BESII Results onHadron Spectroscopy

Shan JIN(for BES Collaboration)

Institute of High Energy Physics (IHEP)jins@mail.ihep.ac.cn

QCD and Hadronic PhysicsBeijing, June 16, 2005

Multi-quark State, Glueball and Hybrid

Hadrons consist of 2 or 3 quarks ：

Naive Quark Model ：

New forms of hadrons:• Multi-quark states ： Number of quarks > ＝ 4 • Hybrids ： qqg ， qqqg …

• Glueballs ： gg ， ggg …

Meson （ q q ）

Baryon （ q q q ）

Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established.

However, during the past two years, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model.

Most of them are multi-quark candidates. Searching for multi-quark states becomes the hottest topic in the hadron spectroscopy.

J/ decays are an ideal factory to search for and study light exotic hadrons:

The production cross section of J/ is high.

The production BR of hadrons in J/ decays are one order higher than ’ decays (“12% rule”).

The phase space to 1-3 GeV hadrons in J/ decays are larger than decays.

Exotic hadrons are naively expected to have larger or similar production BR to conventional hadrons in J/ decays.

Clean background environment compared with hadron collision experiments, e.g., “JP, I” filter.

BESII

VC: xy = 100 m TOF: T = 180 ps counter: r= 3 cm MDC: xy = 220 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.5 % = 7.9 mr B field: 0.4 T p/p=1.7%(1+p2) z = 2.3 cm

World J/ and (2S) Samples (106)

J/ (2S)

0

10

20

30

40

50

60

MarkI I I DM2 BES I BES I I

0

2

4

6

8

10

12

14

MKI MKII MKIII CBAL BESI BESII

Outline Multi-quark Candidates at BESII

• A possible bound state: mass threshold enhancement in and new observation of X(1835).

• mass threshold enhancement in

• mass threshold enhancement in – evidence of a K bound/resonant state.

• Search for pentaquark Θ+(1540)

Scalar Mesons at BESII

• σ, κ, f0(980), f0(1370), f0(1500), f0(1710), f0(1790)

Evidence of new N*(2065) at BESII

pp

ppJ /

pKJ /K

p pKJ /

pp

A possible ppbar bound state: ppbar mass threshold enhancement

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

J/pp

M(pp)-2mp (GeV)

0 0.1 0.2 0.3

3-body phase space acceptance

2/dof=56/56

acceptance weighted BW +3 +5

10 25

pp

BES II

Phys. Rev. Lett. 91, 022001 (2003)   

With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:

much weaker than what BES observed !

NO strong dynamical threshold enhancement in cross sections (at LEAR)

pp

pp

pmppM 2)(

|M|2 |M|2BES BES

elasticelasticM ~|| 2 annlabann PM ~|| 2

Both arbitrary normalization Both arbitrary normalization

Any inconsistency? NO!

For example: with Mres = 1859 MeV, Γ = 30 MeV, J=0, BR(ppbar) ~ 10%, an estimation based on:

At Ecm = 2mp + 6 MeV ( i.e., pLab = 150 MeV ), in elastic process, the resonant cross section is ~ 0.6 mb : much smaller than the continuum cross section ~ 94 20 mb .

Difficult to observe it in cross sections experimentally.

4/)(4

)(4

)12)(12(

)12(22

2

22

2

21

rescm

outin

pcmres mE

BB

mE

c

SS

J

pp

J/ decays do not suffer large t-channel “background” as ppbar collision.

>>

p p p p

p

p p p p

p

/J

In ppbar collision, the background is much lager (I)

A.Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G. Meißner, A.W. Thomas, hep-ph/0411386

P-waveI=0 S-wave

I=1 S-wave

In ppbar elastic scattering, I=1 S-wave dominant,while in J/ radiative decays I=0 S-wave dominant.

ppbar elastic cross section near threshold

In ppbar collision, the background is much lager (II)

So, the mechanism in ppbar collision is quite different from J/ decays and the background is much smaller in J/ decays

It would be very difficult to observe an I=0 S-wave ppbar bound state in ppbar collisions if it exists.

