DPyC 2007Roelof Bijker, ICN-UNAM1 An Unquenched Quark Model of Baryons 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)

DPyC 2007Roelof Bijker, ICN-UNAM2 Baryons Baryons ) QCD qqq decuplet & octet (Gell-Mann, Zweig) Spin-statistics paradox in  ++ ) color (Greenberg, Han & Nambu) Valence quark model (Dalitz, Becchi & Morpurgo, Isgur & Karl, …) QCD ) V NN ? Baryons ) V NN ?

DPyC 2007Roelof Bijker, ICN-UNAM3 Nuclear Physics

DPyC 2007Roelof Bijker, ICN-UNAM4 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, …

DPyC 2007Roelof Bijker, ICN-UNAM5 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 …

DPyC 2007Roelof Bijker, ICN-UNAM6 Baryon Masses Bijker, Iachello & Leviatan, AP 284, 89 (2000) Nucleon Lambda

DPyC 2007Roelof Bijker, ICN-UNAM7 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 …

DPyC 2007Roelof Bijker, ICN-UNAM8 N(1520) Resonance Collective U(7) PRC 54, 1935 (1996) hCQM JPG 24, 753 (1998)

DPyC 2007Roelof Bijker, ICN-UNAM9 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

DPyC 2007Roelof Bijker, ICN-UNAM10 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

DPyC 2007Roelof Bijker, ICN-UNAM11 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, (2007)

DPyC 2007Roelof Bijker, ICN-UNAM12 Strange EM Form Factors R. Bijker - JPG 32, L49 (2006) arXiv:nucl-th/

DPyC 2007Roelof Bijker, ICN-UNAM13 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/

DPyC 2007Roelof Bijker, ICN-UNAM14 Flavor Asymmetry Gottfried sum rule

DPyC 2007Roelof Bijker, ICN-UNAM15 Extend the CQM to include the effects of quark-antiquark pairs in a general and consistent way

DPyC 2007Roelof Bijker, ICN-UNAM16 Strong QCD Analogy with diatomic molecules Starting point: Valence quarks + Flux tubes Large N C limit of QCD Quenched lattice QCD Heavy quark limit Flux-tube breaking: quark-antiquark pairs

DPyC 2007Roelof Bijker, ICN-UNAM17 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: hadron spectroscopy and OZI rule Strange quark-antiquark pairs in the proton with h.o. wave functions Geiger & Isgur, PRD 55, 299 (1997)

DPyC 2007Roelof Bijker, ICN-UNAM18 Flux Tubes Derek Leinweber (Adelaide)

DPyC 2007Roelof Bijker, ICN-UNAM19 Diagrams

DPyC 2007Roelof Bijker, ICN-UNAM20 Geiger & Isgur, PRD 55, 299 (1997)

DPyC 2007Roelof Bijker, ICN-UNAM21 Extensions Valence quarks 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/ Bijker & Santopinto, nucl-th/

DPyC 2007Roelof Bijker, ICN-UNAM22 Flux-tube Breaking Model

DPyC 2007Roelof Bijker, ICN-UNAM23 Closure Limit Proton Spin

DPyC 2007Roelof Bijker, ICN-UNAM24 Octet Baryons

DPyC 2007Roelof Bijker, ICN-UNAM25 Decuplet Baryons

DPyC 2007Roelof Bijker, ICN-UNAM26 Closure Limit

DPyC 2007Roelof Bijker, ICN-UNAM27 Proton Spin Composition 1980’s1990’s2000’s Naive parton model 3 valence quarks QCD: contributions from sea quarks and gluons.. and orbital angular momentum HERMES, hep-ex/

DPyC 2007Roelof Bijker, ICN-UNAM28 Spin of the Proton Unquenched quark model Creation of quark-antiquark pairs Proton spin Present model:

DPyC 2007Roelof Bijker, ICN-UNAM29 Preliminary Results HERMES Collaboration, hep-ex/

DPyC 2007Roelof Bijker, ICN-UNAM30 Flavor Asymmetry Flavor asymmetry of the nucleon sea Gottfried sum rule with Flavor symmetric sea

DPyC 2007Roelof Bijker, ICN-UNAM31 Results Pauli blocking (Field & Feynman, 1977) too small Pion dressing of the nucleon (Thomas et al., 1983) Meson cloud models Flavor asymmetry Nonperturbative QCD

DPyC 2007Roelof Bijker, ICN-UNAM32 Summary and Conclusions Unquenched quark model Higher Fock components (Riska, Diakonov,...) Flavor content of physical observables Spin of the proton Flavor asymmetry of the nucleon sea First results very promising Future: Electromagnetic and axial form factors of the nucleon and its excited states

DPyC 2007Roelof Bijker, ICN-UNAM33

DPyC 2007Roelof Bijker, ICN-UNAM34

DPyC 2007Roelof Bijker, ICN-UNAM35

DPyC 2007Roelof Bijker, ICN-UNAM36 Closure Limit

DPyC 2007Roelof Bijker, ICN-UNAM37