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1 5-quark components in baryons and evidence at BES Bing-Song Zou Institute of High Energy Physics Beijing
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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
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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 - 1672.45 0.29 MeV s I3I3 n(udd)p(uud) - (dds) 0 (uds) 00 + (uus) - (dss) 0 (uss) (sss) △0△0 △-△- △+△+ △ ++ 00 *- *+ (ddd) (udd)(uud) (uuu) (dds) (uds) (uus) *-*- *0 (uss) (dss) -- Successful for spatial ground states !
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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 ?
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5 What are effective degrees of freedom ? (a) 3q (b) hybrid (c) diquark (d) multi-quark -- Lutz’s talk
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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)
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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 ) > +…
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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 = -0.05 ~ -0.1 D. de Florian et al., Phys. Rev. D71 (2005) 094018
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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) 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
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10 Theory vs experiment for s and r s 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
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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 (uds) K + ( su ) ! | p > ~ | uud > + [ud][ud] d > + | [ud][us] s > + … SS u u SS d u du SS SS Pentaquark vs Meson Cloud
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12 Baryon spectroscopy from J/ decays at BES/BEPC Ideal isospin filter 3. 5-quark components in excited baryons
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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
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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)
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15 B.C.Liu, B.S.Zou, nucl-th/0503069, 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
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16 (1) (2) (3) Mass of N*(1535)
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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)
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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 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 u d du qq u du qq SS q ½+ [ud] } L=1 q ½ - [ud] [us] } L=0
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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- ?
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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
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21 (ssq) - Baryon Spectroscopy Theory is totally not challenged due to lack of data ! Capstick&Isgur PRD34(1986)2809 KAON@TRIUMF BESIII@BEPC2 Zhu S L’s prediction of pentaquark state
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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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