J/ decays (in e+e- collider) have much cleaner environment: “JP, I” filter

This narrow threshold enhancement is NOT observed in B decays

The structure in B decays is obviously different from the BES observation:

KppB

Belle

BES II

ppJ /

The structure in B decays is much wider and is not really at threshold. It can be explained by fragmentation mechanism.

Threshold enhancement in J/ decays is obviously much more narrow and just at threshold, and it cannot be explained by fragmentation mechanism.

X(1860) has large BR to ppbar

We (BES) measured:

For a 0-+ meson:

So we would have:

(BR would be even larger if the width is wider)

5107~))1860(())1860(/( ppXBRXJBR

31025.0~))1860(/( XJBR

%144~))1860(( ppXBR

Considering that decaying into ppbar is only from

the tail of X(1860) and the phase space is very small,

such a BR indicates X(1860) has large coupling to ppbar !

The large BR to ppbar suggest it could be an unconventional meson

For a conventional qqbar meson, the BRs decaying into mesons are usually at least one order higher than decaying into baryons.

• There are many examples in PDG.

E.g.

So the large BR to ppbar (with limited phase space from the tail of X(1860)) seems very hard to be explained by a conventional qqbar meson.

310)4.03.1()(

)%9.06.2()(

ppBR

BR

c

c

pp bound state (baryonium)?

+ n +

deuteron:

loosely bound 3-q 3-q color singlets with Md

= 2mp-

baryonium:

loosely bound 3-q 3-q color singlets with M

b = 2mp-?

attractive nuclear force attractive force?

There is lots & lots of literature about this possibility

E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949)

…I.S. Sharpiro, Phys. Rept. 35, 129 (1978)C.B. Dover, M. Goldhaber, PRD 15, 1997 (1977)…A. Datta, P.J. O’Donnell, PLB 567, 273 (2003)]M.L. Yan et al., hep-ph/0405087B. Loiseau et al., hep-ph/0411218…

ppbar bound state in NNbar potential

Paris NNbar potential: ( Paris 93, B. Loiseau et al., hep-ph/0411218, 0501112 )• For 11S0 , there is a bound state: E = - 4.8 - i 26.3 MeV quite close to the BES observation.

However, Julich NNbar model: ( A. Sibirtsev et al., hep-ph/0411386 )• For 11S0 : E = - 104 - i 413 MeV seems quite far away from BES observation.

They both predict an 11S0 ppbar bound state, although they are quantitatively different.

Observations of this structure in other decay modes are desirable.

A possible ppbar bound state: New Observation of X(1835) in

J

Analysis of )( J

' X(1835)5.1

BESII PreliminaryBESII Preliminary

Analysis of )( J

'X(1835)6.0

BESII PreliminaryBESII Preliminary

Observation of X(1835) in

The +- mass spectrum for decaying into +- and

Statistical Significance 7.7

BESII Preliminary

J

J

Mass spectrum fitting

54264obsN

MeVm 7.21.67.1833

MeV7.73.207.67

410)4.04.02.2()()( XBXJB

7.7The +- mass spectrum for decaying into +- and

BESII Preliminary

59.18.0 10)4.00.7()()(:..

ppXBXJBfc

X(1835) could be the same structure as X(1860) indicated by ppbar mass threshold enhancement

X(1835) mass is consistent with the mass of the s-wave resonance X(1860) indicated by the ppbar mass threshold enhancement.

Its width is 1.9 higher than the upper limit of the width obtained from ppbar mass threshold enhancement.

On the other hand, if the FSI effect is included in the fit of the ppbar mass spectrum, the width of the resonance near ppbar mass threshold will become larger.

Fit to J/p pbar including FSI

Include FSI curve from A.Sirbirtsev et al.(hep-ph/ 0411386) in the fit (I=0)

M = 1830.6 6.7 MeV

= 0 93 MeV

ppp mM 2

In good agreement with X(1835)

A Possible ppbar Bound State

X(1835) could be the same structure as ppbar mass threshold enhancement.

