NSTAR 2007Roelof Bijker, ICN-UNAM1 Flavor Asymmetry of the Nucleon Sea in an Unquenched Quark Model Introduction Degrees of freedom Unquenched quark model

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  • 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)
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  • 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,
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  • 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
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  • NSTAR 2007Roelof Bijker, ICN-UNAM4 N(1520) Resonance Collective U(7) PRC 54, 1935 (1996) hCQM JPG 24, 753 (1998)
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  • 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
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  • 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
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  • 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)
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  • NSTAR 2007Roelof Bijker, ICN-UNAM8 Flavor Asymmetry Gottfried sum rule
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  • NSTAR 2007Roelof Bijker, ICN-UNAM9 Extend the CQM to include the effects of quark-antiquark pairs in a general and consistent way
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  • 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 CQMs Strange quark-antiquark pairs in the proton with h.o. wave functions Geiger & Isgur, PRD 55, 299 (1997)
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  • NSTAR 2007Roelof Bijker, ICN-UNAM11 Diagrams
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  • NSTAR 2007Roelof Bijker, ICN-UNAM12 Geiger & Isgur, PRD 55, 299 (1997)
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  • 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
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  • NSTAR 2007Roelof Bijker, ICN-UNAM14 Flux-tube Breaking Model
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  • NSTAR 2007Roelof Bijker, ICN-UNAM15 Closure Limit Proton Spin
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  • NSTAR 2007Roelof Bijker, ICN-UNAM16 Closure Limit
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  • NSTAR 2007Roelof Bijker, ICN-UNAM17 Flavor Asymmetry Flavor asymmetry of the nucleon sea Gottfried sum rule with Flavor symmetric sea
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  • 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
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  • NSTAR 2007Roelof Bijker, ICN-UNAM19 Proton Spin Crisis 1980s1990s2000s Naive parton model 3 valence quarks QCD: contributions from sea quarks and gluons.. and orbital angular momentum HERMES, hep-ex/0609039
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  • NSTAR 2007Roelof Bijker, ICN-UNAM20 Spin of the Proton Unquenched quark model Creation of quark-antiquark pairs Proton spin Present model:
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  • NSTAR 2007Roelof Bijker, ICN-UNAM21 Preliminary Results HERMES Collaboration, hep-ex/0609039
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  • 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
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  • NSTAR 2007Roelof Bijker, ICN-UNAM23
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  • NSTAR 2007Roelof Bijker, ICN-UNAM24 Octet Baryons
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  • NSTAR 2007Roelof Bijker, ICN-UNAM25 Decuplet Baryons