1. The highlights at BES-I, II, III
Zhi-yong Wang
For BESIII Collaboration
Dec., 20, 2016
Academia, Sinica, Taibei

2. (Beijing Electron Positron Collider)

3. BEPC sketch 202m Storage ring (240m) west south Test beam linac BESIII
Synchrotron radiation
west
south

4. Outline History (Construction, upgrade) Physics program Summay
Light Hadron
Charmonium (like-charmonium)
Charm
QCD
New Physics
Summay

5. BES (BEijing Spectroscpy) history (I)
Start to construct at 1984 (called BES-I later)
first collision at 1988
Data collection from 1991
-scan
9M J/
3.7M (2S)
22.3pb-1 at Ecm=4.03 GeV for Ds study.
BES-I highlights
 mass measurement (Natural science award, state-level, second-order)
Charmonium study (same as before)
fDs measurement (Natural science award, municipal-level, second-order)

6. BES history (II)
First upgrade in 1995, the performance of TOF was improved a lot. BESIBESII
Data collection
58M J/
14M (2S)
R-scan at 2-5 GeV
(3770) scan & data taking
BESII highlight
X(1835) threshold enhancement (Natural science award, state-level, second-order )
R value measurement (same as before)
(3770) non-DD decay (same as before)
Charmonium study (Natural science award, municipal-level, second-order)

8. BES history （III）
2004, second upgrade, BESIIBESIII. Meanwhile, BEPCIBEPCII.
BESIII is an entirely new detector, the performance of each sub-detector is much better than BESII
The luminosity of BEPCII is 100 times larger than before.

11. BESIII physics program
-charm
charm
-QCD
Charmonium (-like)
New physics
Light hadron

12. Physics program I: Light hadron

13. Stimulated

14. Glueball search (J/ radiative decay)0+ 2+ 0-
J/ψ→γPP
J/ψ→γVV
J/ψ→γPPP
Coupled channel analysis needed
J//00/ (PRD92 (2015) , PRD87, (2013),092009) (PP mode)
J///, (PRD87, (2013), , PRD93, (2015),112011) (VV mode)
J/KSKS (PRL115, ) (PPP mode)

15. Search and study excited baryon
Issue of Missing Baryons: Quark models predict many more baryons than what have been observed

16. Published paper on baryon spectrum
J/pp0/, PRL110, , (2013)
J/pK, PRD88, , (2013)
(3686), cJ  pK, PRD87, , (2013)
(3686), PRD88, , (2013)

17. Light meson decay：test some theoretical models
Unique place to test fundamental symmetries in QCD at low energy region
Probe physics beyond the Standard Model (SM) ,
E.g.
η/η’ →2γ chiral anomaly
η/η’ →π+π-π quark masses
η’→γπ+π box anomaly
η/η’ →ππ CP violation
η/η’ → μ+μ-π0 ,e+e-π0 C violation
η/η’ → μ e LF violation

18. Published (submitted) paper on light meson study
4， PRL112, (2014)
e+e, PRD92, (2015)
 e+e, PRD92, (2015)
 +0, PRD92, (2015)
 3, arXiv:1606:03847
a0(980)f0(980) mixing, PRD83, (2011)

19. Physics program II: Charmonium (-like)

20. Charmonium spectrum

21. (2S) samples in the world

22. (2S)0hc transition (inclusive mode)
BESIII: PRL 104, (2010)
Mass: 0.130.18 MeV
Width: 0.730.450.28 MeV
(< % C.L.)
Top: (2S)0hc , hcc, canything (E1-photon-tagged)
Bottom: (2S)0hc , hcanything
BESIII
BESIII
Combined inclusive and E1-photon-tagged spectrum (First measurements)
B[y(2S)p0hc] = [ 8.4±1.3(stat.) ±1.0(syst.)]×10-4
B(hcghc) = [54.3±6.7(stat.) ±5.2(syst.)] %
Agree with predictions of Kuang, Godfrey, Dudek, et al.

