1. NSTAR 2007Roelof Bijker, ICN-UNAM1 Flavor Asymmetry of the Nucleon Sea in an Unquenched Quark Model Introduction Degrees of freedom Unquenched quark model Closure limit; Spin of the proton; Flavor asymmetry of the nucleon sea Summary and conclusions Roelof Bijker (ICN-UNAM) Elena Santopinto (Genova)

2. NSTAR 2007Roelof Bijker, ICN-UNAM2 Constituent Quark Models Baryons: qqq configurations OGE, chiral, collective U(7), hCQM, bags, soliton, Skyrme, NJL, … Nonrelativistic and relativized Ground state baryons: octet & decuplet, ratio of nucleon magnetic moments Photocouplings, helicity amplitudes, form factors, structure functions, strong decays, …

3. NSTAR 2007Roelof Bijker, ICN-UNAM3 Open Problems Relative mass of N(1440) and N(1535) in hoqm OK in collective U(7) and hCQM Spin-orbit splitting of  (1405) and  (1520) Missing resonances Photocouplings of  (1232): ratio OK, but absolute values not Large  decay widths of N(1535),  (1750),  (1670) Low Q 2 behavior of helicity amplitudes …

4. NSTAR 2007Roelof Bijker, ICN-UNAM4 N(1520) Resonance Collective U(7) PRC 54, 1935 (1996) hCQM JPG 24, 753 (1998)

5. NSTAR 2007Roelof Bijker, ICN-UNAM5 EXOTIC (non q 3 ) DEGREES OF FREEDOM Relative mass of N(1440) and N(1535) Spin-orbit splitting of  1405) and  1520) Photocouplings of  (1232) Large  decay widths of N(1535),  (1750) and  (1670) Low Q 2 behavior of helicity amplitudes

6. NSTAR 2007Roelof Bijker, ICN-UNAM6 Exotic Degrees of Freedom Quark-antiquark pairs, e.g. pentaquark, meson cloud (Thomas, Speth, Kaiser, Weise, Oset, Brodsky, Ma, Isgur, …) Higher Fock components (Riska, Diakonov, …) Strange form factors of the proton Proton spin crisis Flavor asymmetry of nucleon sea

7. NSTAR 2007Roelof Bijker, ICN-UNAM7 Strange Form Factors PV electron scattering The strange (anti)quarks come uniquely from the sea: there is no contamination from up or down valence quarks HAPPEX, PRL 98, 032301 (2007)

8. NSTAR 2007Roelof Bijker, ICN-UNAM8 Flavor Asymmetry Gottfried sum rule

9. NSTAR 2007Roelof Bijker, ICN-UNAM9 Extend the CQM to include the effects of quark-antiquark pairs in a general and consistent way

10. NSTAR 2007Roelof Bijker, ICN-UNAM10 Unquenched Quark Model Pair-creation operator with 3 P 0 quantum numbers of vacuum and geometry of flux-tube breaking model Sum over a large tower of intermediate states to preserve the phenomenological success of CQM’s Strange quark-antiquark pairs in the proton with h.o. wave functions Geiger & Isgur, PRD 55, 299 (1997)

11. NSTAR 2007Roelof Bijker, ICN-UNAM11 Diagrams

12. NSTAR 2007Roelof Bijker, ICN-UNAM12 Geiger & Isgur, PRD 55, 299 (1997)

13. NSTAR 2007Roelof Bijker, ICN-UNAM13 Extensions Valence plus glue dominance with quark- antiquark corrections To any initial baryon or baryon resonance To any flavor of the quark-antiquark pair To any model of baryons and mesons Santopinto & Bijker, nucl-th/0701227 Bijker & Santopinto, nucl-th/0703053

14. NSTAR 2007Roelof Bijker, ICN-UNAM14 Flux-tube Breaking Model

15. NSTAR 2007Roelof Bijker, ICN-UNAM15 Closure Limit Proton Spin

16. NSTAR 2007Roelof Bijker, ICN-UNAM16 Closure Limit

17. NSTAR 2007Roelof Bijker, ICN-UNAM17 Flavor Asymmetry Flavor asymmetry of the nucleon sea Gottfried sum rule with Flavor symmetric sea

18. NSTAR 2007Roelof Bijker, ICN-UNAM18 Results Pauli blocking (Field & Feynman, 1977) too small Pion dressing of the nucleon (Thomas et al., 1983) Meson cloud models Flavor asymmetry Nonperturbative QCD

19. NSTAR 2007Roelof Bijker, ICN-UNAM19 Proton Spin Crisis 1980’s1990’s2000’s Naive parton model 3 valence quarks QCD: contributions from sea quarks and gluons.. and orbital angular momentum HERMES, hep-ex/0609039

20. NSTAR 2007Roelof Bijker, ICN-UNAM20 Spin of the Proton Unquenched quark model Creation of quark-antiquark pairs Proton spin Present model:

21. NSTAR 2007Roelof Bijker, ICN-UNAM21 Preliminary Results HERMES Collaboration, hep-ex/0609039

22. NSTAR 2007Roelof Bijker, ICN-UNAM22 Summary and Conclusions Unquenched quark model: Higher Fock components (Riska, Diakonov,...) Flavor content of physical observables Flavor asymmetry of the nucleon sea Spin of the proton First results very promising Future: Electromagnetic and axial form factors of the nucleon and its excited states

23. NSTAR 2007Roelof Bijker, ICN-UNAM23

24. NSTAR 2007Roelof Bijker, ICN-UNAM24 Octet Baryons

25. NSTAR 2007Roelof Bijker, ICN-UNAM25 Decuplet Baryons