HEP Quark and Lepton Kihyeon Cho
S=0 S=1 S=-1 S=0 (Triplet) (Anti- Triplet) Quark Model Perkins 5.1
Quark Model Perkins 5.1
Perkins 5.1 Spin 3/2 Spin 1/2
When Gell-Mann proposed the quark model, was not yet observed. Quark Model Perkins 5.2
Perkins 5.2 Quark Model We can guess its mass by observing the mass gap between two adjacent strangeness.
Perkins 5.2 Baryon Decuplet Baryon Decuplet (J=3/2) Expect 10 states. Prediction of the W- (mass =1672 MeV/c2, S=-3) Use bubble chamber to find the event. 1969 Nobel Prize to Gell-Mann! “Observation of a hyperon with strangeness minus 3” PRL V12, 1964.
Perkins 5.2 Quark Model There were a couple of problems in accepting Gell-Mann’s quark model. First, other combinations of quarks such as two quarks were not observed and there is no evidence for the existence of quark. Second, problem of Pauli’s exclusion principle.
Quark Model • The postulate • Quarks carry three different “color charges”. • Only color-neutral objects can be observed in nature. Suppose three colors are r, y, and g. means anticolor.
Quark Model All other combinations would fail to cancel the color charges each other The problem of Pauli’s exclusion principle is also naturally solved
Quark Model So, why can only color-neutral objects be observed in nature? Maybe the answer will be provided by QCD(quantum chromodynamics) Nowadays, people have established the standard model of elementary particle physics assuming the six quarks and the six leptons
Summary Ref. 최성렬교수(2008)
References • Class P720.02 by Richard Kass (2003) • B.G Cheon’s Summer School (2002) • S.H Yang’s Colloquium (2001) • Class by Jungil Lee (2004) • PDG home page (http://pdg.lbl.gov)