Upsilon meson

Υ (1S)

The Υ meson is an uncharged meson. It is denoted by the Greek capital letter Υ. As a symbol of this Ypsilon used with a " ram's horns " is always: .

It is a bound state of a bottom quark and a bottom antiquark, ie a bottomonium. Like all quarkonium mesons are all its flavor quantum numbers zero.

The Υ was discovered in 1977 at Fermilab by the E288 group under Leon Lederman. It was the first discovered particle containing 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/c2. Most commonly it decays into three gluons, which then hadronisieren, or via a virtual photon into quark-antiquark or lepton pairs ( τ τ -, μ μ - and e e-).

Important is the Υ -meson in B- factories. There is exploited that a certain excitation of this particle, which, almost decays Υ ( 4S) only in two B- mesons. This can therefore be reliably produce and investigate. The lighter Υ - meson ( Υ (1S), Υ ( 2S), Υ (3S) ) do not have enough mass to decay into B- mesons.