Recent BESII Results and Future Prospects

Zhipeng ZHENG

Representing BES Collaboration

Institute of High Energy Physics, CAS

Outline

Introduction

New observations at BESII

Study of the scalars

BESIII/BEPCII project

Beijing Electron Positron Collider (BEPC)

L ~ 51030 /cm2s at J/ Ebeam~ 1 – 2.5 GeV

BESI started running in 1989BESII started running in 1997BESIII will start running in 2008

0

10

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30

40

50

60

CBA L MK II MK III DM2 BES I BES II

BESII Detector

VC: xy = 100 m TOF: T = 180 psMDC: xy = 220 m BSC: E/E= 21 % dE/dx= 8.5 % = 7.9 mr p/p=1.78(1+p2) z = 2.3 cm counter: r= 3 cm B field: 0.4 T z = 5.5 cm

0

5

10

15

20

25

30

MKI MKII MKIII CBAL BESI BESII CLEOc

J/

(2S)

World J/ and (2S) Samples (×106)

BESII 58M J/

BESII 14M (2S)

BEPC / BESBEPC / BES

mass measurementR measurementNew states in J/→pp … Candidates for Glueball

J/， ’， D and Ds physics …￣ ￣

Tau mass measurement, （ 1991 － 1992 ）

World average (1991) BES result:

MeVm 7.26.31.1784

MeVm 30.027.096.1776

025.0941.0

g

g 0069.00005.1

g

g

Universality for lepton is stand up

tau mass fit

－ universality comparation from 1992 to 1996

BEPC/BES R measurement

New observations at BESII

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 0.33-body phase space

acceptance

2/dof=56/56

acceptance weighted BW +3 +5

10 25

pp

BES II

Phys. Rev. Lett. 91, 022001 (2003)   

X(1860)

X(1860) has large BR to pp

BES measured:

From Crystal Ball result, we estimate:

So we would have:

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

3102))1860(/( XJBR

%4))1860(( ppXBR

Considering that decaying into pp 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 pp !

B+ pp K+ at BaBar and Belle

BaBar

210 fb-1

Belle

BES II

ppJ / The pp threshold enhancement observed in J/ decay is different from the enhancements observed by Belle and BaBar in B decay.

The one in B decay can be explained by fragmentation.

X(1860)

KppB

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

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

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

No enhancement near threshold

CL

JBrSBr

%90@%7.0

)X /(/)X )1((

PRD73, 032001(2006)

This again disfavors FSI’

This narrow threshold enhancement is NOT observed in at BESII

No narrow strong enhancement near threshold

CL

JBrJBr

%95@5.0

)X /(/)X/(

BESII Preliminary

ppJ /

Observations of this structure in other decay modes are desirable.

Search for the strong mass threshold enhancement X(1860) in

A strong mass threshold enhancement was observed in

• No obvious strong mass threshold enhancement was observed in

acceptance

X(1860)

Fit

CL

ppXSB

%90@104.5

))1860()2((6

pp

pp pp

ppS )2(

ppS )2(ppJ /

M(pp)-2mp (GeV)

0 0.1 0.2 0.3

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

+3 +510 25

5107~

))1860(/(

ppXJB

acceptance

BESII preliminary

Statistical Significance 7.7

X(1835)7.7

2

2

MeV/c 7.73.207.67

MeV/c 7.21.67.1833

54264

M

Nobs

410)4.04.02.2()()( XBXJB

PRL 95 (2005) 262001

BES: X(1835) in '/J

M = 1830.6 6.7 MeV

= 0 93 MeV

In good agreement with X(1835)

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

Fit to J/ pp including FSI

BES II Preliminary

I=0

I=1

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

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

’ mode is expected to be the favorable decay mode for a pp bound state below pp mass threshold

G.J. Ding and M.L. Yan, hep-ph/0502127

Observation of p mass threshold enhancement in

J/pK-

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* 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.

