1. New Observations at BESII and Prospects at BESIII/BEPCII
Shan JIN
(for BES Collaboration)
Institute of High Energy Physics (IHEP)
DIF 06
Frascati, March 1, 2006

2. Outline New Observatins at BESII Prospects at BESIII/BEPCII
A possible bound state: mass threshold enhancement in and new observation of X(1835).
mass threshold enhancement in
 mass threshold enhancement in J/  
Prospects at BESIII/BEPCII

3. 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.

4. 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 the hottest topic in the hadron spectroscopy.

5. 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.

6. BESII 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= 8.5 %  = 7.9 mr B field: T
p/p=1.7%(1+p2) z = 2.3 cm

7. World J/ and (2S) Samples (106)
Largest from BES
J/
(2S)
2001
2002

8. A possible ppbar bound state

9. Observation of an anomalous enhancement near the threshold of mass spectrum at BES II
J/ygpp
acceptance weighted BW
M= MeV/c2
G < 30 MeV/c2 (90% CL)
c2/dof=56/56
0.1
0.2
0.3
Phys. Rev. Lett. 91, (2003)   
M(pp)-2mp (GeV)
3-body phase space
acceptance

10. NO strong dynamical threshold enhancement in cross sections (at LEAR)
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 !
|M|2
|M|2
BES
BES
Both arbitrary normalization
Both arbitrary normalization

11. 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.

12. In ppbar collision, the background is much lager (I)
J/ decays do not suffer large t-channel “background” as ppbar collision.
>>

13. In ppbar collision, the background is much lager (II)
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
I=1 S-wave
P-wave
I=0 S-wave
A.Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G. Meißner, A.W. Thomas, Phys.Rev.D71:054010, 2005

14. 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

15. This narrow threshold enhancement is NOT observed in B decays
The structure in B decays is obviously different from the BES observation:
Belle
The structure in B decays is much wider and is not really at threshold.
It can be explained by fragmentation mechanism.
BES II
Threshold enhancement in J/ decays
is obviously much more narrow and
just at threshold, and it cannot be
explained by fragmentation mechanism.

16. 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 =  6.7 MeV
 = 0  93 MeV

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

18. X(1830) 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)
Considering that decaying into ppbar is only from
the tail of X(1830) and the phase space is very small,
such a BR indicates X(1830) has large coupling to ppbar !

19. pp bound state (baryonium)?
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)
Datta, P.J. O’Donnell, PLB 567, 273 (2003)]
M.L. Yan et al., hep-ph/
B. Loiseau et al., hep-ph/
deuteron:
baryonium:
attractive nuclear force
attractive force? + n + -
loosely bound 3-q 3-q color singlets with Md = 2mp- e
loosely bound
3-q 3-q color singlets with Mb = 2mp-d ?
Observations of this structure in other decay modes are desirable.

20. What do we expect from J/psigamma 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.

21. New Observation of X(1835) in
PRL 95, (2005)

22. Analysis of
X(1835)
5.1 

23. Analysis of
X(1835)
6.0 

24. Observation of X(1835) in
Statistical Significance 7.7 
The +- mass spectrum for  decaying into +- and  

25. Mass spectrum fitting 7.7
The +- mass spectrum for  decaying into +- and  
7.7
BESII Preliminary

26. Comparison of two decay modes
Mass and width from
m=1827.48.1MeV/c2 , =54.234.5MeV/c2
m=1836.37.9MeV/c2 , =70.323.1MeV/c2
The mass, width and branching fractions obtained from two different decay modes are consistent with each other.

27. 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 =  6.7 MeV
 = < 153
In good agreement with X(1835)

28. 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.

29. Observation of mass threshold enhancement in

30. Observation of an anomalous enhancement near the threshold of mass spectrum at BES II
3-body phase space
Phys. Rev. Lett. 93, (2004)   
For a S-wave BW fit: M = 2075 12  5 MeV
Γ = 90  35  9 MeV

31. Possible Interpretations
FSI？ Theoretical calculations are needed.
Conventional K* or a multiquark resonance？
Search for its Kπ 、Kππ decay modes would help to understand its nature.
We are now studying
J/  KKπ 、KKππ

32. K mass threshold enhancement

33. Observation of a strong enhancement near the threshold of mass spectrum at BES II
NX*
BES II
PS, eff. corrected
(Arbitrary normalization)

34. 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 ~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.

