Low Energy Antiproton Ring

Low Energy Antiproton Ring. It was a unique storage ring at the CERN laboratory designed to decelerate, store, and manipulate beams of antiprotons at low energies for precision physics experiments. Operational from 1982 to 1996, it enabled groundbreaking studies in antimatter physics, including the first production of atoms of antihydrogen. The facility played a pivotal role in advancing the understanding of CPT symmetry and the strong interaction by providing high-quality, low-momentum antiproton beams to experiments.

History and development

The proposal for a dedicated low-energy antiproton facility emerged in the late 1970s, following the successful operation of the Initial Cooling Experiment and the Antiproton Accumulator at CERN. Key figures like Simon van der Meer, who pioneered stochastic cooling, and Carlo Rubbia advocated for a ring capable of detailed antimatter studies. Approved in 1980, construction was completed rapidly, with the first antiproton beam stored in 1982. Its development was closely tied to the success of the Super Proton Synchrotron complex, which supplied the initial antiproton beams. The project represented a strategic shift at CERN towards precision low-energy physics alongside its high-energy collider programs like the Large Electron–Positron Collider.

Technical specifications

The machine was a circular synchrotron with a circumference of 78.5 meters, constructed in the North Area of the CERN Meyrin site. It could decelerate antiprotons from an initial momentum of 3.5 GeV/c from the Antiproton Accumulator down to 0.1 GeV/c, corresponding to kinetic energies as low as 5.3 MeV. It employed sophisticated stochastic cooling and electron cooling systems to compress the beam's phase space, achieving exceptionally high beam quality. The ring featured a straight section for internal gas-jet targets and multiple beamlines to external experiments. Its magnetic lattice was designed for slow extraction, allowing for long spills of antiprotons to fixed-target setups.

Scientific research and experiments

The facility hosted a prolific experimental program that produced landmark results in particle and nuclear physics. The PS210 experiment, led by a collaboration including Walter Oelert, famously synthesized the first nine atoms of cold antihydrogen in 1995. Experiments like PS185 conducted precise measurements of strangeness production in antiproton-proton annihilations. Studies of charmed and bottom hadrons were performed by the Crystal Barrel collaboration. Fundamental symmetry tests were a major focus, with investigations of CP violation and detailed comparisons of the proton and antiproton masses and charges to test CPT invariance. Research also extended into nuclear physics, examining antiproton interactions with nuclei.

Role in the CERN accelerator complex

Within the CERN accelerator complex, it served as a specialized user facility that received antiprotons from the Antiproton Accumulator, which was itself fed by the Proton Synchrotron and the Super Proton Synchrotron. It acted as both a decelerator and a storage ring, preparing tailored beams for its own internal targets and for external areas like the East Hall. Its operation was complementary to the contemporaneous high-energy antiproton-proton collider physics at the Super Proton Synchrotron and later preparations for the Large Hadron Collider. The expertise gained in antiproton manipulation directly influenced the design of later facilities, including the Antiproton Decelerator.

Decommissioning and legacy

The final beam was extracted in 1996, and the ring was decommissioned to make space for the construction of the Large Hadron Collider and its injector chain, specifically the Low Energy Ion Ring. Its most direct successor is the Antiproton Decelerator, commissioned in 2000, which was built to continue and expand low-energy antiproton research. The legacy of its experimental program is profound, having laid the essential groundwork for modern antimatter research. Techniques pioneered there are now standard in facilities like the Antiproton Decelerator and at the Fermilab's Antiproton Source. The first creation of antihydrogen there paved the way for subsequent precision spectroscopy experiments at CERN aiming to test the Standard Model.

Category:Particle accelerators Category:CERN Category:Antimatter