Belle II experiment

Coordinates: 36°9′28″N 140°4′30″E / 36.15778°N 140.07500°E / 36.15778; 140.07500

The Belle II experiment is a particle physics experiment designed to study the properties of B mesons (heavy particles containing a bottom quark). Belle II is the successor to the Belle experiment, and commissioned at the SuperKEKB[1] accelerator complex at KEK in Tsukuba, Ibaraki prefecture, Japan. The Belle II detector was "rolled in" (moved into the collision point of SuperKEKB) on April 2017.[2][3] Belle II started taking data in early 2018.[1] Over its running period, Belle II is expected to collect around 50 times more data than its predecessor mostly due to a 40-fold increase in an instantaneous luminosity provided by SuperKEKB as compared to the previous KEKB accelerator.[1]

The opened Belle II detector before installation of the inner tracking detectors.

Detector upgradeEdit

Much of the original Belle detector has been upgraded[4] to cope with the higher instantaneous luminosity provided by the SuperKEKB accelerator.[1] Close to the beam pipe, the two innermost layers of Belle's silicon vertex detector have been replaced by a depleted field effect transistor (DEPFET) pixel detector, and a larger silicon vertex detector.[4][5] A larger central tracking system, a wire drift chamber, has been installed.[4] Two new particle identification systems have been installed in the forward endcap (consisting of an aerogel ring-imaging Cherenkov detector)[4][6] and in the barrel (consisting of quartz bars utilising totally internally reflected Cherenkov photons and measuring the time of propagation).[4][7] The original CsI(Tl) electromagnetic calorimeter has been re-used (a new pure CsI calorimeter is being designed for the forward endcap[8] to be installed at a later stage[8][9]). The calorimeter readout electronics have been upgraded.[4] Finally, scintillators have been installed in the endcaps and inner layers of Belle's
and muon detector, the original resistive plate chambers from Belle are reused in the outer layers of the barrel.[4][10]

The target dataset is 50 ab−1 at Belle II[4] compared to 988 fb−1 (with 711 fb−1 at the Υ(4S) energy) at Belle.[11]

Construction work on the Central Drift Chamber (CDC) of the Belle II experiment.


The Belle II data taking is separated into three phases:[12]

  • Phase I — completed Feb–June 2016: SuperKEKB commissioning to characterize the beam environment
  • Phase II — started early 2018, running without the inner silicon-based VXD tracking system to characterize background radiation in the innermost tracking system
  • Phase III — started 2019: data taking with the complete Belle II detector

On November 22 2018 the Belle II detector was completed with the installation of the VerteX Detector (VXD).[13] On March 25th 2019 the first collisions of the actual physics program were detected.[14]

See alsoEdit


  1. ^ a b c d "SuperKEKB". Retrieved 2017-04-28.
  2. ^ "Belle II Experiment on Twitter". Twitter. Retrieved 2017-05-07.
  3. ^ "Belle II rolls in - CERN Courier". Retrieved 2017-05-22.
  4. ^ a b c d e f g h Abe, T.; et al. (October 2010). "Belle II Technical Design Report". arXiv:1011.0352 [physics.ins-det].
  5. ^ Casarosa, Giulia (2015). "Inner tracking devices at the Belle II experiment". Proceedings, 2015 European Physical Society Conference on High Energy Physics (EPS-HEP 2015) : Vienna, Austria, July 22-29, 2015. p. 255.
  6. ^ Nishida, S.; et al. (2014). "Aerogel RICH for the Belle II forward PID". Nuclear Instruments and Methods in Physics Research Section A. 766: 28–31. Bibcode:2014NIMPA.766...28N. doi:10.1016/j.nima.2014.06.061.
  7. ^ Inami, Kenji (2014). "TOP counter for particle identification at the Belle II experiment". Nuclear Instruments and Methods in Physics Research Section A. 766: 5–8. Bibcode:2014NIMPA.766....5I. doi:10.1016/j.nima.2014.07.006.
  8. ^ a b Manoni, E.; et al. (2017). "The upgrade of the Belle II forward calorimeter". Nuclear Instruments and Methods in Physics Research Section A. 845: 524–527. Bibcode:2017NIMPA.845..524M. doi:10.1016/j.nima.2016.06.074.
  9. ^ "Electromagnetic Calorimeter | Belle II Experiment". Retrieved 2017-05-07.
  10. ^ Aushev, T.; et al. (2015). "A scintillator based endcap KL and muon detector for the Belle II experiment". Nuclear Instruments and Methods in Physics Research Section A. 789: 134–142. arXiv:1406.3267. Bibcode:2015NIMPA.789..134A. doi:10.1016/j.nima.2015.03.060. S2CID 118613296.
  11. ^ Bevan, A. J.; Golob, B.; Mannel, Th; Prell, S.; Yabsley, B. D.; Aihara, H.; Anulli, F.; Arnaud, N.; Aushev, T. (2014-11-01). "The Physics of the B Factories". The European Physical Journal C. 74 (11): 3026. arXiv:1406.6311. Bibcode:2014EPJC...74.3026B. doi:10.1140/epjc/s10052-014-3026-9. ISSN 1434-6044. S2CID 9063079.
  12. ^ N.Braun - Hadron Spectroscopy Studies at Belle II
  13. ^ @belle2collab (22 November 2018). "VerteX Detector (VXD) successfully installed in #Belle2. The Belle II detector is now complete!" (Tweet) – via Twitter.
  14. ^ Kick-off of the Belle II Phase 3 Physics Run

External linksEdit