (EPP) which is perhaps more general. It refers to the actual focus of the physics investigation: those bits of matter/energy which are most fundamental – elementary. For historical reasons, the two U.S. government agencies most involved with this research refer to the field by these two names. The Department of Energy has an Office of High Energy Physics, while the National Science Foundation has the Program of Elementary Particle Physics.