Structure and spin of the nucleon

1
Structure and spin of the nucleon
Harut Avakian(JLab)

• focus on increasing theoretical and experimental
  support for the nucleon and nuclear 3D PDF
  programs worldwide
• model-independent procedure for the flavor
  decomposition

2
Gluon polarization
With upper limit may saturate the sum rule
No need for orbital momentum?
3
Drell-Yan
a test of QCD
SeaQuest Spectrometer
Low Drell-Yan cross section requires a high
intensity beams
Nuclotron based Ion Collider fAcility

• Clean probe to study hadron structure
• convolution of parton distributions
• no QCD final state effects
• no fragmentation process

4
Drell-Yan projections
4ltMlt9 GeV/c2
Drell-Yan beam results are in agreement with the
simulations
Boer-Mulders
Sivers
E-1027 Collaboration
3.2 x 1018 total protons (2 years)
Pb 70
Precision measurements of DY asymmetries
precision TMDs?
5
SIDIS at JLab12
p
E. Cisbani
6
AUT studies using SOLID
E12-11-108
Precision 4-d mapping of target SSA using SoLID
and polarized NH3(p) target
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(No Transcript)
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Sivers effect p from EIC
vs 140 GeV, vs 50 GeV and vs 15 GeV EIC
configurations, respectively. Event counts
correspond to an integrated luminosity of 30 fb-1
arXiv1108.1713

• Large acceptance and energy range of EIC makes it
  ideal place to study the contributions of sea
  quarks to Sivers asymmetry

9
Extracting Sivers function from asymmetries
EIC with energy setting of vs 45 GeV and an
integrated lumi of 4 fb-1
Extraction based on Gaussian Sivers, generated
and then extracted with assumption of the same
shape as used in generation (unclear systematics)

• Invisible error bars are due to specific
  procedure and may be misleading.
• Need realistic error bars, need decomposition
  procedure

10
flavor and spin effects on kT
gt
B.Musch et al arXiv1011.1213
g1qDq(q-q-)/2
P. Schweitzer et al arXiv1210.1267
Higher probability to find a quark anti-aligned
with proton spin, also more sea and d-quarks at
large kT

• kT-distributions of TMDs depend on flavor and
  spin
• In medium fractions of spin and orbital momentum
  change (nuclear targets)

10
11
flavor and spin effects on bT
B.Pasquini et al
G. Miller et al Phys.Rev.C84045205,2011

• space distributions depend on flavor and spin
  (medium?)

12
Higher twists
Higher twists large and underlying
interactions/correlations require more attention!
13
Summary

• focus on increasing theoretical and experimental
  support for the nucleon and nuclear 3D PDF
  programs worldwide
• model-independent procedure for the flavor
  decomposition of 3D PDFs

HAVE A VERY PRODUCTIVE WEEK!
14

• Support slides

15
From low PT TMDs to high PT collinear
Matching the angular integrated cross section at
low PT to fixed order pQCD collinear
factorization calculations at high PT
Transverse momentum dependent QgtgtPTgtLQCD
Collinear Q,PTgtgtLQCD
LQCDltlt PT ltltQ
PT
Georgi Politzer
Collinear/ Twist-2
Twist-3 Cahn
Leading Twist
PT

Efremov, Teryaev Qiu, Sterman
Higher Twist
Collinear/ twist-3
Twist-2 Sivers
PT
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Correlations of spin, longitudinal and transverse
degrees

• What are the kT distributions of partons?
• Do they depend on spin and flavor of partons?
• Do they modify in medium, and how ?
• How studies of proton transverse structure will
  improve our understanding of medium effects?
• How studies of medium modifications will improve
  our understanding of the proton structure?

• Possible new tools
• Polarized DIS resolve the spin effects in medium
• Polarized and unpolarized SIDIS resolve flavor
  and spin effects

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Kinematic correlations at finite Q2
From energy/momentum conservation
arXiv 1106.6177
energy of the parton have to be less than the
energy of the parent hadron
x and kT are not independent at low Q2 even in
factorized Gaussian approach!
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Medium modified spin observables (NJL model)
I. Cloet
EMC effect essentially a consequence of binding
at the quark level
19
Transverse densities in the nucleon in nuclear
matter
Quark transverse charge densities inside an
unpolarized proton arXiv1304.5926 (Yakhshiev
Kim )
Skyrme model
proton
medium

• form factors of the nucleon fell off faster in
  nuclear matter
• the size of the nucleon tends to bulge out in
  nuclear matter.

20
The Multi-Hall SIDIS Program at 12 GeV
M. Aghasyan, K. Allada, H. Avakian, F.
Benmokhtar, E. Cisbani, J-P. Chen, M.
Contalbrigo, D. Dutta, R. Ent, D.
Gaskell, H. Gao, K. Griffioen, K. Hafidi, J.
Huang, X. Jiang, K. Joo, N.
Kalantarians, Z-E. Meziani, M. Mirazita, H.
Mkrtchyan, L.L. Pappalardo, A. Prokudin,
A. Puckett, P. Rossi, X. Qian, Y. Qiang, B.
Wojtsekhowski
for the Jlab SIDIS working group

• The complete mapping of the multi-dimensional
  SIDIS phase space will allow a comprehensive
  study of the TMDs and the transition to the
  perturbative regime.
• Flavor separation will be possible by the use of
  different target nucleons and the detection of
  final state hadrons.
• Measurements with pions and kaons in the final
  state will also provide important information on
  the hadronization mechanism in general and on the
  role of spin-orbit correlations in the
  fragmentation in particular.
• Higher-twist effects will be present in both TMDs
  and fragmentation processes due to the still
  relatively low Q2 range accessible at JLab, and
  can apart from contributing to leading-twist
  observables also lead to observable asymmetries
  vanishing at leading twist. These are worth
  studying in themselves and provide important
  information on quark-gluon correlations.

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Sivers TMD evolution
Drell-Yan
SIDIS
Aybat, Prokudin Rogers
C12-11-111
TMD Evolution may explain existing differences
between HERMES and COMPASS . Aybat, Prokudin
Rogers arXiv1112.4423
Comparison of JLab12 data with HERMES and COMPASS
will pin down the Q2 evolution of Sivers
asymmetry.