New Results and Prospectsof Light Hadron Spectroscopy

Shan JINInstitute of High Energy Physics (IHEP)

jins@mail.ihep.ac.cnPresented by Yi-Fang Wang

Charm 2007

Ithaca, August 7, 2007

Outline

New results on 0-+ mesons

New results on 0++ mesons

New results on 1-- mesons

New results on baryons at BESII

Prospects of glueball searches at BESIII

New results on 0-+ mesons

(1760) in at BESII /J

M(+-0)(GeV/c2) M(+-0)(GeV/c2) M(+-0)(GeV/c2)

M(

+-0

)(G

eV/c

2 )

sideband

signal after best candidate selection (best w masses)

signal with multiple entries

0 ,/ J

Phys. Rev. D 73 (2006) 112007

Eff. curve

Phase Space Side-bandM() M()

(1760) f0(1710)f0(1790)f0(1810)

PWA analysis

M()

Total

f2(1910) f2(160) BGUsing observed mass and width for f0(1810)in J/

f0(1710)

f2(1910)

f2(1640)

BG

(1760) > 10

f0

M() (GeV/c2)

The existence of (1760) is confirmed Its mass and width were first correctly measured with PWA.

3-

22421

2

100.32)0.08(1.98

))1760(())1760(/(

MeV/c 25244

MeV/c 15101744

BrJBr

M

Phys. Rev. D 73 (2006) 112007

Candidate of 0-+ baryonium

Observation of X(1835) in at BESII

The +- mass spectrum for decaying into +- and

Statistical Significance 7.7

J

J

54264obsN

MeVm 7.21.67.1833

MeV7.73.207.67

Phys. Rev. Lett. 95, 262001 (2005)   

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)   

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)

Candidate of 0-+ ppbar Bound State

X(1835) could be the same structure as ppbar mass threshold enhancement X(1860)/X(1830).

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.

There is already an (1760) nearby , so that X(1835) is very likely to be an unconventional 0-+ meson.

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

No enhancement near threshold

CL

JBrSBr

%90@%7.0

)X /(/)X )1((

)(%90@%4.0

)' /(/)' )1((

PDGCL

JBrSBr

Phys.Rev.D73, 032001(2006)

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

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

c.f.:

No strong threshold enhancement is observed in at BESIIpp '

No significant narrow strong enhancement near threshold(2.0 if fitted with X(1860))

..%90@%8

)X /(/)X '(

LC

JBrBr

%4~3

)' /(/)' '(

JBrBr

Phys.Rev.Lett.99, 011802 (2007)

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 strong 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

BESII Preliminary

Summary of new studies on ppbar mass threshold structure X(1860)

Pure FSI effect cannot explain X(1860) structure.

X(1860) has production properties similar to ’ meson • Why a baryonium (candidate) has a production prop

erties similar to ’ meson? ’ excitation? Why an ’ excitation dominantly deca

ys into ppbar above ppbar mass threshold?

New results on 0++ mesons

Observation of mass threshold enhancement at BESII

Phys. Rev. Lett. 96,162002 (2006)

We studied DOZI process:

J/ + + +-0 K+ K-

recoiling against

A clear mass threshold enhancement is

observed

Acceptance

Side-bands

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

PWA of J/ +- and 00 at BESII

Phys. Lett. B 642 (2006) 441

/J?)1500(0f ?)1710(0f

00/ J

PWA of J/ +- and 00

M(+- )

M(00 )

The channels fitted in PWA:

)1500(0f )2020(0f?)1710(0f

)1270(2f )1810(2f )2150(2f

)2050(4f all 0++ all 2++

PWA components:

PWA results

Lower 0++ : 0++ is strongly preferred over 2+

+

f0(1370) cannot be excluded.

Higher 0++: f0(1710) or f0(1790)

MeV ) 21108(

MeV )1661466(1411

M

MeV ) 238145(

MeV )111765( 43

M

/J

00/ J

Phys. Lett. B 642 (2006) 441

About f0(1500) It is first clearly observed in J/psi radiative decays. Its production rate in J/psi radiative decays:

)(

101~))1500(())1500(/( 400

BESII

fBRfJBR

0( (1500) ) ~ 35%( )BR f PDG

40 103~))1500(/( fJBR

The production rate of f0(1500) in J/psi radiative decays is

lower than f0(1710):4

0( / (1710)) 9 10 ( )BR J f PDG

It indicates f0(1710) has stronger coupling to gluons than

f0(1500) which one contains more glueball content?

