CLEO (particle detector)

The CLEO experiment was a particle detector that operated from 1979 to 2008 at the Cornell Electron Storage Ring (CESR). The experiment was designed to study the exotic and short-lived particles produced when beams of electrons and their antimatter counterparts, positrons, were smashed together at high energies. Functioning like a giant, multi-layered digital camera, the detector recorded the subatomic debris from these collisions. This allowed physicists to study the fundamental building blocks of matter, particularly particles known as mesons and leptons containing bottom quarks, charm quarks, and tau leptons. The name CLEO is not an acronym; it is short for Cleopatra and was chosen to complement the accelerator's name, CESR (pronounced Caesar).

Over its thirty-year lifetime, the CLEO detector and the international collaboration of physicists who ran it made significant contributions to particle physics. The experiment's primary focus was the study of B mesons, particles whose behavior provides key insights into the universe's matter-antimatter imbalance and the weak force. While later, more powerful B-factories like BaBar and Belle eventually surpassed its capabilities in B physics, CLEO remained a highly productive experiment. In its later years, under the name CLEO-c, it shifted focus to high-precision measurements of particles containing charm quarks, providing crucial data for testing theories of the strong force. At the time of its decommissioning, CLEO was one of the longest-running experiments in the history of particle physics.