It could be a ppbar bound state since it dominantly decays to ppbar when its mass is above ppbar mass threshold.

Its spin-parity should be 0-+: this would be an important test.

Signature of a ppbar Bound State

’ mode is expected to be the most favorable decay mode for a ppbar bound state below ppbar mass threshold ( G.J. Ding and M.L. Yan, hep-ph/

0502127 ):

• There are gluon contents in proton and anti-proton.

’ has strong coupling to gluons.

Observation of mass threshold

enhancement in

p

pKJ /

Observation of an anomalous enhancement near the threshold of mass spectrum at BES IIp

BES II pKJ /

3-body phase space

For a S-wave BW fit: M = 2075 12 5 MeV Γ = 90 35 9 MeV

Phys. Rev. Lett. 93, 112002 (2004)   

Similar enhancement also observed in pK'

4 away from phase space.

Possible Interpretations

FSI ？ Theoretical calculations are needed.

Conventional K* or a multiquark resonance ？• Search for its Kπ 、 Kππ decay modes w

ould help to understand its nature.• We are now studying

J/ KKπ 、 KKππ

K mass threshold enhancement – evidence of a

K bound/resonant state

)(GeV/c2

ΛKM

PS, eff. corrected

MMM KΛK

Observation of a strong enhancement near the threshold of mass spectrum at BES IIK

(Arbitrary normalization)

BES II pKJ /

NX*

A strong enhancement is observed near the mass threshold of MK at BES II.

Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure Nx*has:

Mass 1500~1650MeV

Width 70~110MeV

JP favors 1/2-

The most important is:

It has large BR(J/ψ pNX*) BR(NX* KΛ) 2 X 10-4 ,

suggesting NX* has strong coupling to KΛ.

This enhancement is NOT observed in process at SAPHIR Kp

pKJ

BES

/

Discussion on KΛ mass threshold enhancement NX(1610)

NX(1610) has strong coupling to KΛ:• From (S&D-wave d

ecay) and is a P-wave decay, we can estimate

• From BESII,

• The phase space of NX to KΛ is very small, so such a big BR shows NX has very strong coupling to KΛ, indicating it has a big hidden ssbar component. (5-quark system)

3102)/( ppJBR )1600(/ XpNJ

3100.1)/( XpNJBR

4102~)()/( KNBRpNJBR XX

%20)( KNBR X

Non-observation of NX in suggests an evidence of new baryon:

It is unlikely to be N*(1535). If NX were N*(1535), it should be observed

in process, since:

•

• From PDG, for the N* in the mass range 1535~1750 MeV, N*(1535) has the largest , and from previous estimation, NX would also have almost the largest BR to KΛ.

Also, the EM transition rate of NXto proton is very low.

Kp

Kp)*()*()*( KNBRpNBRKNp

)*( pNBR

A ΛK resonance predicted by chiral SU(3) quark model

Based on a coupled-channel study of ΛK and ΣK states in the chiral SU(3) quark model, the phase shift shows the existence of a ΛK resonance between ΛK and ΣK mass threshold.

( F. Huang, Z.Y. Zhang et al.

hep-ph/0501102 )

Ecm – ( MΛ+MK ) (MeV)

The KΛ mass threshold enhancement NX(1610) could be a KΛ bound/resonant state.

Is the STRONG threshold enhancement universal/naïve in J/ decays ? —— NO !

Actually in many other cases we do NOT see STRONG threshold enhancements !

For example: In J/ decays at BES II

np J /

)( pM

)(KKMpmppM 2)(

KKJ /

)( pKM

pKJ /

0/ ppJ

Searching for pentaquark Θ+(1540) at BESII

Searching for Θ+(1540) at BESII

Upper limits @ 90% C.L.

BR ( (2S) (KSp)(K-n) + (KSp)(K+n))< 0.84X10-5

BR ( J/ (KSp)(K-n) + (KSp)(K+n)) < 1.1 X10-5

(2S) J/

Phys. Rev. D 70, 012004 (2004)   

Light Scalar Mesons at BESII:

σ, κ, f0(980), f0(1370),

f0(1500), f0(1710), f0(1790)

Why are light scalar mesons interesting?

