New Observations and Multiquark Candidates

at BESII

HongXun Yang(for BES Collaboration)

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

CPS2006

BEIJING, Sept. 16, 2006

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.

World J/ Sample (106)

2001

0

10

20

30

40

50

60

MarkI I I DM2 BES I BES I I

Outline

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

mass threshold enhancement in

mass threshold enhancement in

mass threshold enhancement in J/

New observation of a broad 1- - resonance in J/ K+K- 0

ppppJ /

pKJ /K

p pKJ /

pp

A possible ppbar bound state

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)   

This result cannot be explained by pure FSI effect, since FSI is a universal effect.

FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored.

This indicates that X(1860) has a production property similar to ’ meson.

c.f.:

This narrow threshold enhancement is NOT observed in at CLEOpp )1( S

No enhancement near threshold

CL

JBrSBr

%90@%7.0

)X /(/)X )1((

CL

JBrSBr

%90@%4.0

)' /(/)' )1((

This again disfavors FSI and indicates that X(1860) has a production property similar to ’ meson.

c.f.:

This also indicates X(1860) may have strong coupling to gluons as ’ meson.

This narrow threshold enhancement is NOT observed in at BESIIpp / J

No narrow strong enhancement near threshold

CL

JBrJBr

%95@5.0

)X /(/)X/(

04.0

)' /(/)' /(

JBrJBr

Pure FSI disfavored

I=0 S-wave FSI CANNOT fit the BES data.

ppp mM 2

58/192../2 fod

FSI * PS * eff + bck

FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0)

X(1860) has large BR to ppbar

We (BES) measured:

From Crystal Ball result, we etimate:

So we would have:

(This would be the largest BR to ppbar among all known mesons)

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

3102))1860(/( XJBR

%4))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 !

Summary of the properties of the strong ppbar mass threshold enhancement X(1860)

So far, it is only observed in J/ radiative decays:• It has production properties similar to ’ meson.• It could have strong coupling to gluons as ’ meson.

It could have the largest decay BR to ppbar among all PDG particles:• It has strong coupling to ppbar.

New Observation of X(1835) in

J

PRL 95, 262001 (2005)

Observation of X(1835) in

The +- mass spectrum for decaying into +- and

Statistical Significance 7.7

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

Re-fit to J/p pbar including FSI

Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0)

M = 1830.6 6.7 MeV

< 153 MeV @90%C.L.

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.

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)   

K mass threshold enhancement

)(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.

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. Phys. Rev. C71: 064001, 2005 )

Ecm – ( MΛ+MK ) (MeV)

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

(5-quark system with hidden ssbar components).

Observation of mass threshold enhancement

We studied DOZI process:

J/ + + +-0 K+ K-

Clear and signals

recoiling against

Dalitz Plot

A clear mass threshold enhancement is

observed

Acceptance

Phys. Rev. Lett. 96, 162002 (2006)   

The radiative decay of J/ has been observed in the 58M J/ data.

A significant structure of has been found near the mass threshold.

PWA shows the structure favors 0++, with a mass , width 1052028 MeV, and the corresponding branch ration is (2.610.270.65)x10-4.

It could be a multiquark/hybrid/glueball state.

Its relation with f0(1710),f0(1790)?

MeV181812 1926

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

New observation of a broad 1- - resonance in J/ K+K- 0

hep-ex/0606047, Submitted to Phys. Rev. Lett.

0

J/ K+K- 0

very clean 0 signal

)1580(X

Background

0

)890(*K

)1580(X

)1410(*K

J/ K+K- 0

PID and kinematic fit can significantly reducethe dominant background from J/ + - 0.

Parity conservations in J/ K+K- 0 requires that

spin-parity of K+K- should be 1--,3--,…

PWA fit with and

phase space (PS) gives ( preliminary ):

( can be ruled out by much worse likelihood )

X pole position

big destructive interference among and PS

1PCJ

)1410( ),890( (1700), , ** KKX

232116712

98499155 / )(409 )1576( cMeVi

47.26.3

0 10)6.05.8()()/(

KKXBrXJBr

(1700) , X

3

Partial Wave Analysis of J/ K+K- 0 events

Broad X cannot be fit with known mesons or their interference

It is unlikely to be (1450), because:

• The parameters of the X is incompatible with (1450).

(1450) has very small fraction to KK. From PDG:

It cannot be fit with the interference of (770) , (1900) and (2150):

• The log-likelihood value worsens by 85 (2=170).

.).%95( 106.1))1450(( 3 LCKKBr

How to understand broad X(1580)?

Search of a similar structure in J/ KSK will help to determine its isospin.

X(1580) could have different nature from conventional mesons:

• There are already many 1- - mesons nearby.

• Width is much broader than other mesons.

• Broad width is expected for a multiquark state.

