Recent BESII ResultsRepresenting BESII Collaboration

Weiguo Li

Institute of High Energy Physics,

Beijing 100049, P.R. China

liwg@ihep.ac.cn

NSTAR Workshop

Bonn, Sep. 6, 2006

Outline

Introduction

Light Hadron Spectroscopy from J/ Decays

Study of Excited Baryon States

Selected BF Measurements

Summary

BESII DetectorBESII Detector

VC: xy = 100 m TOF: T = 180 ps counter: r= 3 cm MDC: xy = 250 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.4 % = 7.9 mr B field: 0.4 T p/p=1.8(1+p2) z = 2.3 cm Dead time/event: 〈 10 ms

Data from BESII

Ecm (GeV)

Physics BESII Data

2-5 R scan

2. 2. 2.2,2.6,3.0

R value,

QED, (g-2)

QCD

6+85 points

3.1 3.69 3.78

J/ (2S) (3770)

5.8107

1.46107

~27 pb-1

BESII finished data taking April 2004

Scalars: , clearly observed

X(1835) in J/ ’

The threshold enhancement in J/

New observation of a broad 1- - resonance in J/

K+K- 0

(1760) in J/

Light Hadron Spectroscopy from J/ Decays

The pole in at BESII

/J

M()

M(+-0)

M(+-

)

0

Averaged pole position: (541 39) (252 42)i MeV

Phys. Lett. B 598 (2004) 149

κ

24877

8173 MeV/c )45309()30841(

i

Phys. Lett. B 633 (2006) 681

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

PRL 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/pp 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-+ pp Bound State

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

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

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

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.

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)

J/ pp

Clear signal is seen,

B(J/ pp) =( 9.8 0.3 1.4 ) 10–4

B(J/ X(1860))B(X(1860) pp) < 1.5 10–5 @ 95% C.L.

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

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

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

04.0

)' /(/)' /(

JBrJBr

Summary of new studies on pp 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?

We studied DOZI process:J/ + + +-0 K+ K-

recoiling against

mass threshold enhancement

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

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++, M = ,

=1052028 MeV, and the corresponding branch

fraction = (2.610.270.65)x10-4.

It could be a multiquark/hybrid/glueball state.

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

MeV181812 1926

New observation of a broad 1– resonance

in J/ K+K- 0

0

background 0 sideband

?

K*(892)

K*(1410)

X(1580)

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

Phys. Rev. Lett. 97 (2006) 142002

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

Phys. Rev. Lett. 97 (2006) 142002

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 multi-quark state.

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 masses)

signal with multiple entries

0 ,/ J

Phys. Rev. D 73 (2006) 112007

0-+ Meson

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

Study of Excited Baryon States

Motivation

Probe the internal structure of light quark baryons

Search for missing baryons predicted by quark mod

el

Obtain a better understanding of the strong interacti

on force in the non-perturbative regime

Experimental Advantages

processes branching ratios(10-

3)N* decays

2.00.1

6.00.5

2.00.1

2.10.2

0.90.4

1.30.3

0/ ppJ ppJ /

relatively large branching ratios

npJ / ppJ /

'/ ppJ ppJ /

NN *

NN *NN *

NN *NN '* NN *

58 M J/ and 14 M (2S) at BES II

Pure isospin 1/2

Feynman diagram of the production

of

For and ,

and systems are limited to be pure isospin 1/2.

**,*,*, Np

NNJ / NNJ / N

N

N* in .

Phys. Rev. Lett. 97, 062001 (2006)

npπJ/ψ

N* in +c.c.

L=0 limits it to be

3/2+ or 1/2+

npπJ/ψ

N*(1440)

N*(1520)

N*(1535)

N*(1650)

N*(1675)

N*(1680)

?

npπJ/ψ nπpJ/ψ

About 10 K events are selected N*(1440) is observed directly in the mass spec

trum Possible new N* resonance

L=0 limits it to be 3/2+ or 1/2+ Detailed information need PWA

N* in +c.c.

221540- MeV/c 4014165 ,MeV/c 3 2068 M

npπJ/ψ

(2S) p . .n c c

Phys. Rev. D74, 012004 (2006)

Large accumulation below 1.5 GeV/c2 ，

which may be due to N(1440), N(1520),N(1535) etc.The cluster above 2 GeV/c2 is partlydue to the reflection of N(1440) etc.,and partly may due to high mass N*.No clear N(2065) peak, but we can notrule out its existence.

N* in . 0ppJ/

M

0

)p(M 02

M2(p0

)

N* in . 0ppJ/

0pM

0p

M

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

N* in . 0ppJ/

data

Fit results

Fit results agree with data reasonably, especially in the low mass region.

N* in . 0ppJ/

Optimized masses and widths,

other resonances are fixed.

