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PentaquarksPentaquarks: : 五夸克五夸克态态

Bo-Qiang Ma ( 马伯强马伯强 )) PKU PKU (( 北京大学物理学院北京大学物理学院 ))

August 14,August 14, 200 20044talk at CCAST Wokshop on QCD and RHIC Physics talk at CCAST Wokshop on QCD and RHIC Physics

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In Collaboration with B. Wu Hep-ph/0312041, PRD69(2004)077501

Hep-ph/0312326, PLB586 （ 2004 ） 62

Hep-ph/0311331, Hep-ph/0402244

Hep-ph/0408121 all to appear in PRD

Also HERMES Collaborators (Y.Mao et al.): PLB585(2004)213.

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A Break Through of Hadron Physics in 2003 ：

Pentaquark 五夸克态

• Second Item of Top 10 Physics News in 2003

In News:In News:• Nature Science Update: “…could have

important implications for understanding of the early universe”

• BBC News: “should have far-reaching consequences for understanding the structure of matter”

• MSN: “a new classification of matter…”

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Search for Exotic Baryon States

• Standard Quark Model– classifies hadrons as

• mesons ( ) • baryons ( )

– also allows “non-standard” or exotic hadron states

• multiquark mesons ( )• multiquark baryons ( ) -> appear as baryon resonances• hybrid states ( )• dibaryons ( )• glueballs

-> no convincing previous evidence for exotic baryon states before 2003.

qqqqq

qqqq

qqqqq

or qqg qqqg

qqqqqq

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Baryon States

•All baryons observed before– classified as singlets, octets and decuplets of SU(3) flavor group -> constructed of 3 quarks only, - may have higher orbital angular momentum– have strangeness from S=-3 to S=0

• Exotic Baryons with S=+1– cannot be formed from only 3 quarks– belong to higher SU(3) multiplet

baryon octet with JP=½+

baryon decuplet with JP=(3/2)+

I

Y

Z0

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Previous Searches for Exotic Baryons

• Ideally: kaon-nucleon (KN) scattering • started in 1966 at BNL -> “clear” resonance peak found in K+p at M=1.91 GeV and =180 MeV• searches: partial wave analyses in KN scattering

– candidates: isoscalar Z0(1780) and Z0(1865)

-> give poor evidence (PDG)

• dropped from PDG listings after 1986• reasons for failure:

– KN (in)elastic scattering at p(K) corresponding to 1.74 MZ 2.16 GeV

– resonance widths large: 70 Z 845 MeV

– MIT bag model predictions: MZ 1.7 GeV

• (1405): molecular meson-baryon state ?

– interpretation problematic: could be -> ambiguity remains

R. Cool et al., PRL 17, 102 (1966)

BNL 1966

uudsuuds

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(1405) as 5-quark state

Jue-Ping Liu, Z.Phys.C 22(1984)171

• Using QCD sum rule method to calculate

the 5-quark component of (1405)

• But cannot rule out miminal uds component in the state

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Pentaquark StatesPentaquark States

• Predictions of pentaquark states with both strange and charm (by Lipkin et al.),

no evidence found in experimental searches for more than ten years.

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Prediction in Chiral Soliton Model

• all baryons are rotational excitations of a rigid object

• reproduces mass splittings witin 1% of

– baryon octet (JP=½+) and decuplet (JP=3/2+)

• predicts new anti-decuplet (among many Ncartifacts)

• “only one” free parameter

D. Diakonov, V.Petrov, M.Polyakov, Z. Phys. A 359, 305 (1997)

Identifying P11(1710) as member of anti-decuplet:

prediction for M1.53 GeV 15 MeV

I=0 S=+1 JP=½+

with

K0 p or K+n

the 3 corners are exotic

or or

pK0 or nK+

Based on older predictions:Manohar(1984); Chemtob (1984); Praszalowicz (1987)

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Suggestion for the existence of higher multipletsSuggestion for the existence of higher multiplets

M.-L.Yan and X.-H.Meng, Commun. Theor. Phys. 24 (1995) 435

• The corrections to the Gell-Mann-Okubo relations of baryons masses in SU(3) Skyrmen model are considered.

• The results could be regarded as a signal for the existence of the SU(3) rotation excitation states of baryons: 27-plet, 10*-let, and 35-let.

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Nothing is “Exotic” in the Chiral Solition PictureNothing is “Exotic” in the Chiral Solition Picture

• Baryons are “solitons” in the chiral fields.

• No baryon is “exotic” except that it has different quantum numbers compared to other baryons.

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““Exotic”-baryon (Pentaquark) DefinationExotic”-baryon (Pentaquark) DefinationH.Gao and B.-Q. MaH.Gao and B.-Q. Ma

Mod. Phys. Lett. A 14 (1999) 2313Mod. Phys. Lett. A 14 (1999) 2313

• A pentaquark qqqqq state can be clearly A pentaquark qqqqq state can be clearly distinguished from the conventional qqq-baryon distinguished from the conventional qqq-baryon state or their hybrids if the flavor of q is different state or their hybrids if the flavor of q is different from any of the other four quarks: from any of the other four quarks:

minimal Fock state of pentaquarkminimal Fock state of pentaquark

• Possible existence of uudds and uuuds states are Possible existence of uudds and uuuds states are suggested.suggested.

