1. BES and BEPC: Status and Prospects
Zhengguo ZHAO IHEP of CAS, Beijing
I Current Status
II Recent Results
III Future Plans
IV Summary
Workshop on Prospects for CLEO/CESR with 3<Ecm<5 GeV, Cornell University
May 5-7, 2001

2. The BES Collaboration Korea (3) Korea Univ. Seoul National Univ.
Chonbuk National Univ.
Japan (4)
Nikow University
Tokyo Institute of Technology
Miyazaki Univ.
KEK
USA (4)
University of Hawaii
University of Texas at Dallas
Colorado State University
Stanford Liner Accelerator Center
UK (1)
Queen Mary Univ.
China (14)
IHEP of CAS, CCAST
Univ. of Sci. and Tech. of China
Shan Dong Univ. , Nan Kai Univ.
Peiking Univ., Shanghai Jiaotong Univ.
Zhe Jiang Univ., Wu Han Univ.
Hua Zhong Normal Univ.
Henan Normal Univ.,
Hunan Univ., Liaoning Univ.
Tsinghua and Sichuan Univ.
are going to join
The BES Collaboration

3. The Beijing Electron Positron Collider
A unique e+e- machine operating in 2-5 GeV since 1989
L ~ 51030 /cm2s at J/ peak, single bunch

4. Daily J/y operation of BEPC
Period Days Beam time (hrs.) J/y events Lmax(1030cm-2 s-1) t(hrs)
M ~
M ~ 10 20 30 40 50 60
500
1000
1500
Beam Current (mA)
Time (min)

5. BEPC Beam Time Distribution
Unit: month
HEP SR
BEPC
Summer maintenance 5 3
1.5-2
2.5-2

6. BESII Detector(upgraded from 1995-1997)
VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm
MDC: xy = m BSC: E/E= 22 % z = 5.5 cm
dE/dx= 8.4 %  = 7.9 mr B field: T
p/p=1.8(1+p2) z = 2.3 cm Dead time/event: 10 ms

7. Recent Results from BES
R Scan in 2-5 GeV
Charmonium physics
- Results from J/ data
- Results from (2S) data

8. Definition of R R: one of the most fundamental
quantities in particle physics
Experimentally
Nhad: observed hadronic events
Nbg: background events
L: integrated luminosity
had: detection efficiency for Nhad
: radiative correction

9. Relative Contributions to the Uncertainties of a and (MZ2)

10. BES R Scan in 2-5 GeV March-May, 1998: 6 energy points
at 2.6, 3.2, 3.4, 3.55, 4.6, 5.0 GeV
Feb.- June, 1999:
85 energy points at GeV
+ 24 points separated beam operation
+ 7 points single beam operation for both e+ and e-

11. Some Values at a Few Typical Energy Points to Determine R
Ecm(GeV)
Nhad
N+N
L(nb-1)
had(%)
1+
2.0
1155.4
19.5
47.3
49.50
1.024
3.0
2055.4
24.3
135.9
67.55
1.038
4.0
768.7
58.0
48.9
80.34
1.055
4.8
1215.3
93.6
84.4
86.79
1.113
Systematic Errors (in %) at a Few Typical Energy Points
Ecm(GeV)
Nhad
 triiger
L(nb-1)
 had
(1+)
Total
2.0
7.07
0.5
2.81
2.62
1.06
8.13
3.0
3.30
2.30
2.66
1.32
5.02
4.0
2.64
2.43
2.25
1.82
4.64
4.8
3.58
1.74
3.05
1.02
5.14

12. R Values in 2-5 GeV
3770
4040
4160
4415

13. Experimental R-value Below 5 GeV and QCD Calculation
QCD calculation (M. Davier et al.) in GeV agree well with our data

14. R Values Below 10 GeV

15. The Impact of BES’s New R Values on the SM Fit
170
210 68 90

16. Still larger contribution (BESIII, CLEOC)
CMD,SND
KROE, PEP-N
CLEOC

17. Other Topics With R Scan Data
Pion form factor measurement
Measurement of (e+e-p p-bar)
Events shape of the hadronic events
Measurement of the (2S), (3770) resonance parameters
Structures in GeV energy region