There have been hot debates on the existence of σ and κ .

σ, κ and f0(980) are also possible mutiquark states. They are all near threshold.

Lattice QCD predicts the 0++ scalar glueball mass ~ 1.6 GeV. f0(1500) and f0(1710) are good candidates.

σ at BES BES II observed σ in J/ +-.

Pole position from PWA:

BES II

M

MeVi )42252()39541(

Phys. Lett. B 598, 149 (2004)   

BES II observed in J/K*KKK.

Preliminary PWA result

Pole position:

κ at BES

BES IIPreliminary

MeVi )420~310()840~760(

Important parameters from PWA fit:

Large coupling with KK indicates big component in f0(980)

/J

KKJ /

f0(980) at BES

21.025.021.4

1510165

68965

g

g

MeVg

MeVM

KK

ss

f0(980)

f0(980)

Phys. Lett. B 607, 243 (2005)   

There has been some debate whether f0(1370) exist or not.

f0(1370) clearly seen in J/ , but not seen in J/ .

/J

/J

PWA 0++ components

f0(1370)

NO f0(1370)

f0(1370) at BES

MeV

MeVM

40265

501350

Clear f0(1710) peak in J/ KK.

No f0(1710) observed in J/ !

f0(1710) at BES

KKJ /

/J

f0(1710)

NO f0(1710)

MeV

MeVM

20125

301740

CLKKfBR

fBR%95@13.0

))1710((

))1710((

0

0

Phys. Lett. B 603, 138 (2004)   

A clear peak around 1790 MeV is observed in J/ .

No evident peak in J/ KK. If f0(1790) were the same as f0(1710), we would have:

Inconsistent with what we observed in J/ , KK

New f0(1790) at BES?

/Jf0(1790)

KKJ /?

MeV

MeVM6030

4030

270

1790

5.1~))1710((

))1790((

0

0

KKfBR

fBR

CLKKfBR

fBR%95@13.0

))1710((

))1710((

0

0

f0(1790) is a new scalar.

Phys. Lett. B 607, 243 (2005)   

Scalars in J/ , KK

Two scalars in J/ :

• One is around 1470 MeV, may be f0(1500)?

• The other is around 1765 MeV, is it f0(1790) or a mixture of f0(1710) and f0(1790)?

One scalar f0(1710) in J/ KK.

BES IIPreliminary

/J

?)1500(0f ?)1710(0f

)1710(0f

KKJ /

Phys. Rev. D 68, 052003 (2003)   

f0(1500) at BES

One scalar with a mass = 1466 6 16 MeV is needed in J/ , is it f0(1500)? Why the mass is different from PDG?

No peak directly seen in , KK, , KK.

OZI rule and flavor tagging in J/ hadronic decays

In J/ hadronic decays, an or Φ signal deter

mines the or component, respe

ctively. OZI rule

dduu ss

/J /J

dduu

ss

Unusual properties of f0(1370), f0(1710) and f0(1790)

f0(1710):

• It dominantly decays to KK (not to )

• It is mainly produced together with (not ) • What is it ?

f0(1370) and f0(1790)

• They dominantly decays to (not to KK) • It is mainly produced together with (not ) • What are they ?

Scalar Puzzle Q.Zhao’s talk

dduu

dduu

ss

ss

Evidence of new N*(2065) at BES II

N*(1440)?

N*(1520)

N*(1535)N*(1650)

N*(1675)

N*(1680)

?

MeV

MeVM

4012175

32065 1530

npJ /

BES IIPreliminary

hep-ex/0405030

Summary (I)

BES II has observed several strong mass threshold enhancements in J/ decays.

Why strong mass threshold structures are important?

Multiquark states may be only observable near mass thresholds with limited decay phase space.

Otherwise, it might be too wide to be observed as a resonance s

ince it can easily fall apart into two or more mesons.