35. 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.
hep-ph/ )
Ecm – ( MΛ+MK ) (MeV)

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

37. Observation of  mass threshold enhancement

38. We studied DOZI process:
J/    +  
 
+-0 K+ K-

39. Clear  and  signals   
recoiling against 

40. Daliz Plot

41. A clear mass threshold enhancement is observed
Acceptance

42. Side-bands do not have mass threshold enhancement

43. 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 1052028 MeV, and the corresponding branch ration is (2.610.270.65)x10-4.
It should be observed in KK mode. Its relation with f0(1710),f0(1790)?

44. Is the STRONG threshold enhancement universal/naïve in J/ decays
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

45. Summary of BESII New Observations (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 since it can easily fall apart into two or more mesons.
I can see
f0(980)
I can see broad  under other peaks
broad
resonance or phase space?
any broad
resonance
under other peaks?

46. Summary of BESII New Observations (II)
Summary (II)
A unique very narrow and strong mass threshold enhancement is observed in decays at BES II:
It is not observed in cross sections.
It is not observed in B decays.
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.

47. Summary of BESII New Observations (III)
Summary (III)
Summary of BESII New Observations (III)
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/  
J/ψ decay is an ideal place to study exotic structures.

48. Prospects at BESIII/BEPCII

49. The need for upgrade Interesting physics limited by statistics:
glueball/hybrid/multi-quark searches,
CKM matrix elements, DDbar mixing,
rp puzzle, non-pQCD…
Large systematic errors due to limited resolutions of the detector
Detector is aging
Multi-bunch mode & High event rate

50. We are unique In a regime of transition between pQCD and non-pQCD
Can provide calibrations and tests of LQCD
Rich spectra of light hadrons for Quark model test and for searches of new hadrons
Rich gluonic matter production for QCD test
Near the production threshold of tau-charm

51. Physics at BEPCII/BESIII
Light hadron spectroscopy
QCD and hadron production
Charmonium physics
Precision measurement of CKM matrix elements
Precision test of Standard Model
Search for new physics/new particles

52. BEPCII Design goal Collision Mode SR Mode Beam energy range 1-2.1 GeV
Optimized beam energy GeV
Luminosity 1  1033 GeV
Full energy injection GeV
SR Mode
Beam energy GeV
Beam current mA

53. Event statistics at BESIII
Physics
Channel
Energy
(GeV)
Luminosity
(1033 cm–2s –1)
Events/year
J/y
3.097
0.6
1.0×1010 t
3.67
1.0
1.2×107 y’
3.686
3.0 ×109 D
3.77
2.5×107 Ds
4.03
1.0×106
4.14
2.0×106
*CLEO took 10 nb D production cross section while we took 5 nb

54. Precision measurement of CKM: Branching rations of charm mesons
Vcd /Vcs: Leptonic and semi-leptonic decays
Vcb: Hadronic decays
Vtd /Vts: fD and fDs from Leptonic decays
Vub: Form factors of semi-leptonic
decays
Unitarity Test of CKM matrix

55. CKM matrix elements measurement
Current
BESIII
Vub
25% 5%
Vcd 7% 1%
Vcs
16%
Vcb 3%
Vtd
36%
Vts
39%

56. Precision test of SM and Search for new Physics
DDbar mixing
DDbar mixing in SM ~ 10 – –10
DDbar mixing sensitive to “new physics”
Our sensitivity : ~ 10-4
Lepton universality
CP violation
Rare decays
FCNC, Lepton no. violation, ...

57. QCD and hadron production
R-value measurement
pQCD and non-pQCD boundary
Measurement of as at low energies
Hadron production at J/y, y’, and continium
Multiplicity and other topology of hadron event
BEC, correlations, form factors, resonance, etc.

58. R-value measurement Errors on R will be reduced to 2% from current 6%
Error on R
Da(5)had (MZ2)
5.9% ± 3% ± 2% ±
Errors on R will be
reduced to 2% from
current 6%

59. BEPC II Storage ring: Large angle, double-ringRF SR RF e + e - IP

60. Double ring installation – Wood model
No spacing problems

61. Mass production of the most ring components is completed。
Storage rings
Mass production of the most ring components is completed。

62. Installation of linac is complete

63. Production of IR equipment

64. CsI(Tl) calorimeter, 2.5 %@1 GeV
The BESIII Detector
SC magnet, 1T
Magnet yoke
RPC
TOF, 90ps
Be beam pipe
MDC, 120 mm
CsI(Tl) calorimeter, 2.5 GeV

65. Main drift chamber Rin: 63mm; Rout: 810mm; length: 2400 mm
Inner cylinder: 1 mm Carbon fiber,
outer cylinder: 10 mm Carbon fiber with 8 windows
End flange: 18 mm thick Al 7075 ( 6 steps)
7000 Signal wires: 25(3% Rhenium) mm gold-plated tungsten
22000 Field wires: 110 mm gold-plated Aluminum
Small cell: inner---6*6 mm2, outer *8.2 mm2,
Gas: He + C3H8 (60/40)
Momentum
dE/dX resolution: ~ 6%.