Observation of thresholdenhancement in J/

) ,( 0 KK

OZI DOZI KKJ ,/ /J

M(+-0)

M(K

+K-

)

M(K+K-)

MeVMMKK

15||

MeVMMMeVKK

35||20

M(+-0)

Dalitz plot

Clear and signals

M2()

M2 (

)

A clear threshold enhancement is

observed

Eff. curve

Phase Space

Side-bands

Side-bands do not have mass threshold enhancement!

PWA shows: the enhancement favors 0++ over 0-+ and 2++

.

Is it the same 0++ observed in KK or (f0(1710), or f0

(1790)), or is it a glueball, or a hybrid …..?

2

21926

MeV/c 2820105

MeV/c 181812

M

Further look in , K*K*, …. is desirable !

410)65.027.061.2()()/( XBrXJBr

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

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

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.

What is the broad resonance? JPC should be 1--, 3--, …(Parity conservation)

PWA results Following components are needed

K*(892), K*(1410), (1700), X

1– is much better than 3—

Pole position of X is

Br

Big destructive interference among X, (1700) and PS 47.2

6.3-0 10)6.05.8( )KKX ,Xπ(J/ψ

232 1167 12

98 4991 55 MeV/c )409()1576(

i

1-- component

Study of the scalars

There have been hot debates on the existence of and .

Lattice QCD predicts the 0++ scalar glueball mass in the range 1.5 - 1.7 GeV.

f0(1500) and f0(1710) are good candidates.

study in

study in

study f0(980), f0(1370), f0(1500), f0(1710) and f0(1790) in

/' ,/ JJ

KKKKJ and / *

, / KKJ ，，

0++

The study of evidence for a low mass pole in the early D

M2 and BESI data on J/ .

huge event concentration in the I=0 S-wave channel seen in M ~ 500 – 600 MeV in the pp central production exp.

to explain scattering phase shift data ， should be introduced in chiral perturbative theory.

FNAL E761 exp. D+ +-+ dataMeV 21324 MeV, 17478 42

402423

M

The pole in at BESII /J

M(+-)

BES, PLB 598 (2004) 149

MeV )42252()39541( i

Different parameterizations of BW are used in PWA.

Averaged pole:

observation of in ’+-J/ Measure the universal pole position (552 - i232 MeV) World largest signal (with ~ 40,000 tagged events)

Phys. Lett. B 645 (2007) 19

The study of A possible pole is controversial. Some analyses of LASS K scattering data need (800), some don’t.

Scadron et al. favors a nonet made up of , (800), f0(980) and a0(980).

Julich group used t-channel exchanges to explain K scattering data.

evidence of in FNAL E791 data on D+ K-++

slightly lower statistics of CLEO D0 K-+0 data find no evidence of

FOCUS data on K+K-++ require K*0 interfere with either a constant amplitude or a broad 0+ resonance in K

MeV 8743410 MeV, 4319797 M

PWA result:

is needed in the fit.

Pole position of :

BES observed in J/K*KKK

BES II58 M J/

24872

8173 MeV/c )45309()30841(

i

Phys. Lett. B 633 (2006) 681

A possible pole is controversial.

Lattice QCD:

the lightest scalar glueball in the region of 1.5- 1.7 GeV

Glueball searches should be performed in simultaneously.XXXJ ,,/

Study of other scalars

0++ states: f0(980), f0(1370), f0(1500), f0(1710), f0(1790)

PDG 2006 values:

f0(980): M = 980 10 MeV, = 40 – 100 MeV

, KK

f0(1370): M = 1200 – 1500 MeV, = 200 – 500 MeV

2, 4, KK …

f0(1500): M = 1507 5 MeV, = 109 7 MeV

2, 4, , ’, KK …

f0(1710): M = 1714 5 MeV, = 140 10 MeV

2, 2K, 4, , ’ …

Important parameters from PWA fit:

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

/J

KKJ /

f0(980)

21.025.021.4

1510165

68965

g

g

MeVg

MeVM

KK

ss

f0(980)

f0(980)

Phys. Lett. B 607 (2005) 243

There has been debate whether f0(1370) exists 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)

MeV

MeVM

40265

501350

Phys. Lett. B 607 (2005) 243

Clear f0(1710) peak in J/ KK.

