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Quark and Lepton

Kihyeon Cho

March 22, 2011HEP

ContentsContents

Introduction Fermion-BosonHistory

Particle and Antiparticle입자물리학과 노벨상

Quark and LeptonInteractionsConservationNatural Units

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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

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Summary of Quark ModelSummary of Quark Model

Summary of LeptonSummary of Lepton

23Ref. 최성렬교수

(2008)

SummarySummary

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SummarySummary

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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.