N* in . 0ppJ/

More than 10 K events were selected, and detailed PWA was performedN(2065) is needed in the fit, and JPC favor 3/2+

Only N(1710) is needed in the M = 1.7 GeV regionThe masses and widths of some other N* have also been given

3 2 2-4M 2040 25 MeV/c , 230 8 56 MeV/c

0(2S) pp ( )

A faint accumulation of events around 2065 MeV/c2

The enhancement between 1.4 and 1.7 GeV/c2

Possible N*(1535) in the p invariant mass

Phys. Rev. D71, 072006 (2005)

0

-J/ψ pK Λ+c.c.

-J/ψ pK Λ+c.c.

Phys. Rev. Lett. 93, 112002 (2004)   

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

-J/ψ pK Λ+c.c.

Two clear peaks at 1520, 1690 MeV/c2 in pK mass N* in K mass PWA is being performed

N*(1535)?

N*(1650)?*(1520) *(1690)

pKM KM

PS, eff. corrected(Arbitrary normalization)

MMM KΛK

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.

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

0SnKJ/

KS

A enhancement near S threshold is evident

N* and * found in the S and nS spectrum

0SnKJ/

N* *

tested.rule" "12%

observed.symmetry SU(3) sample. data 2larger

a with BR remeasure BESI,by t measuremenFirst

S

)c/GeV(m 2

p

00

)c/GeV(m 2

p

)c/GeV(m 2

p

x 10-4 x 10-4

Angular distribution:2

Baryonic decays

Rich structure (N*s), statistics (~850 evts in each mode). Still low for a partial wave analysis.

PRD74, 012004 (2006)

2006 062001, PRL97,

obtained events 000,100

../ ccnpJ

27.091.1:27.086.1:1)'(:)'(:)'( 0 npBnpBppB

Test I-spin symmetry(prediction: 1:2:2)

’(J/) +0/ Is it really B(0)>B()?

arXiv: 0707.1127 [hep-ex]Submitted to PRD

First measurement!

background fromJ/ ΣΛπ

signal

J/ with 0p, p +

Clear is seen,

B(J / + c.c. ) = 1.52±0.08±0.16)10-3

BEPC II

Energy range 1 – 2.1 GeV

Optimum energy 1.89 GeV

Luminosity 1 x 10 33 cm-2s-1 @ 1.89 GeV

Injection Full energy injection: 1.55 1.89 GeV Positron injection speed > 50 mA/min

Synchrotron mode 250 mA @ 2.5 GeV

Upgrade of BEPCDouble-ring collider, 93 bunchesHigh luminosity

Design Goal

Magnet: 1 T Super conducting

MDC: small cell & He gas xy=130 m p/p = 0.5% @1GeV dE/dx=6%

TOF: T = 100 ps Barrel 110 ps Endcap

Muon ID: 9 layer RPC

EMCAL: CsI crystal E/E = 2.5% @1 GeV z = 0.6 cm/E

Trigger: Tracks & ShowersPipelined; Latency = 6.4 s

Data Acquisition: Event rate = 3 kHz Thruput ~ 50 MB/s

BESIII Detector

The detector is hermetic for neutral and charged particle with excellent resolution , PID adequate, and large coverage.

Resonance Energy(GeV)

Peak Lum.(1033cm-2s-1)

Physics Cross Section (nb)

Nevents/yr

J/ 3.097 0.6 3400 10 109

3.670 1.0 2.4 12 106

(2S) 3.686 1.0 640 3.2 109

D0D0bar 3.770 1.0 3.6 18 106

D+D- 3.770 1.0 2.8 14 106

DsDs 4.030 0.6 0.32 1.0 106

DsDs 4.140 0.6 0.67 2.0 106

Average Lum: L = 0.5×Peak Lum.; data taking time: T = 107s/year

Yearly Event Production

Huge J/ and (2S) samples at BESIII

Two rings are commissioned with normal quadrupole magnets,

with 100 mA in each beam of 20 bunches, with a luminosity clos

e to 1031 .

Two periods providing synchrotron Radiation users with a m

ax. current of 180 mA at 2.5 GeV.

SCQ and Detector SC magnet have been tested and fields wer

e measured.

Most detectors are assembled, will be fully assembled end of 2

007, and cosmic ray for 2 months, to the beam line end of March

2008.

Commissioning machine/detector together next summer.

Some test runs, luminosity to reach 31032 end of 2008 .

Summary

New states are observed in the hadron spectroscopy:

, , X(1835) in J/ ’, X(1580) in J/ KK, enhancement in J/ , (1760) in J/ ;

Excited baryons, N* observed in J/ pn ; J/ pp0 ; J/ nKS; Compared with (2S) decay;

Some N*, as N*(1535), N*(2065) better measured.

Some BF involving baryons are measured;

BEPCII/BESIII should collect data in 2008.

Thanks

0

5

10

15

20

25

30

MKI MKII MKIII CBAL BESI BESII CLEO CLEOc

(2s) data samples’ decays

Leptonic decays

Radiative decays

Hadronic decays

cJ decays

VV

PPP

3M

14M

4M

outline

26M

Also 6.42 pb-1 of data at Ecm=3.65 GeV for background study.

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