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5-quark components in baryonsand evidence at BES
Bing-Song Zou
Institute of High Energy Physics Beijing
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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
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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 !
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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 ? ?
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What are effective degrees of freedom ?
(a) 3q (b) hybrid (c) diquark (d) multi-quark
-- Lutz’s talk
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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)
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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 ) > +…
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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
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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
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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
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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
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Baryon spectroscopy from J/ decays at BES/BEPC
Ideal isospin filter
**,*,*,/ NBMBJ
3. 5-quark components in excited baryons
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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
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)(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)
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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
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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)
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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
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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- ?
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J/ decay branching ratio * 104
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
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(ssq) - Baryon Spectroscopy *
Theory is totally not challenged due to lack of data !
Capstick&IsgurPRD34(1986)2809
KAON@TRIUMF BESIII@BEPC2
Zhu S L’s predictionof pentaquark state