66. Beam test at KEK
Weighted average s ~ 93 mm

68. CsI(Tl) crystal calorimeter
Barrel: 5280 crystals，Endcap: 960 crystals
each crystals (5.2x 5.2 – 6.4 x 6.4) x 28cm3
Readout: Photodiodes, 1cm2cm,
Energy range：20MeV – 2 GeV
Energy resolution:
position resolution: 6
Tiled angle: theta ~ 1-3o, phi ~ 1.5o

69. Crystal production will be completed soon.
Assembly should start soon, but the mechanics for the barrel is delayed by ~ two months.
Mechanics for the endcap should go out for bid soon
By the end of the year, the assembly should be completed

70. Structure of TOF Aim: particle identification (PID)
Barrel TOF
Endcap TOF
Scintillator: 2.4 m long, 5cm thick

71. TOF
70±2ps
104±11ps
94±3ps 质子 电子
Time resolution from a beam test of the Prototype（including scintillator,PMT, preamp., electronics, cable)
PMT and scintillator ordered

72. m system : RPC 9 layer, 2000 m2 Bakelites and glass, no lineseed oil
4cm strips, channels
Tens of prototypes (up to 1*0.6 m2 )
Noise less than 0.2 Hz/cm2

74. The super-conducting magnet in place

75. Trigger and DAQ The trigger design is almost finalized.
No. of types of trigger boards are reduced from 23 to 17
All the boards are tested, some for several prototyping.
By the end of the year, all the boards should be tested and installed.
The whole DAQ system tested
to 8K Hz for the event size of
12Kb, a factor of two safety
margin
during beam test with MDC
and EMC

76. Offline software
Beta release on

78. Physics preparation
Write a yellow book on BESIII physics: a summary of theoretical and experimental tau-charm physics and the BESIII physics reach
Workshops：
Charm 2006: International tau-Charm workshop Beijing June ,
US-China workshop on HEP cooperation
Charm2006: Workshop on Tau-Charm Physics
June 5 – 7, 2006, Beijing, China

79. Welcome to join in BESIII
谢 谢！ Thank You!

80. Pure FSI disfavored (I)
Theoretical calculation (Zou and Chiang, PRD (2003)) shows: The enhancement caused by one-pion-exchange (OPE) FSI is too small to explain the BES structure.
The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI.
|M|2
|M|2
BES
BES
Both arbitrary normalization
Both arbitrary normalization
one-pion-exchange FSI
Coulomb interaction

81. 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
P-wave
I=0 S-wave

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

83. So, pure FSI is disfavored
So, pure FSI is disfavored. However, we do not exclude the contribution from FSI.

84. From B.S. Zou, Exotics 05: From A. Sirbirtsev :
`pp near threshold enhancement is very likely
due to some broad sub-threshold 0-+ resonance(s)
plus FSI.
From A. Sirbirtsev :
FSI factors should be included in BW fit.

85. Discussion on I=1 S-wave FSI

86. Pure FSI disfavored (III) — I = 1
Pure I=1 S-wave FSI is disfavored by more than 3 .
FSI + BW
Pure FSI
M =  21 MeV
 = 0  191 MeV

87. 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.

88. 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.

89. ppbar bound state in NNbar potential
Paris NNbar potential: ( Paris 93, B. Loiseau et al., hep-ph/ , )
For 11S0 , there is a bound state:
E = i 26.3 MeV
quite close to the BES observation.
However, Julich NNbar model: ( A. Sibirtsev et al., hep-ph/ )
For 11S0 : E = i 413 MeV
seems quite far away from BES observation.
They both predict an 11S0 ppbar bound state, although they are quantitatively different.

90. BES II Preliminary
No (1800)

91. NO strong dynamical threshold enhancement in cross sections (at LEAR)
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 !
|M|2
|M|2
BES
BES
Both arbitrary normalization
Both arbitrary normalization

92. This enhancement is NOT observed in process at SAPHIR

93. Discussion on KΛ mass threshold enhancement NX(1610)
NX(1610) has strong coupling to KΛ:
From (S&D-wave decay) 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)

94. 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.

95. Similar enhancement also observed in
4 away from phase space.