While electron accelerators can be used to study a wide variety of physics topics, the current program focuses on the study of charm and bottom quarks and the tau leptons. These particles are all heavier than what makes up everyday matter and well suited for studying rare processes, such as CP violation.
Scientists have observed CP violation in rare particle decays, containing strange quarks (K mesons) and bottom quarks (B mesons). Observations of CP violation in B mesons at SLAC and a similar accelerator at KEK in Japan have made it possible to further test the theory. This ongoing study requires both new measurements of CP violation in other B meson decays as well as measurements of other properties of particles containing bottom or charm quarks. Solving the mystery of CP violation will answer questions about whether the laws of nature are the same for matter and antimatter.
In addition to studies of CP violation, the BaBar experiment at SLAC has pursued a broad program of research on particles containing bottom or charm quarks. The Belle experiment at KEK carried out a similar program, with a small number of U.S. university researchers participating. There has been regular cooperation as well as competition between the BaBar and Belle experiments, leading to more precise measurements and a better understanding of the results. The CLEO-c experiment at the Cornell Electron Storage Ring (CESR) concentrated on certain measurements of particles containing charm quarks that are difficult to find at the SLAC and KEK B-factories. These results test theories used to interpret CP violation measurements and to provide key inputs to the physics analyses done at the B-factory.
A proposed electron-positron collider, the ILC will complement the LHC, a proton-proton collider at CERN. Consisting of two linear accelerators that face each other, the ILC will hurl some 10 billion electrons and positrons toward each other at nearly the speed of light. Stretching approximately 20 miles in length, the beams collide 14,000 thousands times a second at high energies of 500 billion-electron-volts (GeV). Each collision creates an array of new particles that could answer some of the most fundamental questions of all time. The current baseline design allows for an upgrade to a 35-mile, 1 trillion-electron-volt (TeV) machine during the second stage of the project. Several hundred U.S. scientists are making large contributions to the R&D program for the proposed next-generation collider.