I can see f0(980)

broadresonance or phase space?

any broadresonanceunder other peaks?

I can see broad under other peaks

Summary (II)

A unique very narrow and strong mass threshold enhancement is observed in decays at BES II:• It is not observed in cross sections.• It is not observed in B decays.• Its large BR to suggests it be a bound

state.

X(1835) is observed in It could be same structure as the ppbar mass threshold enhancement, i.e., it could be a ppbar bound state.

pp

ppJ /pp

pppp

J

mass threshold enhancement was observed in

Evidence of NX(1610) was observed near KΛ mass threshold, suggesting a KΛ bound/resonant state.

Scalar mesons have been studied carefully (via PWA) in J/ψ hadronic and radiative decay at BESII. We need to understand the scalar puzzle.

J/ψ decay is an ideal place to study exotic structures.

Summary (III)

p pKJ /

For other interesting results from BES II:

There are three BES talks in the parallel sessions:

S.S. FANG: Recent results on J/ decays

Z. WANG: Recent results on (2S) decays

J.C. CHEN: Recent results on (3770) and D decays

谢 谢！Thank You!

MARK-III & DM2 Results

Threshold enhancement

pp/J

Claimed inPhys. Rep. 174(1989) 67-227

Too small statistics to draw any conclusion on the threshold enhancement,

e.g., cannot exclude known particles such as (1760)

MARK-III

DM2

ppM

With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:

much weaker than what BES observed !

NO strong dynamical threshold enhancement in cross sections (at LEAR)

pp

pp

pmppM 2)(

|M|2 |M|2BES BES

elasticelasticM ~|| 2 annlabann PM ~|| 2

Both arbitrary normalization Both arbitrary normalization

Final State Interaction ? —— Not favored

1. Theoretical calculation (Zou and Chiang, PRD69 034004 (2003)) shows: The enhancement caused by one-pion-exchange (OPE) FSI is too small to explain the BES structure.

2. The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI !

BES

one-pion-exchange FSI

|M|2 |M|2

Both arbitrary normalization

BES

pmppM 2)(

Both arbitrary normalization

Coulomb interaction

One-pion-exchange FSI may be too simple, however, FSI does not contradict with ppbar bound state interpretation.

Keep in mind:

We need to explain its large BR to ppbar.

Final State Interaction ? —— Not favored

Theoretical calculation might be unreliable, however, according to Watson’s theorem, we can use elastic scattering experiments to check the FSI effect, i.e.,if the BES structure were from FSI, it should be the same as in elastic scattering: But it is NOT ! FSI cannot

explainthe BES structure.

/J

p

p

p p

p pelastic scattering

|M|2 BES

Both arbitrary normalization

elasticelasticM ~|| 2

pmppM 2)(

No matter what are the interpretations for the recent new surprising observations, these discoveries certainly open a new window for understanding the strong interaction and hadron spectroscopy.

We need to have a global picture if there are new forms of hadrons beyond the naïve quark model —— any pentaquark, tetraquark, molecular state or other multiquark states cannot stay alone !

A lot of opportunities for BES III and other experiments working on hadron spectroscopy !!!

Prospects

BCK subtracted PS corrected

BCK subtracted PS corrected

BCK subtracted PS corrected

Photon angular distributions in

For X(1835) signal MC (assuming 0-+)

MC– MCMADE

MC – After Selection

)( J

Photon angular distributions in

For Data – it is not inconsistent with 0-+ -- statistics is too low.

)( J

X(1835) region

X(1835) sideband

Sideband Subtracted &Eff. corrected

f0(980) is observed in f0(980) at KLOE (Background: ISR, FSR and ).

The results support that f0(980) has large coupling with KK.

f0(980) at KLOE

KLOEPreliminary

f0(980) f0(980)

)(M )(M

Background subtracted

ZEUS observed a narrow peak around 1730 MeV in KSKS mode:

Its width is much narrower than BES and others. Spin-parity needed.

How many mesons in this mass range?

f0(1710) (?) at ZEUS

f0(1710) ???

MeV

MeVM201438

71726