Υ meson
|
Υ (1S) |
|
|---|---|
| classification | |
|
Boson meson hadron |
|
| properties | |
| electric charge | neutral |
| Resting energy | 9460.30 (26) MeV |
| Spin parity | 1 - |
| Isospin | 0 (z component 0) |
| average lifespan | 1.218 (28) · 10 −20 s |
| Decay width | 0.05402 (125) MeV |
| Interactions |
strong weak electromagnetic gravitation |
|
Quark composition |
1 bottom and 1 anti-bottom |
The Υ meson is an uncharged meson . It is denoted by the Greek capital letter Υ . As a symbol of a Ypsilon is here with "always ram horns" uses: .
It is a bound state of a bottom quark and a bottom anti quark , i.e. a bottomomonium . As with all Quarkonium mesons are all his flavor - quantum numbers zero.
The Υ was discovered in 1977 at Fermilab by the E288 group under Leon Max Lederman . It was the first particle that was discovered to contain a b-quark. The lifetime of the ground state, called Υ (1S), is 1.21 · 10 −20 seconds and it has a mass of about 9.46 GeV / c 2 . Most often it decays into three gluons , which then hadronize , or via a virtual photon into quark- antiquark or lepton pairs (τ + τ - , μ + μ - and e + e - ).
The Υ meson is important in B factories . There it is exploited that a certain excitation of this particle, the Υ (4S), almost exclusively decays into two B mesons . These can therefore be reliably produced and examined. The lighter Υ mesons (Υ (1S), Υ (2S), Υ (3S)) do not have enough mass to decay into B mesons.
literature
- DC Hom et al .: Observation of a Dimuon Resonance at 9.5 GeV in 400 GeV Proton-Nucleus Collisions . "In: Phys. Rev. Lett. 39. 1977, 252-255. (PDF; 348 KB)
- John Yoh: The Discovery of the b Quark at Fermilab in 1977: The Experiment Coordinator's Story . In: AIP Conf. Proc. 424. 1998, 29-42. (PDF; 196 KB)
- Properties (Particle Data Group) (PDF; 84 KB)
- D. Besson et al .: Measurement of the direct photon momentum spectrum in Υ (1S), Υ (2S), and Υ (3S) decays . in phys. Rev. D74, 2006, 012003
See also
Individual evidence
- ↑ The information on the particle properties (info box) are, unless otherwise stated, taken from: J. Beringer et al. ( Particle Data Group ): 2013 Review of Particle Physics. In: Physical Review D . Vol. 86, 2012, 010001 and 2013 partial update for the 2014 edition. Particle Data Group, accessed May 22, 2018 .