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the SuperKEKB accelerator.[1] Close to the beam pipe, the two innermost layers of Belle's silicon vertex detector have been replaced by a depleted field effect transistor (DEPFET) pixel detector, and a larger silicon vertex detector.[4][5] A larger central tracking system, a wire drift chamber,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
K0
L
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.

TimelineEdit

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

ReferencesEdit

  1. ^ a b c d "SuperKEKB". www-superkekb.kek.jp. Retrieved 2017-04-28.
  2. ^ "Belle II Experiment on Twitter". Twitter. Retrieved 2017-05-07.
  3. ^ "Belle II rolls in - CERN Courier". cerncourier.com. 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". belle2.jp. 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