23. (2S)0hc ,hcc,c16 exclusive channels
PRD86， (2012)
BESIII
16 modes, 832 events
Mass: 0.110.15 MeV
Width: 0.700.280.25 MeV
CLEOc: PRL101, (2008)
Mass: 0.190.12 MeV
Width: fixed to 0.9 MeV
The measured mass and width are very consistent with those from inclusive mode

24. New hc decay modes
PRL116， (2016)
B(hc’) =
(1.520.270.29)‰
B(hc) =
(0.470.150.14)‰
R= B(hc) / B(hc’)
= (30.711.38.7)%
First observation of hc radiative decays to light hadron! Data can be used to determine -’ mixing angle —— any help to understand J/ and ’ decay puzzles?

25. c parameter measurement via (2S)c
BESIII：PRL108, (2012)
KsKp
K+K-p0
p+p-h
KsK3p
2K2pp0 6p
Mass = ±0.6±0.6 MeV/c2
Width = 32.0±1.2±1.0 MeV
First observation of the interference between c resonance and non-resonance.

26. First observation of E1 transition: (2S)c
Significance > 10s !
BESIII: PRL109, (2012)
With the measured Br(KK) from Belle Collaboration, we measured
Br(y’ghc)=(6.8±1.1±4.5) ×10-4
(theoretical prediction: ( )10-4 )

27. Study on XYZ states ? We focus on XYZ since 2011！ What are they ?
Charmonium?
Hybrid?
Tetraquark?
Molecule? …
Z(4430)
Z(4250)
Z(4050) ?
X(3872)
XYZ(3940)
X(3915)
X(4160)
Y(4008)
Y(4140)
Y(4260)
Y(4360)
X(4350)
Y(4660)
Godfrey & Isgur,
PRD32, 189 (1985)
We focus on XYZ since 2011！

28. Charmnonium spectrum We focus on XYZ since 2011
Below the open charm threshold the spectrums well understood
very good agreement between predicted and discovered states
Above the threshold the situation in more complex
only few of the predicted states have been found
in the last decades many new states have been observed with properties that are not consistent with expectations for charmonium: X, Y, Z
X states:
charmonium-like states with JPC ≠ 1−−
Observed in B decays, pp and pp collisions
Y states:
charmonium-like states with JPC = 1−−
Observed in direct e + e - annihilation or in ISR
Z states:
Must contain at least a cc and a light qq pair
We focus on XYZ since 2011

29. Data samples for XYZ study (>9/fb)
4180
4600
4230
4420
4260
4010
4360
4470
4530
4210
4310
3810
3900
4090
4220
4245
4390
For the XYZ states study, from the end of 2012, BESIII has accumulated about 3.3 inverse fb data at 14 energy points. Around psi(4040), Y(4260), and Y(4360) peaks, we collected the largest data sample in the world so far for the study of its decays, and data samples with small statistics at another 10 energy points are collected for the line-shape study of these vector states.
4420
4575
4190

30. The Zc states

31. First observation of Zc(3900)
BESIII announced the observation of Zc(3900) in Mar., 26, 2013, which contains at least 4-quarks, and was confirmed by Belle and CLEO-c Collaboration soon。
Comments ：
《Nature》: open a new door to world。
《Physical Review Letters》：implies an existence of tera-quark state
Top 1 in the 11 great results selected by American Physics magazine.
recorded by PDG2014，the only and one new particle founded in China！

32. Comparison of obsered Zc(3900)
CLEO-c
M = 3.64.9 MeV
 = 461020 MeV
307  48 events
Significance >8
M = 6.64.5 MeV
 = 632426 MeV
159  49 events
Significance >5.2
M = 388551 MeV
 = 34124 MeV
81  20 events
Significance >6.1
PRL110,
PRL110,
PLB, 727(2013) 366

33. The neutral isospin partner: Zc(3900)0
PRL 115, (2015)
A structure on  0 J/ψ invariant mass spectrum observed:
Mass = ±2.3±2.7 MeV
Width = 29.6±8.2±8.2 MeV
Significance = 10.4 s
GeV (PLB 727, 366)
3.7!