-

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Suggestion for search of pentaquark uudds stateSuggestion for search of pentaquark uudds statein physics processin physics process

H.Gao and B.-Q. MaH.Gao and B.-Q. Ma Mod. Phys. Lett. A 14 (1999) 2313Mod. Phys. Lett. A 14 (1999) 2313

• Suggested:n Θ

missing mass method to construct Θ

• SPring8 and CLAS experiments: sub-process

n (Kn) an additional K is detected to reduce background for the missing

mass spectrum and real photon is used instead of virtual photon.

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What is a Pentaquark

A pentaquark is a hadron that is composed of 4 valence quarks and one valence antiquark. It has strangeness S=+1 and is tightly bound by the strong hadronic force. -> constitutes a new form of matter

HERMES Experiment

Decay Mode:Ks p or K+n

0D X XpK

14Yajun Mao for HERMES Collaboration, YITP Multi-quark Workshop, Feb. 17-19, 2004

HERMES Result: Talk by Yajun Mao at Tokyo

Resonance is observed at

1528 2.6 2.1 MeV

Width is

FWHM = 19 5 2 MeV

Naïve significance in ±2

True significance

Unbinned fit is used: result doesn’t depend on bin size and starting point

b

s

N

N

s

s

N

N

144/56

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Where else to look for Production

• ideally: K0p and K+n – mass range too low for kaon beams high for factory of kaons

• less ideal: collision of non-strange particles– many particles in final states– some are neutral -> complex detectors need

D. Diakonov,priv. commun. (May 2003)

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Summary of recent experimentsSummary of recent experiments

world-average: : 15322.4 MeV

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Summary of recent Evidence for

Next:• Determine width, other quantum numbers (parity!).

Experiments

ResultsMass Width (MeV) (Mev)

SPring8DIANACLASSAPHIRITEP ()HERMESKN elastic

1540 10 5 25 4.61

1539 2 “few” 8 4.4

1542 2 5 FWhM= 21 5.30.5

1540 4 225 4.8

1533 5 < 20 6.7

1526 2 2 5.60.5

few MeV !

One theory

(QSM)

1530 MeV MeVI=0 S=+1 JP=½+

( / )s bN N

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Summary of Null Results

0 null results published, only 3 on arXiv so far⇒ need null results to be published

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no evidence no evidence forfor KK++p p in HERMESin HERMES

Suggesting ++ Being Isosinglet

I=0 is likely

I=2 is ruled out

I=1 is unlikely, but cannot be

ruled out

X.Chen, Y.Mao, and B.Q.Ma,

hep-ph/0407381

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Pentaquark States from Theory:Pentaquark States from Theory:anti-decuplet in chiral soliton models-1st version

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Prediction of Diquark modelPrediction of Diquark model

[ud]2s

*0

*- *0

S

I3

3/2(1750)

+(1530)

1-1

-1

1

[us]2d[ds]2u

R.L. Jaffe and F. Wilczek, PRL91 (2003) 232003

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Evidence for New Pentaquark?Evidence for New Pentaquark?

SM: M(*--) = 2070 MeV

[qiqj]2q: M(*--) = 1750 MeV

C. Alt et al., hep-ex/0310014NA49 at CERN pp *-- X, *0 X, - - - +s = 17,2 GeV

1,862 0,002 GeV

But: It is not what theory predicted !

D. Diakonov et al., hep-ph/0310212

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uud ds

sdd.. sdu.. suu(dd+ss)

*0

*- *0

S

I3

(1754)

3/2(1862)

+(1539)

Anti-Decuplet in Chiral Soliton ModelAnti-Decuplet in Chiral Soliton Model - Version 2

1-1

-1

N(1647)

ssu udssd du ssd (uu+dd) ssu..

duu(dd+ss)

sdu..

1

108 MeV

D. Diakonov and V. Petrov hep-ph/0310212

B. Wu and Ma, hep-ph/0311331, PRD

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Where are the missing members of antidecuplet?Where are the missing members of antidecuplet?

• For baryons with spin ½ and + parity, there is no N around, and a weak evidence for (1770),

so Diakonov and Petro (hep-ph/0310212) suggeted a missing N around 1650-1690 MeV;

the position of N(1710) is not at M=1710 MeV, but some where around M=1650 to 1690 MeV, suggested by Arndt et al(nucl-th/0312126) .

• We noticed ( hep-ph/9311331) that there are candidates of N(1650) and (1750) with spin ½ and negative (–) parity, in PDG

This may suggest a negative parity for antidecuplet members in the chiral soliton model:

parity in chiral solition has two parts: quantized part with positive parity and classical part with unknown parity;

the collective coordinate quantization can not inevitably fix the parity of the corresponding baryons.

