1 5-quark components in baryons and evidence at BES 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  -   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 -- Lutz’s talk

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 = ~ -0.1 D. de Florian et al., Phys. Rev. D71 (2005)

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) G0/CEBAF, Phys.Rev.Lett. 95 (2005) A4/MAMI, Phys.Rev.Lett. 94 (2005) 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) D.O.Riska, B.S.Zou, Phys. Lett. B636 (2006) 265 C.S.An,D.O.Riska,B.S.Zou, Phys. Rev. C73 (2006)

11 B.S.Zou, D.O.Riska, Phys. Rev. Lett. 95 (2005) 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

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

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 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)

15 B.C.Liu, B.S.Zou, nucl-th/ , 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

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

17 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)

18 A.Zhang, Y. Liu, P. Huang, W. Deng, X.Chen, S.L. Zhu, hep-ph/ : 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) u d du qq u du qq SS  q ½+ [ud] } L=1  q ½ - [ud] [us] } L=0

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

20 J/  decay branching ratio * 10 4  p               p N*(1535)  1/2- 10            It is very important to check whether under the  and  peaks there are ½- components ? } SU(3) breaking } SU(3) allowed

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

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！