Accessing Orbital Angular Momentum Thru Pion Cloud

Itaru Nakagawa

RIKEN/RBRC

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

S + L = J

€

p

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

−1

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟

€

S + L = J

€

p

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

−1

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 +1( ) =

€

S + L = J

€

p

€

Nπ

P-wave

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

−1

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 +1( ) = +

1

2

€

S + L = J

€

p

€

Nπ

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

−1

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 +1( ) = +

1

2

€

3

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟

€

S + L = J

€

p

€

Nπ

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

−1

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 +1( ) = +

1

2

€

3

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 −1( ) =

€

S + L = J

€

p

€

Nπ

€

Δπ

Proton Spin +1/2

€

+1

2+ 0 = +

1

2

€

−1

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 +1( ) = +

1

2

€

3

2+ 0

⎛

⎝ ⎜

⎞

⎠ ⎟+ 0 −1( ) = +

1

2

€

S + L = J

€

p

€

Nπ

€

Δπ

P-waveP-wave

Nucleon EM Form Factors

Nucleon EM Form Factors low Q

Nucleon EM Form Factors

phenomenological fit :

“smooth” part

(sum of 2 dipoles)

+ “bump”

(gaussian)

6 parameter fit for each FF

pronounced structure in all FF around Q 0.5 GeV/c pion cloudpion cloud

J.Friedrich & Th. Walcher, EPJA A17, 607 (2003)

Sea Asymmetry from Drell-Yan Processes

Towell et al., Phys.Rev. D64 (2001) 052002

Profounding Example of Pion Cloud

excess

Extra dbar in proton g.s.

Sea Quarks Carry Major Orbital Angular Momentum Component?

€

d

Pion Model Prediction of Orbital Angular Momentum

A.W. Thomas

JLab

Tony Thomas (3)

Tony Thomas (1)

Proton Spin +1/2

€

Z

€

Nπ

€

Δπ

70% 20~25% 5~10%

Tony Thomas (2)

Tony Thomas (4)

Tony Thomas

Tony Thomas(6)

Experiment Sensitive to p-Wave π

€

γ*p→ Δ → π 0p

Angular Distribution

Pion Cloud Model

Atomic Electron Scattering

Virtual pion pickup

Probing Pion Cloud

Need : Q2 ~ 0.2 GeV/c2 Compass

Calculation by T. Horn

+

Summary

• pion cloud is one of the way to access Orbital Angular Momentum

• There are (will be) many experiments which explore pion cloud

• Not good idea yet to be done at J-PARC

Elastic Scattering

Cross Sections

Valence Quark Interchange

Concerns

• So far, q-interchange model is only quantitative level Qualitatively, regge pole)

• Elastic Soft Mechanism

• Elastic No Fragmentation?

• Sensitivity to sea? p

Relativistic Valence Quark

rXiv:0709.4067 ﾊ [hep-ph]