The role of orbital angular momentum in the internal spin structure of the nucleon based on collaboration with Y. Nakakoji, H. Tsujimoto 1. Current status of nucleon spin problem 2. Role of CQSM in nucleon structure function physics 3. CQSM analysis of unpolarized GPD 4. Model independent analysis of nucleon spin contents 5. Flavor decomposition of nucleon spin Plan of Talk M. Wakamatsu (Osaka University) : PACSPIN-07
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The role of orbital angular momentum in the internal spin structure of the nucleon based on collaboration with Y. Nakakoji, H. Tsujimoto 1. Current status.
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The role of orbital angular momentum
in the internal spin structure of the nucleon
based on collaboration with Y. Nakakoji, H. Tsujimoto
1. Current status of nucleon spin problem
2. Role of CQSM in nucleon structure function physics
3. CQSM analysis of unpolarized GPD
4. Model independent analysis of nucleon spin contents
5. Flavor decomposition of nucleon spin (model dependent)
6. Summary
Plan of Talk
M. Wakamatsu (Osaka University) : PACSPIN-07
Early stage proposals to explain very small quark spin fraction
(I) Gluon spin hypothesis
(A) naive claim
(B) axial-anomaly of QCD
(II) Quark orbital angular momentum hypothesis
(III) Gluon orbital angular momentum hypothsis
no serious consideration until recently !
OK if The question remains why !
1. Current status of nucleon spin problem
unfavored ? is small, because is large !
but need very large !
Two remarkable recent progresses :
(1) New COMPASS & HERMES analyses
(2) COMPASS, PHENIX, STAR analyses
• Precise measurements of deuteron spin-dependent structure function high statistics, especially at lower x region
• PHENIX : neutral pion double longitudinal spin asymmetry in the p-p collisions• STAR : double longitudinal spin asymmetry in inclusive jet production
in polarized p-p collision
• COMPASS : quasi-real photoproduction of high- hadron pairs
Still totally unknown are and !
Recent interesting observation concerning
“Evidence for the Absence of Gluon Orbital Angular Momentum
in the Nucleon”, S.J. Brodsky and S. Gardner, Phys. Let. B643
The Sivers mechanism for the single-spin asymmetry in the
unpolarized lepton scattering from a transversely polarized nucleon
is driven by the orbital angular momentum of quarks and gluons.
They argued that small single-spin asymmetry on the deuteron
target measured by the COMPASS collaboration is an
indication of small gluon OAM !.
If true, what remains is alone ?
Skyrme model (Ellis-Karliner-Brodsky, 1988)
Chiral Quark Soliton Model (Wakamatsu-Yoshiki, 1991)
Importance of quark orbital angular momentum
Collective quark motion generating rotating M.F. of hedgehog shape
In particular, since the latter is an effective quark theory
- Large chiral soliton picture of the nucleon -
Spin S.R
appearing in high-energy DVCS & DVMP processes
Ji’s angular momentum sum rule
new recent development
through Generalized Parton Distributions (GPDs)
We need more direct empirical information on
possibility of direct measurement of
Factorization
Hard part :
Soft part :
Perturbative QCD
Nonpurturbative QCD
Lattice QCD Effective models of QCD
• most promising in the long run
- still at incomplete stage -
• continuum limit & chiral limit ?
• only lower moments of PDF
• physical interpretation ?
So many !
Necessary condition of good model,
which has predictive power ?
• able to explain many observables
with less parameters !
2. Role of CQSM in nucleon structure function (DIS) physics
Black Box
Advantages of Chiral Quark Soliton Model
parameter-free predictions for PDFs
• a nucleon is a composite of valence quarks and infinitely many
Dirac sea quarks moving in a slowly rotating M.F. of hedgehog shape
• field theoretical nature of the model (proper inclusiuon of polarized
Dirac-sea quarks) enables reasonable estimation of antiquark dist.
Default
Lack of explicit gluon degrees of freedom
• only 1 parameter of the model (dynamical quark mass ) was
already fixed from low energy phenomenology
How to use predictions of this low energy model for parton distributions ?
We follow the spirit of
* M. Glueck, E. Reya, and A. Vogt, Z. Phys. C67 (1995) 433
They start the QCD evolution at the extraordinary low energy scales like
Even at such low energy scales, their PDF fit turns out to need
nonperturbatively generated sea-quarks (and some gluons)
which may be connected with the effects of
meson clouds
Our general strategy
• use predictions of CQSM as initial-scale distributions of DGLAP eq.
for flavor SU(2) CQSM
for flavor SU(3) CQSM
• initial energy scale is fixed to be
pQCD is barely applicable ?
On the Applicability of pQCD ?
NLO
Parameter free predictions of the CQSM : 3 twist-2 PDFs
Transversities [3rd twist-2 PDF]
• Totally different behavior of Dirac-sea contributions in different PDFs !
Isoscalar unpolarized PDF
positivity
sea-like soft component
Isovector unpolarized PDF
Isoscalar longitudinally polarized PDF
New COMPASS data
CQSM
New COMPASS and HERMES fits for in comparison with CQSM prediction
[old]
Isovector longitudinally polarized PDF
CQSM predicts
This means that antiquarks gives sizable positive contribution to Bjorken S.R.
denied by the HERMES analysis of semi-inclusive DIS data
However, HERMES analysis also denies negative strange-quark polarization
favored by the global-analysis heavily depending on inclusive DIS data !