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The width formula and the widths in the case of negative parityThe width formula and the widths in the case of negative parity

decay width is excellent for S(1750), but poor for N(1650) , possible solution:

SU(3) breaking for baryons with strangeness,

or there is a missing N resonance around 1650 with narrow width.

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Theories of Theories of positivepositive parity for parity for • Chiral Soliton Models (old version) Diakonov-Petrov-Polyakov, ZPA359(1997)305

• Analysis in Quark Model Stancu-Riska, PLB575(2003)242

• Diquark Cluster Model Jaffe-Wilczek, PRL91(2003)232003

• Diquark-Triquark Model Karliner-Lipkin, PLB575(2003)249

• Inherent Nodal Structure Analysis Y.-x.Liu, J.-s.Li, and C.-g. Bao, hep-ph/0401197

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• Naive Quark Model Jaffe (1976)

• Some Quark Models Capstick-Page-Roberts, PLB570(2003)185

Huang-Zhang-Yu-Zhou, hep-ph/0310040 ， PLB

• QCD Sum Rules Zhu, PRL91(2003)232002, Sugiyama-Doi-Oka, hep-ph/0309271

• Lattice QCD Sasaki, hep-ph/0310014, Csikor et al, hep-ph/0309090,

but we heard difference voices recently

Theories of Theories of negativenegative parity for parity for

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Where is the answer? Where is the answer? Experiment!Experiment!

• Many suggestions on detecting the parity

Oh-Kim-Lee, hep-ph/0310019

Zhao, hep-ph/0310350

Liu-Ko-Kubarovsky, nucl-th/0310087

Nakayama-Tsushima, hep-ph/0311112

Thomas-Hicks-Hosaka, hep-ph/0312083 ……

• Measurement of parity is crucial to test theories

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What else if I=0 or S=1/2What else if I=0 or S=1/2

• Answer: Most theories would need revision!

Would be a new surprise!

//

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Predictions of New PentaquarksPredictions of New Pentaquarks -27-plet

Figure from Wu & Ma, PRD69(2004)077501.

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The mass splitting of the 27-plet The mass splitting of the 27-plet from chiral solitonsfrom chiral solitons

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The widths of the 27-plet The widths of the 27-plet baryonsbaryons

SU(3) Symmetric Case

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The picture of the 27-plet The picture of the 27-plet baryons:baryons:

non-exotic members are well establishednon-exotic members are well established

We suggest that the quantum numbers of is JP=(3/2)+

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Many new pentaquarksMany new pentaquarks to be discoveredto be discovered

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Predictions ofPredictions of

• Walliser-Kopeliovich, hep-ph/0304058

mass=1650/1690 MeV

• Borisyuk-Faber-Kobushkin, hep-ph/0307370

mass=1595 MeV, width=80 MeV

• Wu-Ma, PLB586(2004)62

mass=1600 MeV, width less than 43 MeV

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Predictions of New PentaquarksPredictions of New Pentaquarks -35-plet

Figure from Wu & Ma, PRD, to appear .

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Mass splitting of 35-plet from chiral Mass splitting of 35-plet from chiral solitonssolitons

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The widths of the 35-plet baryonsThe widths of the 35-plet baryons

SU(3) Symmetric Case

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Prediction of Pentaquarks Prediction of Pentaquarks in SU(4) Chiral Solition Modelin SU(4) Chiral Solition Model

B.Wu and B.-Q.Ma, hep-ph/0402244,

PRD to appear

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Experiment Evidence at H1Experiment Evidence at H1

hep-ex/0403017 hep-ex/0403017

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The pentaquark uuddcThe pentaquark uuddc• Prediction of the mass of the ground uuddcbar: Prediction of the mass of the ground uuddcbar:

m=2704 MeV, as pD statem=2704 MeV, as pD state Wu-Ma, hep-ph/0402244Wu-Ma, hep-ph/0402244

• Observation by H1 Collaboration: m=3099 MeVObservation by H1 Collaboration: m=3099 MeV

hep-ex/0403017 hep-ex/0403017

can be considered as pD* statecan be considered as pD* state

• From M(D*-D)~300 MeV, the observed uuddcbar can be From M(D*-D)~300 MeV, the observed uuddcbar can be

considered as an excited state (chiral partner) of the considered as an excited state (chiral partner) of the

predicted ground pentaquark state predicted ground pentaquark state

M. Nowak et al, TPJU-4/2004, BNL-NTBNL-NT-04/10M. Nowak et al, TPJU-4/2004, BNL-NTBNL-NT-04/10

__

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ConclusionsConclusions

• The discovery of pentaquark The discovery of pentaquark ++ ，， if confirmed, if confirmed,

opens a new window to understand the basic opens a new window to understand the basic

structure of matter. structure of matter.

• Measurement of the parity, isospin and spin of Measurement of the parity, isospin and spin of ++

is crucial to test different theories is crucial to test different theories

• There could be new pentaquark states waiting for There could be new pentaquark states waiting for

discoverydiscovery