No f0(1710) observed in J/ !

f0(1710)

KKJ /

/J

f0(1710)

NO f0(1710)

MeV

MeVM

20125

301740

CLKKfBR

fBR%95@13.0

))1710((

))1710((

0

0

Phys. Lett. B 603 (2004) 138

KKJ /

00/ ss KKJ

)1710(0f

)1710(0f

MeV 166

MeV 41740155108

1025

M

PWA analysis shows one scalar in 1.7 GeV region

Phys. Rev. D 68 (2003) 052003

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)??

/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 ??

Scalars in J/

Two scalars in J/ :

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

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

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

00/ J

Phys. Lett. B 642 (2006) 441

OZI rule and flavor tagging in J/ hadronic decays

In J/ hadronic decays, an or 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

dduu

dduu

ss

ss

Future Prospects

BESIII/BEPCII project.

Government approved. Started construction from the end of 2003.

BEPCII: a high luminosity double–ring collider

SC RF

Two rings tunnel

BEPCII Design goal

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

Dual purpose machine

May achieve to Ebeam = 2.3 GeV

BESIII Detector

Be beam pipe

SC magnet Muon Counter

Drift Chamber

CsI(Tl) calorimeter

TOF

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 Two rings, 93 bunches:

• Luminosity

1033 cm s @1.89GeV

6 1032 cm s @1.55GeV

6 1032 cm s @ 2.1GeV

MDCParametersR inner: 63mm ; R outer: 810mm Length (out.): 2582 mm Inner cylinder: 1.2 mm Carbon fiberOuter cylinder: 11.5 mm CF with 8 windowsSense wire : 25 micron gold-plated tungsten (plus 3%Rhenium ) ---

6796 Layers (Sense wire ): 43

Expected performance

Field wire: 110 micron gold-plated Aluminum --- 21884Gas: He + C3H8 (60/40)Cell: inner chamber --- 6 mm

outer chamber --- 8.1 mm

%6~

@1GeV/C%5.0~

130~

dxdE

P

m

dx

dE

P

x

Wire Stringing Completed, bad wires are replaced, glue used to make gas tight

CsI(Tl) crystal calorimeter Design goals:

Energy: 2.5% @ 1GeV Spatial: 0.6cm @ 1GeV

Crystals: Barrel: 5280 w: 21564 kg Endcaps: 960 w: 4051 kg Total: 6240 w: 25.6 T

France

Sanit -Gobain

Shanghai Institute of Ceramics

Beijing

Hamamatsu

Total

Ordered 2040(960) 1920 1320 5280(960)

Arrived 2023(824) 1920 1320 5263(824)

Rejected

87 322 79 488

Mechanical structure

A 1/60 prototype

Status: Assembly will start soon.

Should be completed early next year.

By the end of the year, all FED boards should be tested and installed.

晶体支撑架和工装架

All RPC production, assembly, testing, and installation completed.

BEPCII Status and Plan

Dec. 2006, ring commissioning, beam accumulation, Synchrotron run.

Dec. 07, BESIII moved to the beam line. 2008, Commissioning ring and detector together, test ru

n. Dec. 08, to achieve a lum. of 31032cm-2s-1.

BESIII Collaboration

Institute of High Energy PhysicsUniversity of Science and Technol

ogy Peking University Tsinghua University Shangdong University Nankai University Central China Normal University University of Anhui University of Zhejiang University of Zhengzhou Nanjing Normal University Nanjing University Shanxi University Sichuan University Henan Normal University

University of Hawaii University of Washington University of Tokyo Joint Institute of Nuclear R

esearch, Dubna GSI University of Bochum University of Giessen

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

Nevent/year = exp L T

Yearly Event Production

Huge J/ and (2S) samples at BESIII

J/ Physics at BESIII/BEPCII

Search for glueballs, hybrids and multi-quark states

Systematic study of light hadron spectroscopy

Study of the excited baryon states Search for more J/ decay channels Probing for new physics in J/ decays c physics

New states : X(1860), X(1835), X(2075), X(1812), X(1580) were observed

and studies

Other scalars

BESIII/BEPCII will start taking data in 2008.

Summary Summary