New results on 1-- mesons

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

Phys. Rev. Lett. 97 (2006) 142002

J/ K+K-0

0

background 0 sideband

?

K*(892)

K*(1410)

X(1580)

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

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

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:

( 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.

A structure at 2175MeV was observed in e+e-

f0(980), via initial-state radiation at BABAR.

MeV

MeVm

201658

15102175

Evidence of a new 1-- resonance Y(2175) at BaBar

Phys. Rev. D 74 (2006) 091103(R)

What is Y(2175)?

A conventional state? An analog of Y(4260) ( )? An 4-quark state? More experimental information needed, esp

ecially we can search for it in J/psi decays at BESII and BESIII.

ss

ssssgssss

New results on baryons at BESII

N* in . at BESII0ppJ/

M

0

)p(M 02

M2(p0

)

N* in . 0ppJ/ Resonances used in the PWA

The best results to now

N* in . 0ppJ/

data

Fit results

The comparison between data and PWA fit results.Fit results agree with data reasonably, especially in the low mass region.

N* in . 0ppJ/

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.

Nx* is N(1535)?

From:

If Nx* is N(1535), we would have

Then N(1535) would have very large ssbar component (a 5-quark system).

4102~1~)1535())1535(/( pNBRpNJBR

10~2

2

p

K

g

g

4** 102~)()/( KNBRpNJBR XX

Such a big coupling to K of N(1535) is NOT observed in process

at SAPHIR

Kp

pKJ

BES

/Phase Space shape

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.

Whether NX(1610) is N(1535) needs further study.

No obvious N* in Dalitz plot.

We measured:

Study of at BESII ppJ/

310)18.003.000.1(

)ppBR(J/

Prospects of glueball searches at BESIII

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.

One Important Physics Goal of BESIII

With 1010 J/psi events, we hope to answer: Whether glueballs exist or not?

• Naively, we estimate in each exclusive decay mode:

• If the eff. is about 20%, we would have 20000 events for each decay mode

we should observe a relative narrow (width: 50~200MeV) glueball if it exists.

510~)()/( hhGBRGJBR

310 210

About scalar glueball Many scalar mesons in the mass range 1.4~1.8

GeV, where a scalar glueball is predicted to be. More studies will be performed at BESIII.

More theoretical studies are also needed:• Not only glueball mass, but also width• Decay patterns• Production rate in J/psi radiative decays• Mixing mechanism

2++ glueball candidates

Lattice QCD predicts the 2++ glueball mass in the range of 2.2~2.4 GeV

(2230) was a candidate of 2++ glueball:• It was first observed at MARKIII in J/KK• It was observed at BES I in J/KK, , ppbar• It was not observed at DM2.

BES-I (2230) Result

(2230)

The situation at BESII

The mass plots shows no evident (2230) peaks in J/KK, , ppbar, which is different from BESI.

However, it is difficult to exclude its existence since we may still need a small signal at the 4.5 level in the PWA based on our preliminary study. Its mass, width and BR are consistent with BESI and MARKIII results

Difficult to draw firm conclusion at present. We hope to give a final answer at BESIII on (2230)

00/ ss KKJ

KKJ /

Other 2++ glueball candidates

No other obvious good candidates have been observed in J/psi radiative decays in the mass range predicted by LQCD.

What does it mean:• LQCD prediction might not be very reliable, or• BR(J/ G)xBR(Ghh) is small ( <10-4 ) so that we

don’t have the sensitivity to observe it ( quite possible ), or,

• The width of a glueball is very large ( ~1GeV, E.Klepmt ).

Where to search for the 0-+ glueball?

Lattice QCD predicts the 0-+ glueball mass in the range of 2.3~2.6 GeV.

(1440) and X(1835) were suggested being possible candidates, but their masses are much lower than LQCD predictions.

No 0-+ glueball candidate observed in the mass range 2.3~2.6 GeV

No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in

Again:• LQCD reliable?• Production rate could be v

ery low.• Glueball width could be ve

ry large.

...',

*,*,,/

KKKKJ

'M

)1835(X

Summary

New results on light 0-+,0++ and 1-- mesons as well as excited baryons were briefly reviewed.

We would expect more new observations on light hadron spectroscopy at BESIII and we hope to answer whether glueballs exist or not at that time.

谢 谢！Thank You!

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