34. Observation of Zc(3885)±(0) in 𝐞 + 𝐞 − → 𝛑 ±(𝟎) (𝐃 𝐃 ∗ ) ∓(𝟎)
PRL 115， (2015)
PRL 112, (2014)

35. Comparison: Zc(3885)± and Zc(3900)±
Single D tag results,
PRL 112, (2014)
The mass and width are consistent within 2!
Different dynamics in Y(4260)-Zc(3900) system!

36. Observation of Zc(4020)+(0) in ee(00) hc
BESIII: PRL111,
Fit results
Charged Zc(4020)±
Mass=(4022.9±0.8±2.7) MeV
Width=(7.9±2.7±2.6) MeV
Significance: >8.9s
Neutral Zc(4020)0
Mass=(4023.9±2.2±3.8) MeV
Width: fixed to charged partner
Significance: 5s
PRL (2014)

37. Observation of e+e (0)Zc(4025)+(0) (0)D*D*
RM(0) (GeV/c2)
PRL (2014)
PRL (2015)
if Zc(4025)± is the Zc(4020)±observed in the π±hc spectrum:

38. Summary Zc states at BESIII
e+e + (D*D*)
e+e 0(D*D*)0

39. Zs search：observation of
Y(2175）in J/
Y(2175) was observed by Babar and confirmed by BESII, Belle and Babar.
What is Y(2175)’s nature? A strange analogy to Y(4260)?
Phys.Rev. D91 (2015),
Study of Y(2175) with high statistics is necessary
Using 225 million of J/ψ，
The production branching fraction is measured
Resonance parameters consist with previous experiments

40. Zs search：e+e 
ZS ?
ZcJ/
Zb(nS)
EPJC 72，2008（2012）

41. The X states

42. What is the X(3872) (the first observed X state)?
Belle, 2003
140/fb
Mass: Very close to D0D*0 threshold
Width: Very narrow, < 1.2 MeV
JPC=1++
Production
in pp/pp collison – rate similar to charmonia
In B decays – KX similar to cc, K*X smaller than cc
Y(4260)+X(3872)
Decay BR: open charm ~ 50%, charmonium~O(%)
Nature (very likely exotic)
Loosely D0D*0 bound state (like deuteron?)?
Mixture of excited c1 and D0D*0 bound state?
Many other possibilities (if it is not ’c1, where is ’c1?)
M(J/) –M(J/) [GeV]
The X(3872) was first observed by Belle ten years ago, then confirmed by other experiments[CDF, D0 BaBar], its mass is very close to neutral DD* threshold and its width is very narrow. Since its observation, it has stimulated special interests on its nature. In both Belle and BaBar, its decay to gamma Jpsi has been observed, which supports it being a C-even state. The angular distribution study from CDF and most recently from LHCb determined it being a 1++ state. In the theoretical side, it was interpreted as a good candidate for a hadronic molecule or a tatrequark state. Currently, X(3872) was only observed in B decays, proton proton collision. Since its quantum number is determined to be 1++, it could be produced trough radiative transition of a vector charmonium or charmonium-like states, such as excited psi or Y states.

43. Observation of e+e X(3872)J/
PRL 112, (2014)
N(X(3872)) = 20.1 
M(X(3872)) = 0.70.2 MeV [PDG: 0.17 MeV]
The pipijpsi mass distribution summed over all the energy points is fitted to extract the mass and signal yields of the X(3872). The X(3872) signal is described by a MC simulated signal shape convolving a Gaussian function which represents the difference between data and MC, while the background events are described by a linear function. The mass resolution difference between data and MC simulation, the absolute mass and the cross section calibration are obtained using the ISR psip signal. The fit yields 20 X(3872) signal events with a mass consistent with the PDG value. The statistical significance of X(3872) is estimated to be 6.3 Gaussian standard deviation.

