The Low Energy Antiproton Ring (LEAR) at CERN
Antimatter facilities
Low Energy Antiproton Ring (1982–1996)
Antiproton AccumulatorAntiproton production
Antiproton CollectorDecelerated and stored antiprotons
Antimatter Factory (2000–present)
Antiproton Decelerator (AD)Decelerates antiprotons
Extra Low Energy Antiproton ring (ELENA)Decelerates antiprotons received from AD

The Low Energy Anti-Proton Ring (LEAR) was a particle accelerator at CERN which operated from 1982 until 1996.[1] The ring was designed to decelerate and store antiprotons, to study the properties of antimatter and to create atoms of antihydrogen.[2] Antiprotons for the ring were created by the CERN Proton Synchrotron via the Antiproton Collector and the Antiproton Accumulator (AA). The creation of at least nine atoms of antihydrogen were confirmed by the PS210 experiment in 1995.

Experimental setup

LEAR is a multipurpose storage ring located in the South Hall of the Proton Synchrotron (PS), with a circumference of 78.5 m.[3][4] Four straight sections are alternated with compact 90° bending magnets, along with eight quadrupole doublets. The straight sections each consist of an 8m long section, where equipment such as apparatus for internal beams and electron cooling can be stored, and two short sections of 1m.[4] The C-type (bending) magnets used are open to the outside of the ring for injection and ejection.[5] The vacuum system used for LEAR is designed for baking at 300 °C.[3]

Bunches of usually a few 109 antiprotons are skimmed off the AA and then decelerated by the PS from 3.5 GeV/c to 0.6 GeV/c.[5][6] The bunch was transferred to LEAR where is could be decelerated to a minimum 100 MeV/c or accelerated to generally 1000 MeV/c.[5] For most experiments, a "beam stretcher mode" was used, where an ultra-slow extraction provided a high-duty (continuous) amount of antiprotons.[5] Another mode, "internal target", kept a beam circulating for hours, or even days, until most particles were consumed by a gas jet target.[7][5]

LEAR bending magnet quadrant

Stochastic cooling is implemented at several stages of the LEAR experimental setup, at different momenta.[5] The focus of stochastic cooling is to restrict the motion of particles in the beam and control their energies close to a certain value. From 1987, the setup included electron cooling, using the electron cooler from the Initial Cooling Experiment (ICE) to complement the stochastic cooling.[8][9] Using cooling, high quality beams at low energies and low emittances could be produced.[5]

Results

There was a total of 27 experiments performed during LEAR's 14 years of running.[10] Several meson spectroscopy experiments were setup at LEAR to analyse the rare meson resonances produced in nucleon-antiproton annilhilation.[11] These included the Crystal Barrel, OBELIX and JETSET experiments.[10] Furthermore, matter-antimatter symmetry was investigated by studying specific proton-antiproton interactions, resulting in detailed measurements of CP violation.[12] The mass difference between the proton and antiproton was also studied at LEAR with an accuracy in 1 part in 1010.[13][10]

Conversion to LEIR

In 1996, LEAR was converted into the Low Energy Ion Ring, which has since been used in the lead ion injection process for the Large Hadron Collider.[1][14] Low energy antiproton research continues at CERN using the Antiproton Decelerator. It was built as a successor for LEAR and started operation in 2000.[15]

References

  1. 1 2 "The Low Energy Antiproton Ring". CERN. Retrieved 2021-08-17.
  2. ↑ "The History of Antimatter - The Accelerator Era". 2001-02-22. Archived from the original on 2001-02-22. Retrieved 2021-08-17.
  3. 1 2 Plass, Gunther (16 May 1980). "Design study of a facility for experiments with low energy antiprotons (LEAR)" (PDF). Cern/Ps/Dl 80-7.
  4. 1 2 Lefèvre, P.; Möhl, D.; Plass, G. (1980), Newman, W. S. (ed.), "The CERN Low Energy Antiproton Ring (LEAR) Project", 11th International Conference on High-Energy Accelerators: Geneva, Switzerland, July 7–11, 1980, Experientia Supplementum, Basel: Birkhäuser, vol. 40, pp. 819–824, doi:10.1007/978-3-0348-5540-2_119, ISBN 978-3-0348-5540-2, retrieved 2023-08-07
  5. 1 2 3 4 5 6 7 Koziol, H.; Möhl, D. (2004-12-01). "The CERN low-energy antiproton programme: the synchrotrons". Physics Reports. 403–404: 271–280. doi:10.1016/j.physrep.2004.09.003. ISSN 0370-1573.
  6. ↑ Klapisch, R (1983-01-01). "The LEAR Project and Physics with Low Energy Antiprotons at CERN (A Summary)". Physica Scripta. T5: 140–142. doi:10.1088/0031-8949/1983/T5/023. ISSN 0031-8949. S2CID 250785310.
  7. ↑ Kilian, K.; Möhl, D.; Gspann, J.; Poth, H. (1984), Gastaldi, Ugo; Klapisch, Robert (eds.), "Internal Targets for LEAR", Physics at LEAR with Low-Energy Cooled Antiprotons, Ettore Majorana International Science Series, Boston, MA: Springer New York, pp. 677–690, doi:10.1007/978-1-4684-8727-5_64, ISBN 978-1-4684-8727-5, retrieved 2023-08-07
  8. ↑ Poth, H.; Schwab, W.; Seligmann, B.; Wörtge, M.; Wolf, A.; Baird, S.; Bosser, J.; Chanel, M.; Haseroth, H.; Hill, C. E.; Ley, R.; Manglunki, D.; Möhl, D.; Tranquille, G.; Vallet, J. L. (1990-02-01). "Further results and evaluation of electron cooling experiments at LEAR". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 287 (1): 328–332. doi:10.1016/0168-9002(90)91818-V. ISSN 0168-9002.
  9. ↑ Krienen, F. (1980), Newman, W. S. (ed.), "Initial Cooling Experiments (ICE) at CERN", 11th International Conference on High-Energy Accelerators: Geneva, Switzerland, July 7–11, 1980, Experientia Supplementum, Basel: Birkhäuser, vol. 40, pp. 781–793, doi:10.1007/978-3-0348-5540-2_115, ISBN 978-3-0348-5540-2, retrieved 2023-08-07
  10. 1 2 3 Bloch, Philippe (11 Jun 2012). "LEAR'S PHYSICS LEGACY". CERN Bulletin.
  11. ↑ Gianotti, P. (2005). "From LEAR to HESR: past, present and future of meson spectroscopy with antiprotons". AIP Conference Proceedings. AIP. 768: 204–208. doi:10.1063/1.1932911.
  12. ↑ Kounnas, C.; Lahanas, A. B.; Pavlopoulos, P. (1983-08-04). "Limitations on CP-violating effects in strange particle decays". Physics Letters B. 127 (5): 381–383. doi:10.1016/0370-2693(83)91022-5. ISSN 0370-2693.
  13. ↑ Gabrielse, G.; Fei, X.; Orozco, L.; Tjoelker, R.; Haas, J.; Kalinowsky, H.; Trainor, T.; Kells, W. (Sep 1990). "Thousandfold improvement in the measured antiproton mass". Physical Review Letters. 65 (11): 1317–1320. doi:10.1103/PhysRevLett.65.1317. ISSN 0031-9007. PMID 10042233.
  14. ↑ Katarina Anthony (2012). "LEAR: a machine ahead of its time". CERN Bulletin.
  15. ↑ "The Antiproton Decelerator". CERN. Retrieved 2021-08-17.


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