18. Measurement of (3770) Resonance Parameters
Online fast analysis
(2S)
J/
(3770)

19. R Measurement in 2-5 GeV-How to Further Improve?
Large Nhad sample  machine with L~1031 cm-2s-1 for all points
Detector: larger coverage, good performance
Radiative correction should be done better than 1%
Generator LUARLW need to be further improved and huge Nhad event sample is required to tune the parameters
Better handling of background, particularly beam associated ones
Measure exclusive channels  needs high L machine
L ~ 1032 cm-2s-1 and good detector PID
Making use of ISR effect ?

20. Preliminary Results from Charmonium Decays
With J/ data sample, BES has been
Searching for glueball, hybrid and exotic states
Studying of light hadron spectroscopy and excited baryonic states
Searching for LFV and rare decays
Recent preliminary results
Study of the structure around 1.7 GeV mass region
PWA analysis of J/+-, K+K-
Search for Chiral partner  from J/+-
Study of excited baryonic states (N*, *…)

21. J/K+K- (BESII 24 M J/)
J/ f0( ) 
f0(1500)
f0(1710)
f2(1270)
f2’(1525)
f2’(1525): M=1530 (5) MeV, =80 (10) MeV
f0(1710): M=1735 (30) MeV, =180 (20) MeV
0++ is dominant in 1.7 GeV region

22. J/ +- (BESII 24 M J/)
The main contribution in 1.7 GeV
mass region comes from 0++

23. PWA of J/+- (BESII 24 M J/)
A strong f0(980)+- peaked at 98010 MeV
A 0++ signal with M=133530 MeV, =102 13 MeV
A 0++ at M=177020 MeV with =130 40 MeV

24. PWA of J/ K+K- (BESII 24 M J/)
A tail of f0(980) around 1 GeV, a strong component of f2’(1525)
A 0++ component on the shoulder of f2’(1525) might be mainly comes from the misidentifying of K

25. Search for  from J/+-
 S-wave scattering experiment requires 
Linear  model predicts:
M = 2 Mg ~ MeV ~ 400 – 800 MeV
The existence of  as a resonance has not been generally accepted
DM2, MARKIII and BES all found a broad structure in J/+-

26.  Indication of A 0++ : M=390 +60-36 MeV, =282+77-50 MeV
A strong component f2(1270): M= MeV, = MeV

27. (2S) Physics (only BESI data)
(2S) is an important laboratory to study
- charmonium family members
- non-relativistic perturbative QCD
e.g. test of “15% rule” from non-relativistic perturbative QCD
BES has measured many decay channels - many for the first
time, many filled up the PDG and improve the precision

28. Test of “15% Rule”

29. Future Plans Take data with BESII to 2003
- (2S) or (3770) or R in 2-3 GeV?
BESIII at BEPCII
BESIII/BEPCII is the future of the BES
Two options
- multi-bunch single ring: L=31032 cm-2s-1
- multi-bunch double ring: L=1033 cm-2s-1

30. Single-Ring and Double-Ring Schemes
ips
ipn
inj_e + -
vspe
vspw
spne
spnw
spse
spsw
K1_e
K3_e
Parasitic
Collision
-30
-20
-10 10 20 30 40 50 60

31. Design Goals and Main Parameters

32. From BESII to BESIII

33. BESIII New barrel e.m. calorimeter (BEMC)
Scintillating fiber+Pb, E/E~7%
Openable endcaps(door only in the first step)
Drift chamber using Al field wires and He based gas
New trigger and DAQ system adapting multi-bunch train
All corresponding electronics
New luminosity monitor (L.M.)
New barrel time-of-flight (TOF)
Double layer plastic scintillator or MRPC, T~100 ps
New vertex chamber (VC)
New  counter ?
Computing and BESIII software (PC farm, C++, detector simulation based on GEANT3)

34. ? An other idea is to build a complete new
detector using super conducting magnets
+double ring  BTCF
Seems hard to be accepted due to the
limitation of the proposed and endorsed
budget