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 very narrow and strong mass threshold enhancement is uniquely observed in decays at BES II:• It is NOT observed in Y(1S) decays, nor in J/psi

hadronic decays. FSI is strongly disfavored.• 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 pp

J

mass threshold enhancement was observed in

Evidence of NX(1610) was observed near KΛ mass

threshold, suggesting a KΛ bound or resonant state.

An mass threshold enhancement was observed in J/ .

A very broad 1- - resonance X(1580) is observed in J/ K+K- 0 .

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

Summary (III)

p pKJ /

谢 谢！Thank You!

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 ）

How quarks/gluons form a hadron is far from being well understood.

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 one of the hottest topics in the hadron spectroscopy.

What do we expect from J/psigamma ppbar results?

The baryonium interpretation of the ppbar mass threshold enhancement predicts a new particle around 1.85 GeV which should be observed in other decay mode with full BW resonant structure.

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

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

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.

Pure FSI disfavored (I)

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

FSI Factors

Most reliable full FSI factors are from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) ， which fit ppbar elastic cross section near threshold quite well.

ppbar elastic cross section near threshold

I=1 S-wave

I=0 S-waveP-wave

pmppM 2)(

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, Phys.Rev.D71:054010, 2005

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

So, pure FSI is strongly disfavored.

However, we do not exclude the contribution from FSI.

pp near threshold enhancement is very likely due to some broad sub-threshold 0-+ resonance(s) plus FSI.

From B.S. Zou, Exotics 05:

From A. Sirbirtsev :

FSI factors should be included in BW fit.

Re-fit to J/p pbar including FSI

Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0)

M = 1830.6 6.7 MeV

= 0 93 MeV

ppp mM 2

FSI * BW * PS * eff + bck

Crystal Ball results on inclusive photon spectrum of J/psi decays

3109.0~)/( JBR

3103.4~)'/( JBR

3103~))1440(/(

50~

JBR

MeV

3102)/(

)18601830(

XJBR

X

Discussion on I=1 S-wave FSI

Pure FSI disfavored (III) — I = 1

Pure I=1 S-wave FSI is disfavored by more than 3 .

ppp mM 2

Pure FSI FSI + BW

M = 1773 21 MeV

= 0 191 MeV

3.85ln2 L 8.65ln2 L

I=0 dominant in J/ radiative decays

Most I = 0 states have been observed in J/ radiative decays with big production rate ( especially for 0-+ mesons ) such as , ’, (1440), (1760), f2(1270), f2(1525), f0

(1500), f0(1710).

The only observed I=1 meson in J/ radiative decays is 0 with low production rate 4*10– 5, e.g., no evidence for (1800) in J/ 3 process.

It is unlikely to be from (1800) .

I=1 S-wave FSI seems unlikely.

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.

0/ J

/J

0/ J

)('/ J

BES II Preliminary

No (1800)

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

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

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

• 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…

Observations of this structure in other decay modes are desirable.

Analysis of )( J

' X(1835)5.1

Analysis of )( J

'X(1835)6.0

Comparison of two decay modes

Mass and width from m=1827.48.1MeV/c2 , =54.234.5MeV/c2

Mass and width from m=1836.37.9MeV/c2 , =70.323.1MeV/c2

)( J

)( J

)( J410)7.08.1()()( XBXJB

)( J410)5.03.2()()( XBXJB

The mass, width and branching fractions obtained from two different decay modes are consistent with each other.

Similar enhancement also observed in pK'

4 away from phase space.

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

Side-bands do not have mass threshold enhancement

Side-bands

Four decay modes are included :

Amplitudes are defined by Covariant tensor formalism B.S. Zhou and D.V. Bugg, Eur. Phys. J. A16, 537(2003)

BW with energy-dependent width

J.H. Kuhn, A. Satamaria, Z. Phys. C48, 445 (1990).

fitPWA :hist

data : points

0*

0*

)1410(

)890(

: 1

KK

KK

component

)1410( ),890(

)(,)(/

),( ,))1700(,(/

***

0**

0

KKKwhere

KKKKJ

KKXXJ

122

22

2

))(

)(()()(

;)(

1)(

l

R

RRRR

RR

Mp

sp

s

MMs

ssiMssBW

PS

KK

KKX

component

)1700(

: 1

Partial Wave Analysis of J/ K+K- 0 events

Angular distributions for events withfrom PWA fit

Figures on the right: (a),(c),(e) are polar angles in lab. reference frame (b),(d),(f) are polar angles in CM frames of respectively

2/ 7.1 cGeVMKK

fitPWA :hist data, : points

KKandK 0

Features of the enhancement near the threshold of mass spectrum at BES II

J/pp

M(pp)-2mp (GeV)

0 0.1 0.2 0.3

pp

BES II Peak position:

~ 0 MeV above threshold

“Width”:

~ 60M eV

Strong (“Height”):

(S+B)/B ~ 2

The above features may help us easily to judgewhether it is observed in other processes.