third andean school on nuclear physics

Third Andean School on Nuclear Physics

Roelof Bijker 3rd Andean School on NP 1

2

Quarks, Partons and Color• Introduction• 1. Quarks • Quark model• Baryons and mesons• 2. Partons • Deep Inelastic Scattering• Structure functions• 3. Color• Strong Interaction: QCD• Exotics: tetraquarks & pentaquarks

Roelof [email protected]

2Roelof Bijker 3rd Andean School on NP

Spin-Statistics: Color

Three identical quarks with aligned spins!

Extra degree of freedom: color q, q, q

Greenberg, Han & Nambu

Hadrons are color singlets:


Hadron Production

Consistent with Nc=3 colors!


Hadron Production


Pion Decay

Consistent with Nc=3 colors!


SU(3) Color

Gell-Mann matrices: a

Fundamental Symmetry of the Strong Interaction


Gauge Symmetries

Covariant derivative

Gluon gauge fields

Global gauge invariance


Local gauge invariance

QCD LagrangianFree gluon Lagrangian (gauge invariant)

QCD Lagrangian


QED vs QCD

QED is an abelian gauge theory with U(1) symmetry

QCD is a non-abelian gauge theory with SU(3) symmetry

Both are relativistic quantum field theories that can be described by Lagrangians:

uv

uv

u

u

u

u FFAemiL4

1)(

uv

a

a

uv

a

ujka

u

jkjku

u

jk GGGqTqgqmiqL4

1)()(

QED:

m=electron mass

=electron spinor electron-photon

interaction

Au=photon field (1)

Fuv=uAv-vAu

m=quark mass

j=color (1,2,3)

k=quark type (1-6)

q=quark spinor

quark-gluon

interaction Gau=gluon field (a=1-8)

Gauv=u G

av -v G

au-gfabcG

bu G

cv

QCD:

Ta’s (a=1-8) are the generators of SU(3).

Ta’s are 3x3 traceless hermitian matrices. [Ta, Tb]=ifabcTc

fabcstructure constants

gluon-gluon

interaction

(3g and 4g)


Screening and Anti-Screening

QED: quantum fluctuations polarize vacuum and screen electron charge at large distances

QCD: quark vacuum fluctuations screening (as in QED)

QCD: gluon quantum fluctuations anti-screening (not present in QED)

Gluons dominate net result is anti-screening


G. Ingelman: QCD

QED: Quantum fluctuations polarise vacuum and screen electron charge at large dist.

QCD: Quark vacuum fluctuation screening (as in QED)

QCD: Gluon vacuum fluctuation anti-screening (not in QED)

opposite field direction

weakens field

same field direction

strengthens field


Running Coupling Constant

Increases with energy

Decreases with distance

Decreases with energy

Increases with distance


Asymptotic Freedom


Infrared slavery

Asymptotic freedom

Gross, Wilczek and Politzer, 1973

QCD Corrections

11/3


OZI Rule


OZI allowed OZI suppressedSoft gluons Hard gluons

Okubo, Zweig, Iizuka rule: Strong interaction processes where the final states can only be reached through quark-antiquark annihilation are suppressed

QCD: inital and final states are only connected by gluons

Charmonium and Bottomionium


Color Confinement and Exotics


Hadrons are color singlet (or color neutral) combinations of quarks, antiquarks and gluons

k=1, l=0, m=0 : baryonsk=0, l=1, m=0 : mesonsk=0, l=0, m=1 : anti-baryons

Exoticsk=0, l=2, m=0 : tetraquarks

Fernando Navarra (Monday)k=1, l=1, m=0 : pentaquarks

Glueballs: 3g, 4gLHCb 2015: Discovery of Pentaquark

3rd Andean School on NP 20Roelof Bijker

LHCb: Pentaquark• PRL 115, 072001, PRL 117, 082002, PRL 117, 082003

• Pc(4380) and Pc(4450)

• Favored spin assignment JP=3/2- and 5/2+

• JLab proposal arXiv:1609.00676



Molecular state Pentaquark state

Classification

Hidden charm pentaquark stateswith spin in the quark model.

Flavor decuplet Flavor octet


Standard Model


QCD: strong interaction

QED: em interactionweak interaction

Gauge structure: SU(3) x SU(2) x U(1)

Summary and Conclusions

• Hadrons composed of quarks, antiquarks and gluons

• QCD is the fundamental theory of the stronginteraction between quark and gluons

• SU(3) color symmetry

• Quarks are spin ½ particles

• Gluons are massless spin 1 gauge bosons

• Running coupling constant, asymptotic freedom

• Physical particles are color singlets: baryons, mesons, antibaryons, tetraquarks, pentaquarks, glueballs, …


Bibliography• Textbooks:• Close – Introduction to Quarks and Partons (1979)• Halzen and Martin – Quarks and Leptons (1984)• Griffiths – Introduction to Elementary Particles (1987)• Perkins – Introduction to High Energy Physics (4th edition,

2000)• Thomas and Weise – The Structure of the Nucleon (2000)• Particle Data Group (http://pdg.lbl.gov)

• Lecture Notes:• Ingelman – QCD• Kass – QCD• Grinstein – Introductory lectures on QCD• Skands – Introduction to QCD


Particle History• Close – The Cosmic Onion (1983)

• Pickering – Constructing Quarks (1984)

• Crease and Mann – The Second Creation (1986)

• Riordan – The Hunting of the Quark (1987)

• Lederman and Teresi – The God Particle (1993)

• Veltman – Facts and Mysteries in Elementary Particle Physics (2003)

• Lederman and Hill – Symmetry and the Beautiful Universe (2004)

• Baggott – The Quantum Story (2011)


Third Andean School on Nuclear Physics


Neelima, Carolina, Fernando & Diego Thank you very much!

third andean school on nuclear physics

Documents