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5-quark components in baryons and evidence at BES

5-quark components in baryons and evidence at BES. 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).

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5-quark components in baryons and evidence at BES

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  1. 5-quark components in baryonsand evidence at BES 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 -- Lutz’s talk

  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. 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

  12. 3. 5-quark components in excited baryons Baryon spectroscopy from J/y decaysat BES/BEPC Ideal isospin filter

  13. 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

  14. 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)

  15. 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

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

  17. 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)

  18. 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

  19. The new picture for the ½ - octet predicts： L* [us][ds]`s ~ 1575 MeV S* [us][du]`d ~ 1360 MeV X* [us][ds]`u ~ 1520 MeV MpL L*(1570) ½- ? H.X.Yang, Ph.D thesis (IHEP,2001) S*(1360)1/2- ?

  20. J/y decay branching ratio * 104 `p D(1232)+ 3/2+ < 1 `S- S(1385)+ 3.1  0.5 `X+ X(1520)- 5.9  1.5 `p N*(1535)+ 1/2- 10  3 `S- S(1360)+ ? `X+ X(1530)- ? It is very important to check whether under the S(1385) and X(1520) peaks there are ½- components ? } SU(3) breaking } SU(3) allowed

  21. (ssq) - Baryon Spectroscopy Capstick&Isgur PRD34(1986)2809 Zhu S L’s prediction of pentaquark state Theory is totally not challenged due to lack of data ! BESIII@BEPC2 KAON@TRIUMF

  22. 4. Conclusion • 5-quark components in baryons are important • mainly in colored diquark cluster configuration • rather than meson-cloud configuration • Predictions can be checked by BES 谢谢大家！

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