Electrons, positrons and muons are, based on solid experimental evidence, fundamental, elementary particles with no components. This is unlike the (much heavier) proton, for example, which is composed of quarks and gluons. Thus using these fundamental particles in collisions with those of equal and opposite momenta in the laboratory provides the full center of mass energy for creation of new forms of matter with well defined energy and kinematics. For this reason studies by particle physicists have called for significant investment in the enabling accelerator science and technologies that might lead to lepton colliders with TeV (Tera [10 to the power 12 ] ) electron votes) scale center of mass energies, in addition to existing proton colliders such as the Large Hadron Collider (LHC).
This project covers R&D in several of the key accelerator science and technology components of such a lepton collider; however, the results will be applicable to many existing and future accelerators of all kinds around the world. The research areas that will be pursued directly support these national priorities. Major laboratories around the world are presently conducting accelerator research and development that will lead to detailed designs of a linear electron-positron collider capable of reaching this energy range. The technology being developed for this purpose will also have applications to other areas of science and technology through new generations of intense light sources.
Note that there are two basic shapes of accelerators. Linear accelerators ("linacs") accelerate elementary particles along a straight path. Circular accelerators, such as the Tevatron and the Large Hadron Collider (LHC), use circular paths. Circular geometry has significant advantages at energies up to and including tens of GeV (10 to the power 9 electron volts) : With a circular design, particles can be effectively accelerated over longer distances. Also, only a fraction of the particles brought onto a collision course actually collide. In a linear accelerator, the remaining particles are lost; in a ring accelerator, they keep circulating and are available for future collisions. The disadvantage of circular accelerators is that particles moving along bent paths will necessarily emit electromagnetic radiation known as synchrotron radiation. Energy loss through synchrotron radiation is inversely proportional to the fourth power of the mass of the particles in question. Leptons, being light, lose a large amount of energy in this way. That is why it makes sense to build circular accelerators for heavy particles - hadron colliders such as the LHC for protons. An electron-positron collider of the same size would never be able to achieve the same collision energies. In fact, energies at the LEP lepton collider, which used to occupy the tunnel now given over to the LHC, were limited to 209 GeV by energy loss via synchrotron radiation.
As a result of previous funding the Cornell accelerator is now a flexible, unique-in-the-world test accelerator laboratory, allowing a group of scientists and engineers (with worldwide partnerships) to test and solve some of the most challenging problems faced by state-of-the-art accelerators today. These worldwide collaborations and joint efforts between labs such as those between Cornell and its extended group of colleagues and partners, and Cornell's outreach to the community, are viewed as exemplary by the community.
