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5-quark components in baryons

5-quark components in baryons. Bing-Song Zou Institute of High Energy Physics Beijing. Outline. Success and failure of classic 3q model 5-quark components in the proton 5-quark components in ½- excited baryons Conclusion. △ -. △ 0. △ +. △ ++. s. (uuu). (ddd). n (udd). p (uud).

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5-quark components in baryons

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

  2. Outline • Success and failure of classic 3q model • 5-quark components in the proton • 5-quark components in ½- excited baryons • Conclusion

  3. △- △0 △+ △++ s (uuu) (ddd) n(udd) p(uud) (udd) (uud) 0 *- *+ (uus) (dds) (uds) 0(uds) +(uus) -(dds) I3 0 *- *0 (uss) (dss) -(dss) 0(uss) - (sss) • Success and failure of classic 3q model SU(3) 3q-quark model for baryons 1/2 + spin-parity 3/2+ Successful for spatial ground states ! Prediction m- 1670 MeV experiment m- 1672.45 0.29 MeV

  4. Two outstanding problems for excited baryons • Mass 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 - ~ L*(1405) • harmonic oscillator ( 2n + L + 3/2 ) hw • The number of predicted states is much less than 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 > + e1 | n ( udd ) p+ (`du ) > A.Thomas, J.Speth + e2 | D++ ( uuu ) p- (`ud ) > +…

  8. Meson cloud model including strangeness: • | p > ~ | uud > + e1 | n ( udd ) p+ (`du ) > + e2 | D++ ( uuu ) p- (`ud ) > • + e’ | L (uds) K+ (`su ) > + … • Predictions for the proton: • Strange spin : Ds < 0 • Strange magnetic moment : ms < 0 • Strange radii : rs < 0 • The most recent analysis of data for strange spin •  Ds = -0.05 ~ -0.1 • D. de Florian et al., Phys. Rev. D71 (2005) 094018

  9. The strange magnetic moment ms and radii rsfrom 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 ms and rs 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 ms and rs

  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 L (uds) K+ (`su ) ! | p > ~ | uud > + e1| [ud][ud]`d > + e2 | [ud][us]`s > + … `S u S u `S S u u d d Pentaquark vs Meson Cloud

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

  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. N*(1535) in J/y p K-`L + c.c. Nx Nx Events/10MeV (Arbitrary normalization) PS, eff. corrected Nx 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/y p`N*  p (K-`L) / p (`ph) gN*KL /gN*ph /gN*pp ~ 1.3 : 1 : 0.6 Smaller N*(1535) BW mass

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

  18. Total cross section and theoretical results with N*(1535), N*(1650), N*(1710), N*(1720) pp  p K+L 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 `q ½ - [ud] [us] u `q ½+ [ud] [ud] u S d `q `q }L=0 }L=1 u d u d N*(1535) ~ uud (L=1) + e [ud][us]`s + … N*(1440) ~ uud (n=1) + x [ud][ud]`d + … L*(1405) ~ uds (L=1) + e [ud][su]`u + … Larger [ud][us]`s component in N*(1535) makes it coupling stronger to Nh & KL, weaker to Np & KS, and heavier ! B.C.Liu, B.S.Zou, PRL 96(2006)042002

  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！

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