35. Physics Features in BEPC Energy Region
Rich of resonances, charmonium and charmed mesons
Threshold characteristics
Transition between smooth and resonances, perturbative and
non-perturbative QCD
Energy location of the gluonic matter and glueball, exotic states and hybrid

36. Physics Program Meson spectroscopy with J/, (2S) data
qqbar, excited baryonic states (N*, *, *, *... ), hybrid, glueball, 1P1, c’
Best laboratory to elucidate a tricky situation; unique opportunity for QCD studies and new level of understanding
Interactions with charmed mesons
Absolute Br, decay constants, CKM elements (c), charmed baryons
Unique opportunities, results needed for advances in other area, e.g. b physics, thus complementary

37. Physics Program New study of the  lepton - lower limit on  mass;
- determination of m 0.1 MeV(needed in the future to test
lepton universality
- study of  weak current
- extend QCD studies
Precision R scan [at ~(1-3)% level)]
- Input for had(MZ2) and ahad, very important for testing
of SM and hunting for new physics beyond the SM
- Unique test of QCD (hadron production mechanism, e.g.
e+e- V, T, Baryon pairs
A real challenge experiment; may needs 100BESII R
data and good detector

38. Physics Program New physics - D0D0bar mixing
- CP violation in , J/, (2S) decays
- Lepton flavor violating processes
e.g. J/’, =e, , 
- Rare decay (e.g. J/DX, Non-SM  decay)
Taking advantage of threshold production and much
high statistics.

39. Status of BEPCII Project
Int. Review Meeting for feasibility study held in April 2-6. Both options are supported, double ring option is preferred.
Two options so far. A proposal will be delivered to government in May. Budget maintain at 40M US$ from government. Additional 20 M US$ is under discussion.
Detector has not well been defined, particularly for double ring machine
Part of R&D work started.
Expect to start running in

40. Data Collected with BES and May be with CLEOC and BESIII
Ecm(GeV)
Physics
BESI+BESII
CLEOC
BESIII
3.1
J/
7.8  106
5  107
109
109~1010
3.55 m
5 pb-1
>106(?)
3.69
(2S)
3.9  106
108(?)
108 ~109
3.77
(3770)
107
4.03 
1  103 ?
4.14
22.3 pb-1
106
4.6
105
2-5
R scan
6+85 pts (6.6%) 2% 3%

41. Comparison Ecm (GeV) L(cm-2s-1) /1032 Detector (generation)
Start Running Time
CLEOC/CESR
3-5
2-3.8
4th
BESIII/BEPCII
2-5
3-10
3rd

42. BES Entries in PDG 2000 Physics J/  D, Ds  Entry 34 45 5 2
Total 86 entries

43. Comments to CLEOC & BEPCII
Physics in tau-charm energy region is sill very rich in the B’s era. Many needs to be improved, many needs to be searched and some are expected to be discovered. BESII/BEPC is limited by both statistical and systematic uncertainties for the important mission.
Both CLEOC and BESIII are badly needed.
Any interesting and important physics result from single experiment is difficult to be accepted. Independent check and confirmation are needed. (A+D+L+O at LEP, CLEO, Babar+Belle for B physics)
CLEOC and BESIII will be the eminent players and contributors to the physics in tau-charm energy region in the world.

44. World J/ and (2S) Samples (/106)
2001

45. Suggestion and Wishes
Enhance the communication, scientific exchange between CLEO and BES
Some CLEO people join BES to practice BESII data for future CELOC physics; Some BES physicist join CLEO for future BESIII physics
CLEOC+BESIII=Competitors+Friends=More reliable physics results in tau-charm energy region
Wish both CLEOC and BESIII could be approved and started soon

46. Summary BES’s resent results
- Measured R in 2-5 GeV with an average uncertainties of ~6.6%.
- 5107 J/ events collected. Preliminary results on some of the radiative and hadronic decay using PWA reported.
The short term future to 2003 of the BES with BESII has not been fully decided. Possibly accumulate data at (2S), or (3770) or even scan R below 3 GeV
The future of the BES will be the BEPCII project 
Machine with L~3 /cm2·s, significantly upgrade BESII (BESIII). The commission may start from the end of 2005 or early 2006.