The Belle experiment was a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers, at the High Energy Accelerator Research Organisation (KEK) in Tsukuba, Ibaraki Prefecture, Japan. The experiment ran from 1999 to 2010.
The Belle detector was located at the collision point of the asymmetric-energy electron-positron collider, KEKB. Belle at KEKB together with the BaBar experiment at the PEP-II accelerator at SLAC were known as the B-factories as they collided electrons with positrons at the center-of-momentum energy equal to the mass of the
(4S) resonance which decays to pairs of B mesons.
The Belle detector was a hermetic multilayer particle detector with large solid angle coverage, vertex location with precision on the order of tens of micrometres (provided by a silicon vertex detector), good distinction between pions and kaons in the momenta range from 100 MeV/c to few GeV/c (provided by a Cherenkov detector), and a few-percent precision electromagnetic calorimeter (made of CsI(Tl) scintillating crystals).
The Belle II experiment is an upgrade of Belle that was approved in June 2010. It is currently being commissioned, and is anticipated to start operation in 2018. Belle II is located at SuperKEKB (an upgraded KEKB accelerator) which is intended to provide a factor 40 larger integrated luminosity.
The experiment was motivated by the search for CP-violation. However the experiment also performed extensive studies of rare decays, searches for exotic particles and precision measurements of the properties of D mesons, and tau particles. The experiment has resulted in almost 300 publications in physics journals.
Highlights of the Belle experiment include
- an observation of large CP-violation in the neutral B meson system
- measurement of the branching fraction of inclusive decays
- observation of the transition with  and 
- measurement of using the Dalitz plot
- measurement of the CKM quark mixing matrix elements and 
- observation of direct CP-violation in  and 
- observation of transitions
- evidence for 
- observations of a number of new particles including the X(3872)
The KEKB accelerator was the world's highest luminosity machine at the time. A large fraction of the data was collected at the
(4S). The instantaneous luminosity exceeded ×1034 cm−2·s−1. The 2.11integrated luminosity collected at the
(4S) mass was about fb−1 (corresponding to 771 million 710
meson pairs). About 10% of the data was recorded below the
(4S) resonance in order to study backgrounds. In addition, KEKB carried out special runs at the
(5S) resonance to study
s mesons as well as on the
(3S) resonances to search for evidence of Dark Matter and the Higgs Boson. The samples of
(5S) collected by Belle are the world largest samples available.
- 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. Bibcode:2014EPJC...74.3026B. ISSN 1434-6044. doi:10.1140/epjc/s10052-014-3026-9.
- KEK press release
- "Belle II". www.belle2.org. Retrieved 2017-04-28.
- "SuperKEKB". www-superkekb.kek.jp. Retrieved 2017-04-30.
- Abe, T.; Adachi, I.; Adamczyk, K.; Ahn, S.; Aihara, H.; Akai, K.; Aloi, M.; Andricek, L.; Aoki, K. (2010-11-01). "Belle II Technical Design Report". arXiv: [physics.ins-det].
- Cheng, M. T.; Chu, M. L.; Wang, C. H.; Chen, H. S.; Li, J.; Zhu, Y. C.; Wang, T. J.; Yu, Z. Q.; Kawai, H. (1994-01-01). "Letter of intent for a study of CP violation in B meson decays".
- Abe, K.; Abe, K.; Abe, R.; Adachi, I.; Ahn, Byoung Sup; Aihara, H.; Akatsu, M.; Alimonti, G.; Asai, K. (2001-08-14). "Observation of Large CP Violation in the Neutral B Meson System". Physical Review Letters. 87 (9): 091802. Bibcode:2001PhRvL..87i1802A. ISSN 0031-9007. PMID 11531561. doi:10.1103/PhysRevLett.87.091802.
- Abe, K.; Abe, K.; Adachi, I.; Ahn, Byoung Sup; Aihara, H.; Akatsu, M.; Alimonti, G.; Aoki, K.; Asai, K. (2001-07-05). "A measurement of the branching fraction for the inclusive B→Xsγ decays with the Belle detector". Physics Letters B. 511 (2–4): 151–158. Bibcode:2001PhLB..511..151B. doi:10.1016/S0370-2693(01)00626-8.
- Abe, K.; Abe, K.; Abe, R.; Adachi, I.; Ahn, Byoung Sup; Aihara, H.; Akatsu, M.; Asano, Y.; Aso, T. (2001-12-27). "Observation of the Decay B → K l + l −". Physical Review Letters. 88 (2): 021801. Bibcode:2002PhRvL..88b1801A. ISSN 0031-9007. PMID 11801003. doi:10.1103/PhysRevLett.88.021801.
- Ishikawa, A.; Abe, K.; Abe, K.; Abe, T.; Adachi, I.; Ahn, Byoung Sup; Aihara, H.; Akai, K.; Akatsu, M. (2003-12-24). "Observation of B → K * ℓ + ℓ −". Physical Review Letters. 91 (26): 261601. Bibcode:2003PhRvL..91z1601I. ISSN 0031-9007. doi:10.1103/PhysRevLett.91.261601.
- Abe, K.; Abe, K.; Abe, N.; Abe, T.; Adachi, I.; Aihara, H.; Akai, K.; Akatsu, M.; Akemoto, M. (2004-07-06). "Observation of Large C P Violation and Evidence for Direct C P Violation in B 0 → π + π − Decays". Physical Review Letters. 93 (2): 021601. Bibcode:2004PhRvL..93b1601A. ISSN 0031-9007. PMID 15323897. doi:10.1103/PhysRevLett.93.021601.
- Chao, Y.; Chang, P.; Abe, K.; Abe, K.; Abe, N.; Adachi, I.; Aihara, H.; Akai, K.; Akatsu, M. (2004-11-05). "Evidence for Direct C P Violation in B 0 → K + π − Decays". Physical Review Letters. 93 (19): 191802. Bibcode:2004PhRvL..93s1802C. ISSN 0031-9007. PMID 15600826. doi:10.1103/PhysRevLett.93.191802.
- Mohapatra, D.; Nakao, M.; Nishida, S.; Abe, K.; Abe, K.; Adachi, I.; Aihara, H.; Anipko, D.; Arinstein, K. (2006-06-09). "Observation of b → d γ and Determination of | V t d / V t s |". Physical Review Letters. 96 (22): 221601. Bibcode:2006PhRvL..96v1601M. ISSN 0031-9007. PMID 16803300. doi:10.1103/PhysRevLett.96.221601.
- Ikado, K.; Abe, K.; Abe, K.; Adachi, I.; Aihara, H.; Akai, K.; Akemoto, M.; Anipko, D.; Arinstein, K. (2006-12-22). "Evidence of the Purely Leptonic Decay B − → τ − ν ¯ τ". Physical Review Letters. 97 (25): 251802. Bibcode:2006PhRvL..97y1802I. ISSN 0031-9007. PMID 17280341. doi:10.1103/PhysRevLett.97.251802.
- Choi, S.-K.; Olsen, S. L.; Abe, K.; Abe, T.; Adachi, I.; Ahn, Byoung Sup; Aihara, H.; Akai, K.; Akatsu, M. (2003-12-23). "Observation of a Narrow Charmoniumlike State in Exclusive B ± → K ± π + π − J / ψ Decays". Physical Review Letters. 91 (26): 262001. Bibcode:2003PhRvL..91z2001C. ISSN 0031-9007. doi:10.1103/PhysRevLett.91.262001.