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1
Quark and Lepton
Kihyeon Cho
March 22, 2011HEP
ContentsContents
Introduction Fermion-BosonHistory
Particle and Antiparticle입자물리학과 노벨상
Quark and LeptonInteractionsConservationNatural Units
2
Quark and LeptonQuark and Lepton
3
10
Quark Model Quark Model
d u
0zIs
2
1zI2
1zI
S=0
S=-1
)(quarkQ
(Triplet)
d u
0zIs
2
1zI
2
1zI
S=0
S=1
)( quarkAntiQ
(Anti- Triplet)
Perkins 5.1
Quark ModelQuark Model
)(ddd )(0 udd )(uuu)(uud
)(* uss
)(* dss
)(* dds
)(* uus
)(0* uds
)(sss
Perkins 5.1
13
Perkins 5.1
Spin 1/2 Spin 3/2
Quark ModelQuark Model
When Gell-Mann proposed the quark model, was not yet observed.
2
2
2
/1533)2(
/1385)1(
/1232)0(
*
*
cMevSM
cMevSM
cMevSM
??)3( SM
Perkins 5.2
Quark ModelQuark Model
2/150)2()3( * cMevSMSM
We can guess its mass by observing the mass gap between two adjacent strangeness.
2- 1683MeV/cabout was of mass estimated The
Perkins 5.2
Baryon DecupletBaryon DecupletBaryon Decuplet (J=3/2)
Expect 10 states.
Prediction of the (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 ModelQuark 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.
) 0()()2
3( orbitalsymmetricLuuuS z
Perkins 5.2
Quark ModelQuark Model
The postulate
1.Quarks carry three different “color charges”.
2.Only color-neutral objects can be observed in nature.
Suppose three colors are r, y, and g.
0 gyr
0 rr
0 yy
0 gg
means anticolor.gyr ,,
Quark ModelQuark Model
) 0()()2
3( orbitalsymmetricLuuuS gyrz
All other combinations would fail to cancel the color charges each other
The problem of Pauli’s exclusion principle is also naturally solved
Quark ModelQuark 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
),,,,,( tbcsdu),,,,,( vvve e
21
Summary of Quark ModelSummary of Quark Model
Summary of LeptonSummary of Lepton
23Ref. 최성렬교수
(2008)
SummarySummary
24
SummarySummary
25
ReferencesReferences
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)
Thank you.Thank you.