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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]