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Current status of spin-dependent parton distributions Nobuo Sato
ODU/JLab
27th Workshop on Deep-Inelastic Scattering and Related Subjects DIS 2019 Turin, Italy
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Current status of spin-dependent parton distributions Nobuo Sato - - PowerPoint PPT Presentation
Current status of spin-dependent parton distributions Nobuo Sato - - PowerPoint PPT Presentation
Current status of spin-dependent parton distributions Nobuo Sato ODU/JLab 27th Workshop on Deep-Inelastic Scattering and Related Subjects DIS 2019 Turin, Italy 1 / 17 2 / 17 2 / 17 Proton has spin 1/2 because its a fermion. Why need
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“Proton has spin 1/2 because it’s a fermion. Why need more explanation? ” Hatta
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“Proton has spin 1/2 because it’s a fermion. Why need more explanation? ” Hatta “Spin crisis in the late 80’s”
- Quark model of nucleon → 3 massive quarks
- Nucleon is in the ground state (s-state) → no OAM
- Quarks expected to carry most of the nucleon’s spin
1 2 = 1 2∆Σ
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3 / 17
“Proton has spin 1/2 because it’s a fermion. Why need more explanation? ” Hatta “Spin crisis in the late 80’s”
- Quark model of nucleon → 3 massive quarks
- Nucleon is in the ground state (s-state) → no OAM
- Quarks expected to carry most of the nucleon’s spin
1 2 = 1 2∆Σ
But ∆Σ ≃ 0.28(4) JAM15
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3 / 17
“Proton has spin 1/2 because it’s a fermion. Why need more explanation? ” Hatta “Spin crisis in the late 80’s”
- Quark model of nucleon → 3 massive quarks
- Nucleon is in the ground state (s-state) → no OAM
- Quarks expected to carry most of the nucleon’s spin
Ok ... QCD is more complicated: “Spin crisis challenge”
1 2 = 1 2∆Σ
But ∆Σ ≃ 0.28(4) JAM15
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In terms of total angular momentum (GPDs):
1 2 = Jq + Jg
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In terms of total angular momentum (GPDs):
1 2 = Jq + Jg
In terms of spin (PDFs) and OAM:
1 2 = 1 2∆Σ + Lq + ∆g + Lg
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4 / 17
In terms of total angular momentum (GPDs):
1 2 = Jq + Jg
In terms of spin (PDFs) and OAM:
1 2 = 1 2∆Σ + Lq + ∆g + Lg
Moments of helicity distributions
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A big community working on the challenge
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Small x asymptotics using large Nc
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Small x asymptotics using large Nc
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Small x asymptotics using large Nc
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Kovchegov, Sievert, Pitonyak (’17)
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OAM as a next-to-eikonal effect
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OAM as a next-to-eikonal effect
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OAM as a next-to-eikonal effect
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Hatta, Nakagawa, Xiao, Yuan, Zhao (’17)
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Lattice QCD
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1 2 = Jq + Jg
Striped segments: → connected contributions Solid segments: → disconnected contributions Alexandrou et al.,(ETMC) (’17)
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Lattice QCD: quasi-PDF
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Lattice QCD: quasi-PDF
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ETMC
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Lattice QCD: quasi-PDF
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ETMC
∆ ¯ d < ∆¯ u ∆ ¯ d > ∆¯ u
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10 / 17
Global analyses
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Valence polarization
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JAM15 MC sampling approach All ∆DIS data with W 2 > 4GeV2 Constraints on twist-3 distributions No sign of ∆d(x)/d(x) → 1
NS, Melnitchouk, Kuhn, Ethier, Accardi (’15)
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Gluon polarization
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p↑ + p↑(↓) → j + X
De Florian, Sassot, Stratmann, Vogelsang (’14)
Single fit method + Lagrange
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Gluon polarization
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p↑ + p↑(↓) → j + X
De Florian, Sassot, Stratmann, Vogelsang (’14) 1
0.001
dx∆g(x) = 0.013 + 0.702 − 0.314 Single fit method + Lagrange
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Light sea polarization
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p↑ + p → W ± → e± + ν + X
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Light sea polarization
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p↑ + p → W ± → e± + ν + X
Nocera (’17)
NNPDF Reweighting
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Light sea polarization
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Light sea polarization
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Xu (spin 18)
∆¯ u > ∆ ¯ d
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Strange polarization
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Most of existing analysis on ∆PDFs used additional constraints Neutron decay →
1
0 dx (∆u+ − ∆d+) = gA
Hyperon decay →
1
0 dx (∆u+ + ∆d+ − 2∆s+) = g8
∆s+ puzzle g8? ∆SIDIS (¯ s → K FF)? fiction?
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Strange polarization
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Ethier, NS, Melnitchouk (’17)
Current ∆SIDIS unable to discriminate strange polarization No conflict between the ∆DIS and ∆SIDIS A combined (∆)PDF & FF is needed
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Summary and outlook
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