44. Evidence for the X(3823) at Belle
arXiv: (PRL111, (2013))
711 fb-1
3.8σ
B χc1γK
The measured mass and width are consistent with the missing Ψ2(1D) state
BESIII may search for it!
M(χc1γ) (GeV/c2)

45. e+e-p+p-X(3823)p+p-gcc1
PRL 115, (2015)
X(3823)
significance: 6.2s, observation !
M=3821.7±1.3±0.7 MeV
Width<16 90% C.L.
X(3823) as the y(13D2) candidate

46. The Y states

47. Cross section of e+e +-J//hc
arXiv:
arXiv:
BESIII observed the production of pi+pi-h_c with the data samples at a few energy points. Here, hc is reconstructed with its E1 transition to eta_c, and eta_c is reconstructed with its 16 hadronic decay modes. From the plot we can see very clear eta_c signal in the invariant mass of the hadronic system, and very clear h_c signal at gamma and eta_c invariant mass. If we select only the events in the eta_c mass region, we get …

48. Observation of e+e- cJ
Fit with a single BW
Mass = 4226±8±6 MeV
Width = 39±12±2 MeV
Significance > 9s
e+e- c2:
Agree with from (4415) with
BR=(1.4±0.5)×10-3 (sol. I), or
BR=(6±1)×10-3 (sol. II)
Using the signal events observed, the Born cross section times the branching fraction of X(3872) decays into pipijpsi are calculated as listed in this table. For 4009 data and 4360 data, since the signals are not significant, upper limits on the production rates at 90% confidence level are set. The observation suggests that the X(3872) might be from the radiative transition of the Y(4260). Combining the cross section of electron positron goes to pi pi jpsi measured by BESIII and take the branching fraction of X(3872) decays to pi pi jpsi as 5 percent, the cross section ratio of Y(4260) decays into gamma X(3872) to Y(4260) decays into pipijpsi is about 11 percent, which is a relatively large transition ratio.
Need data beyond 4.6 GeV to check structure in c1.
c0
PRD93, (2016)

49. Physics program III: charm

50. Major goals charm meson: D0(+), Ds+
Leptonic and semileptonic decays: fD(s)+, fK(p)+(0), |Vcs(d)|
Vcs(d)依赖于LQCD fDK(p)+(0)计算精度
Hadronic decays:
Parameters of D0D0 mixing and CP violation
Strong phase difference in D0 and D0: constrain g/f3
charm baryon: Lc+
Absolute branching fractions

51. Low background level, large BF, small systematic ucertainty
Data samples
2010 and 2011: 2.93 fb-1 data at GeV (3.6×CLEO-c)
2011: 482 pb-1 data GeV (aim to XYZ, the largest e+e- data at GeV, but Ds+ sample is not so competitive with the one from 600 pb-1 data at 4.17 GeV at CLEO-c)
2014: 567 pb-1 data at 4.6 GeV (the largest e+e- data at Lc+Lc- threshold)
Pair GeV, D(s)0(+) or Lc+ K+
Single Tag π- D- π-
y’’ e+ e-
2016: 3fb-1 data at 4.18 GeV D+ m+ v
Double Tag
Low background level, large BF, small systematic ucertainty

52. D+ decay constant & mixing matrix |Vcd|
e+e-y(3770)D+D-
PRD89(2014)051104R
D-K+p-p-
D-Ksp-
D-KsK-
D-K+K-p-
D-K+p-p-p0
D-p-p-p+
D-Ksp-p0
D-K+p-p-p-p+
D-Ksp-p-p+
B[D+m+n]=(3.710.190.06)×10-4
fD+=(203.25.31.8) MeV
|Vcd|=0.22100.00580.0047
Most precise fD+
First measurement of|Vcd| via pure lepton channel

