Physics:SuperKEKB

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SuperKEKB[1] is a particle collider located at KEK[2] (High Energy Accelerator Research Organization) in Tsukuba, Ibaraki Prefecture, Japan. SuperKEKB collides electrons with positrons at the centre-of-momentum energy close to the mass of the Υ(4S) resonance making it a second-generation B-factory for the Belle II experiment. The accelerator is an upgrade to the KEKB accelerator, providing approximately 40 times higher luminosity,[3] due mostly to superconducting quadrupole focusing magnets.[1] The accelerator achieved "first turns" (first circulation of electron and positron beams) in February 2016.[4] First collisions occurred on 26 April 2018.[5] At 20:34 on 15 June 2020, SuperKEKB achieved the world's highest instantaneous luminosity for a colliding-beam accelerator, setting a record of 2.22×1034 cm−2s−1.[6]

Description

The SuperKEKB design reuses many components from KEKB.[1] Under normal operation, SuperKEKB collides electrons at 7 GeV with positrons at 4 GeV[3] (compared to KEKB at 8 GeV and 3.5 GeV respectively). The centre-of-momentum energy of the collisions is therefore at the mass of the Υ(4S) resonance (10.58 GeV/c2).[7] The accelerator will also perform short runs at energies of other Υ resonances, in order to obtain samples of other B mesons and baryons.[1] The asymmetry in the beam energy provides a relativistic Lorentz boost to the B meson particles produced in the collision. The direction of the higher-energy beam determines the 'forward' direction, and that affects the design of much of the Belle II detector.

As with KEKB, SuperKEKB consists of two storage rings: one for the high-energy electron beam (the High Energy Ring, HER) and one for the lower energy positron beam (the Low Energy Ring, LER). The accelerator has a circumference of 3016 m with four straight sections and experimental halls in the centre of each, named "Tsukuba", "Oho", "Fuji", and "Nikko".[3] The Belle II experiment is located at the single interaction point in Tsukuba Hall.[8]

Luminosity

The target luminosity for SuperKEKB is 6.5×1035 cm−2s−1, this is 30 times larger than the luminosity at KEKB.[9] The improvement is mostly due to a so-called 'nano-beam' scheme, originally proposed[10] for the cancelled[11] SuperB experiment. In the nano-beam scheme at SuperKEKB, the beams are squeezed in the vertical direction and the crossing angle is increased, which reduces the area of the crossing.[1] The luminosity is further increased by a factor of two, due to a higher beam current than KEKB.[1] The focus and crossing angle is achieved by two new superconducting quadrupole magnets at the interaction point[1] that were installed in February 2017.[12]

On June 15, 2020, SuperKEKB set a new world record for the highest instantaneous luminosity for a colliding-beam accelerator: 2.22×1034 cm−2s−1. The previous world record of 2.14×1034 cm−2s−1 was achieved by LHC in 2018.[13][14] Since then, SuperKEKB has improved its own record, reaching 5.1×1034 cm−2s−1 in December 2024.[15]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Ohnishi, Yukiyoshi; Abe, Tetsuo; Adachi, Toshikazu; Akai, Kazunori; Arimoto, Yasushi; Ebihara, Kiyokazu; Egawa, Kazumi; Flanagan, John et al. (2013-01-01). "Accelerator design at SuperKEKB". Progress of Theoretical and Experimental Physics 2013 (3): 3A011. doi:10.1093/ptep/pts083. Bibcode: 2013PTEP.2013cA011O. 
  2. ↑ "KEK｜High Energy Accelerator Research Organization" (in en-US). https://www.kek.jp/en/. 
  3. ↑ 3.0 3.1 3.2 "SuperKEKB". http://www-superkekb.kek.jp/. 
  4. ↑ "Congratulations to SuperKEKB for "first turns" | CERN" (in en). https://home.cern/about/updates/2016/03/congratulations-superkekb-first-turns. 
  5. ↑ "Electrons and Positrons Collide for the first time in the SuperKEKB Accelerator" (in en). https://www.kek.jp/en/newsroom/2018/04/26/0700/. 
  6. ↑ "SuperKEKB collider achieves the world's highest luminosity" (in en). 2020-06-28. https://www.bnl.gov/newsroom/news.php?a=117285. 
  7. ↑ Patrignani, C.; Group, Particle Data (2016). "Review of Particle Physics" (in en). Chinese Physics C 40 (10). doi:10.1088/1674-1137/40/10/100001. ISSN 1674-1137. Bibcode: 2016ChPhC..40j0001P. http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22. 
  8. ↑ "Belle II Experiment" (in en-US). http://belle2.jp. 
  9. ↑ "SuperKEKB". https://www-superkekb.kek.jp/. 
  10. ↑ SuperB Collaboration (2007-09-04). "SuperB: A High-Luminosity Asymmetric e+ e- Super Flavor Factory. Conceptual Design Report". arXiv:0709.0451 [hep-ex].
  11. ↑ "Italy cancels €1bn SuperB collider - physicsworld.com" (in en-GB). http://physicsworld.com/cws/article/news/2012/nov/28/italy-cancels-euro-1bn-superb-collider. 
  12. ↑ "Belle II Experiment on Twitter" (in en). Twitter. https://twitter.com/belle2collab/status/830967556034867200. 
  13. ↑ "KEK reclaims luminosity record" (in en-GB). 2020-06-30. https://cerncourier.com/a/kek-reclaims-luminosity-record/. 
  14. ↑ "SuperKEKB collider achieves the world's highest luminosity" (in en). 26 June 2020. https://www.interactions.org/press-release/superkekb-collider-achieves-worlds-highest-luminosity. 
  15. ↑ "SuperKEKB/Belle II Complete 2024 Operations". 2025-01-10. https://www2.kek.jp/ipns/en/news/7015/. 



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