5-quark components in baryons

Bing-Song Zou

Institute of High Energy Physics Beijing

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

1. Success and failure of classic 3q model

SU(3) 3q-quark model for baryonsSU(3) 3q-quark model for baryons

1/2 + spin-parity 3/2+1/2 + spin-parity 3/2+

Prediction m- 1670 MeV experim

ent m- 1672.45 0.29 MeV

s

I3

n(udd)

p(uud)

-(dds)

0 (uds) 0

+ (uus)

-(dss) 0(uss) (sss)

△0 △- △+ △++

0*- *+

(ddd) (udd) (uud) (uuu)

(dds) (uds) (uus)

*- *0

(uss)(dss)

-

Successful for spatialground states !

Two outstanding problems for excited baryons

• Mass order reverse problem for the lowest 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 - ~ *(1405)

harmonic oscillator ( 2n + L + 3/2 ) hharmonic 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 : missing” baryon states : non-existence / to be observednon-existence / to be observed ? ?

What are effective degrees of freedom ?

(a) 3q (b) hybrid (c) diquark (d) multi-quark

Predicted states: (d) > (b) > (a) > (c)

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)

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 ) > +…

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 : rs < 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

The strange magnetic moment s and radii rs

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) 152001SAMPLE/MIT-Bates: Phys.Lett.B583 (2004) 79

Theory vs experiment for s and rs

Our results

B.S.Zou, D.O.Riska, Phys. Rev. Lett. 95 (2005) 072001D.O.Riska, B.S.Zou, Phys. Lett. B636 (2006) 265C.S.An,D.O.Riska,B.S.Zou, Phys. Rev. C73 (2006) 035207

Theory vs experiment for s and rs

B.S.Zou, D.O.Riska, Phys. Rev. Lett. 95 (2005) 072001

New picture for strangeness in the proton:

Penta-quark configurations [su][ud]

instead of meson cloud (uds) K+ (su ) !

| p > ~ | uud > + [ud][ud]d > + | [ud][us]s > + …

Su

uS

d

u

du

SS

Pentaquark vs Meson Cloud

Baryon spectroscopy from J/ decays at BES/BEPC

Ideal isospin filter

**,*,*,/ NBMBJ

3. 5-quark components in excited baryons

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

)(GeV/c2KΛM

Eve

nts

/10

MeV

Nx

Nx

Nx

)(GeV/c2 MMM KKΛ

PS, eff. corrected

(Arbitrary normalization)

N*(1535) in J/p K-+ c.c.

BES, Int. J. Mod. Phys. A20 (2005)

B.C.Liu, B.S.Zou, nucl-th/0503069, Phys. Rev. Lett. 96 (2006)

From relative branching ratios of

J/pN* p (K-p (p

gN*K/gN*p/gN*p~ 1.3 : 1 : 0.6

Smaller N*(1535) BW mass

(1)

(2)

(3)

Mass of N*(1535)

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)

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

ud

du

q

u

du

qSq ½+

[ud][ud]

}L=1

q ½ -[ud][us]

}L=0

4. Conclusion

• 5-quark components in baryons are important

• Mainly in colored diquark cluster configuration

rather than meson-cloud configuration .

谢谢大家！