53. Comparisons of existing fD+, fDs+ and fD+:fDs+
High theoretical precision for fD+, fDs+, fD+:fDs(0.5%, 0.5%, 0.3%) is a huge challenge to experiment
~2 deviation for fD+, fDs+, fD+:fDs+ between prediction and experiment
Experiments
Femilab Lattice+MILC (2014)
HPQCD (2012)
Averaged
Expected D
fD+(MeV)
203.94.7
212.6
1.8s
208.33.4
0.8s
fDs+(MeV)
256.94.4
249.0
1.7s
246.03.6
1.4s
fD+:fDs+
1.2600.036
1.1712
2.5s
1.1870.013
1.9s

54. D0D0mixing parameter: yCP
PLB 744(2015)339

55. BFs Measurement of Lc+ exclusive decay
ST: ~15000
DT: ~1000
PRL116(2016)052001

56. First absolute BF of Lc+  Ll+v
PRL115(2015)221805
Prediction: ( )%
B[Lc+Le+n]=(3.630.380.20)%
B[Lc+Lm+nm]=(3.490.460.26)%
arXiv:

57. Program IV：-QCD

58.  mass measurement Mτ / Mτ = 9.6  10–5
= 9.6  10–5
Lepton universality can be tested at 0.4%
Phys. Rev. D90, (2014)

59. R value measurement defination： R value is an essential parameter
Experimentally：
Nhad: Number of hadron
Nbg: Number of background
L: luminosity
had: detection efficiency for hadron events
: ISR factor
Measurement precision：BESII 6～7%  BESIII 3%

60. R is the input of (MZ2) and a
Burkhardt, Pietrzyk 2011
BEPC
3.6
BEPC
精度将提高 4 倍！ (FNAL-989, 2015)
aexp = ( ±6.3) ×10 –10 (E821)
a SM = ( ±4.9) ×10 –10
G.S. Huang: 973 tau-QCD
Davier 2010
BEPCII能区仍然是第二大误差来源！

61. R measurement at BESII
R measurement at BESIII with more energy points is in progress

62. Measurement of excited charmonium
Resonance shapes
Interference term
Rres=RBW+Rint
Phys.Lett.B660,315(2008)
BESII
, Lu An
G.S. Huang: 973 tau-QCD

63. Proton form factor Phys. Rev. D 91, 112004 (2015) Analysis Features:
Radiative corrections from Phokhara8.0 (scan)
Normalization to e+e-  e+e-, e+e- γγ
(BABAYAGA 3.5)
Efficiencies 60% (2.23 GeV) % (~4 GeV)
 GE/GM  ratio obtained for 3 c.m. energies
Ecm/GeV
Lint / pb-1
2.23
2.6
2.40
3.4
2.80
3.8
3.05, 3.06, 3.08
60.7
3.40, 3.50, 3.54, 3.56
23.3
3.60, 3.65, 3.67
63.0
, Lu An
G.S. Huang: 973 tau-QCD

64. Measurement of Collins Effect
Motivation: Input for SIDIS experiments to extract spin-dependent parton distribution without energy evolution
Method: Probing azimuthal asymmetries of di-hadron.
PRL 116, (2016)
non-zero asymmetries
growing with fractional energy z
vs. z1,z2
vs. pt
, Lu An
G.S. Huang: 973 tau-QCD

65. Program V：new physics

66. Search for the forbidden decay

67. Rare decay

68. Exotic decay
PRL100，(2008)

69. Summary
BES has 3 generations, BESI,II,III and run for about 30 years.
The physics program at BES covers light hadron, charmonium(-like), charm, -QCD, and new physics.
A lots of robust results are obtained, for example,  mass and R value measurements, the observation of X(1835) and Zc(3900), non-DD decay of (3770), and so on.
Thank you!