Upsilon meson

Upsilon (
ϒ
)

A plot of the invariant mass of muon pairs, from the Upsilon particle discovery paper. The peak at about 9.5 GeV is due to the contribution of the Upsilon meson.
Composition	b b
Statistics	Bosonic
Family	Mesons
Interactions	Strong, weak, Electromagnetic, Gravity
Symbol	ϒ
Antiparticle	Self
Discovered	E288 experiment (1977)
Types	1
Mass	9.46030(26) GeV/c2
Mean lifetime	1.21×10−20 s
Electric charge	0 e
Spin	1
Isospin	0
Hypercharge	0
Parity	-1
C parity	-1

The Upsilon meson (
ϒ
) is a quarkonium state (i.e. flavourless meson) formed from a bottom quark and its antiparticle. It was discovered by the E288 experiment team, headed by Leon Lederman, at Fermilab in 1977, and was the first particle containing a bottom quark to be discovered because it is the lightest that can be produced without additional massive particles. It has a lifetime of 1.21×10⁻²⁰ s and a mass about 9.46 GeV/c² in the ground state.

See also

• Oops-Leon, an erroneously-claimed discovery of a similar particle at a lower mass in 1976.
• The
  ϕ
  particle is the analogous state made from strange quarks.
• The
  J/ψ
  particle is the analogous state made from charm quarks.
• List of mesons

References

• D.C. Hom; et al. (1977). "Observation of a Dimuon Resonance at 9.5 Gev in 400-GeV Proton-Nucleus Collisions" (PDF). Physical Review Letters. 39 (5): 252–255. Bibcode:1977PhRvL..39..252H. doi:10.1103/PhysRevLett.39.252.
• J. Yoh (1998). "The Discovery of the b Quark at Fermilab in 1977: The Experiment Coordinator's Story" (PDF). AIP Conference Proceedings. 424: 29–42. Bibcode:1998AIPC..424...29Y. doi:10.1063/1.55114.
• S. Eidelman et al. (Particle Data Group) (2004). "Review of Particle Physics –
  ϒ
  meson" (PDF). Physics Letters B. 592 (1–4): 1. arXiv:astro-ph/0406663. Bibcode:2004PhLB..592....1P. doi:10.1016/j.physletb.2004.06.001.