1. 5-quark components in baryons Bing-Song Zou Institute of High Energy Physics Beijing

2. Outline 1.Success and failure of classic 3q model 2.5-quark components in the proton 3.5-quark components in ½- excited baryons 4.Conclusion

3. 1.Success and failure of classic 3q model SU(3) 3q-quark model for baryons SU(3) 3q-quark model for baryons 1/2 + spin-parity 3/2+ 1/2 + spin-parity 3/2+ Prediction m  -  1670 MeV experiment m  -  1672.45  0.29 MeV s I3I3 n(udd)p(uud)  - (dds)  0 (uds) 00  + (uus)  - (dss)  0 (uss) (sss) △0△0 △-△- △+△+ △ ++ 00  *-  *+ (ddd) (udd)(uud) (uuu) (dds) (uds) (uus) *-*-  *0 (uss) (dss) -- Successful for spatial ground states !

4. Two outstanding problems for excited baryons Mass order reverse problem for the lowest excited baryonsMass order reverse problem for the lowest excited baryons uud (L=1) ½ - ~ N*(1535) should be the lowest uud (n=1) ½ + ~ N*(1440) uds (L=1) ½ - ~  *(1405) harmonic oscillator ( 2n + L + 3/2 ) h  harmonic oscillator ( 2n + L + 3/2 ) h  The number of predicted states is much less than observedThe number of predicted states is much less than observed “missing” baryon states : non-existence / to be observed ? “missing” baryon states : non-existence / to be observed ?

5. What are effective degrees of freedom ? (a) 3q (b) hybrid (c) diquark (d) multi-quark Predicted states: (d) > (b) > (a) > (c)

6. 2. 5-quark components in the proton Classical picture of the proton Perturbative gluon-sea-quark fluctuation :  u(x) =  d(x),  s(x) = s(x)

7. Flavor asymmetry of light quarks in the nucleon sea Deep Inelastic Scattering (DIS) + Drell-Yan (DY) process  d –  u ~ 0.12 Meson cloud model: | p > ~ | uud > +   | n ( udd )  + (  du ) > A.Thomas, J.Speth +   |  ++ ( uuu )  - (  ud ) > +…

8. Meson cloud model including strangeness: | p > ~ | uud > +   | n ( udd )  + (  du ) > +   |  ++ ( uuu )  - (  ud ) > +  ’ |  (uds) K + (  su ) > + … Predictions for the proton: Strange spin :  s < 0 Strange magnetic moment :  s < 0 Strange radii : r s < 0 The most recent analysis of data for strange spin   s = -0.05 ~ -0.1 D. de Florian et al., Phys. Rev. D71 (2005) 094018

9. The strange magnetic moment  s and radii r s from parity violating electron scattering G0,HAPPEX/CEBAF, SAMPLE/MIT-Bates, A4/MAMI HAPPEX/CEBAF, Phys.Rev.Lett. 96 (2006) 022003 G0/CEBAF, Phys.Rev.Lett. 95 (2005) 092001 A4/MAMI, Phys.Rev.Lett. 94 (2005) 152001 SAMPLE/MIT-Bates: Phys.Lett.B583 (2004) 79

10. Theory vs experiment for  s and r s Our results B.S.Zou, D.O.Riska, Phys. Rev. Lett. 95 (2005) 072001 D.O.Riska, B.S.Zou, Phys. Lett. B636 (2006) 265 C.S.An,D.O.Riska,B.S.Zou, Phys. Rev. C73 (2006) 035207

11. Theory vs experiment for  s and r s

12. B.S.Zou, D.O.Riska, Phys. Rev. Lett. 95 (2005) 072001 New picture for strangeness in the proton: Penta-quark configuration  s [su][ud] instead of meson cloud  (uds) K + (  su ) ! | p > ~ | uud > +    [ud][ud]  d > +   | [ud][us]  s > + … SS u u SS d u du SS SS Pentaquark vs Meson Cloud

13. Baryon spectroscopy from J/  decays at BES/BEPC Ideal isospin filter 3. 5-quark components in excited baryons

14. The nature of the lowest ½- resonance N*(1535) BES Collaboration, H.B.Li, B.S.Zou, H.C.Chiang, G.X.Peng, J.X.Wang, J.J.Zhu, Phys. Lett. B510 (2001) 75

15. Events/ 10 MeV NxNx NxNx NxNx PS, eff. corrected (Arbitrary normalization) N*(1535) in J/    p K -  + c.c. BES, Int. J. Mod. Phys. A20 (2005)

16. B.C.Liu, B.S.Zou, nucl-th/0503069, Phys. Rev. Lett. 96 (2006) From relative branching ratios of J/    p  N*  p (K-  p (  p  g N*K  /g N*p  /g N*p  ~ 1.3 : 1 : 0.6 Smaller N*(1535) BW mass

17. (1) (2) (3) Mass of N*(1535)

18. Total cross section and theoretical results with N*(1535), N*(1650), N*(1710), N*(1720) pp  p K +  Tsushima,Sibirtsev,Thomas, PRC59 (1999) 369, without including N*(1535)

19. A.Zhang, Y. Liu, P. Huang, W. Deng, X.Chen, S.L. Zhu, hep-ph/0403210 : 1/2- and 1/2+ octet N* pentaquarks have similar masses in Jaffe-Wilczek diquark model N*(1535) ~ uud (L=1) +  [ud][us]  s + … N*(1440) ~ uud (n=1) +  [ud][ud]  d + …  *(1405) ~ uds (L=1) +  [ud][su]  u + … Larger [ud][us]  s component in N*(1535) makes it coupling stronger to N  & K , weaker to N  & K  and heavier ! B.C.Liu, B.S.Zou, PRL 96(2006)042002 u d du qq u du qq SS  q ½+ [ud] } L=1  q ½ - [ud] [us] } L=0

20. 4. Conclusion 5-quark components in baryons are important Mainly in colored diquark cluster configuration rather than meson-cloud configuration. 谢谢大家！