1. Study of New Hadron Spectroscopy at BESIII
Liu Fang (IHEP)
for BESIII Collaboration
The 9th National Workshop for Heavy Flavors and CP Violation
Hangzhou, Zhejiang, China

2. OUTLINE Latest results on new hadron spectroscopy Introduction
pp mass threshold enhancement in J/ and ’
radiative decays
Confirmation of X(1835) and observation of two new structures
Observation X(1870) in J/(+-)
Summary

3. Satellite view of BEPCII /BESIII
LINAC
South
2004: start BEPCII construction
2008: test run of BEPCII
2009-now: BECPII/BESIII
data taking
BESIII detector

4. BEPCII storage rings Beam energy: 1.0-2.3 GeV Design Luminosity:
1×1033 cm-2s-1
Optimum energy:
1.89 GeV
Energy spread:
5.16 ×10-4
No. of bunches: 93
Bunch length:
1.5 cm
Total current:
0.91 A
Circumference：
237m

5. BES Detector

6. Data samples So far BESIII has collected : BESIII will also collect:
2009: 225 Million J/(4 BESII)
2009: 106 Million ’ (4 CLEOC)
: 2.9 fb1 (3770)
(3.5  CLEO-c 0.818fb1)
- May 2011: MeV (one month) for Ds and XYZ spectroscopy
BESIII will also collect:
more J/, ’, (3770)
data at higher energies （for XYZ searches, R scan and Ds physics）

8. Light hadron
QCD allows different type of hadrons:

9. Observation of pp mass threshold enhancement
@BESIII
@BESIII
@BESIII

10. Observation of mass threshold enhancement @ BESII
3-body phase space
BESII
X(1860)
theoretical speculation:
bound state (baryonium)
FSI effect ……
0.1
0.2
0.3
acceptance
Mpp-2mp (GeV)
M= MeV/c2
G < 30 MeV/c2 (90% CL)
PRL 91 (2003) 10 10

11. Several non-observations
PRD 73 (2006)
EPJ C53 (2008) 15
No significant signal of X(1860) near threshold found
(only 2 significance)
PRL 99 (2007)
Mpp (GeV) 11 11

12. Observation of pp mass threshold enhancement at BESIII
0.1
0.2
0.3
M= MeV/c2
G < 38 MeV/c2 (90% CL)
M= MeV/c2
G < 30 MeV/c2 (90% CL)
PRL 91 (2003)
Chinese Physics C 34, 421 (2010)

13. PWA on the pp mass threshold structure in
BESIII
X(pp)
Preliminary
results ηc
Evident narrow ppbar mass threshold enhancement
Partial Wave Analysis (PWA):
Concentrate on dealing with the mass threshold structure, especially to determine the JPC (M(pp)<2.3GeV) .
Convariant tensor amplitudes (S. Dulat and B. S. Zou, Eur.Phys.J A 26:125, 2005).
Include the Juich-FSI effect (A. Sirbirtsen et al. Phys.Rev.D 71:054010, 2005). 13

14. PWA results and projections in
Preliminary results

15. Measurement for X(1860) >6.8σ better than other Jpc assignments.
PWA results are carefully checked from different aspects:
Contribution of additional resonances
Solution with different combinations
Different background levels and fitting mass ranges
Different BW formula
… …
All uncertainties are considered as systematic errors
Different FSI models Model dependent uncertainty
Spin-parity, mass, width and B.R. of X(1860):
Preliminary results
>6.8σ better than other Jpc assignments.

16. PWA on the pp mass threshold structure in
Preliminary results
BESIII
χcJ
Obviously different line shape of ppbar mass spectrum near threshold from that in J/ψ decays ηc
PWA results:
PWA Projection:
Significance of X(pp) is larger than 6.9σ.
The production ratio R:
It is suppressed compared with “12% rule”.
first measurement

17. Confirmation of X(1835) in and observation of two new structures
at BESIII

18. X(1835) at BESII
PRL 95,262001(2005)
LQCD predicts the 0-+ glueball mass is ~2.3GeV.
A 0-+ glueball may have similar property as c
(mainly decay into ).
J/+- was studied with 58M
Need to confirm X(1835) with BESIII ~225M J/ data !!! 18 18

19. Mass spectrum of X(1835) X(1835) and c are evident.
BES III
BES III
Combination for  to +- and 
X(1835) and c are evident.
Two additional structures are observed at M~2.1GeV and 2.3GeV
There maybe some f1(1510).
X(2370)
X(2120)

20. Fitting for the combined mass spectrum
Fitting with four resonances (acceptance weighted BW gauss)
Three background components:
Contribution from non-h’ events estimated by h’ mass sideband
Contribution from with re-weighting method
Contribution from “PS background”
Red line: estimated contribution of ①+ ②
Black line: total background
Stat. sig. is conservatively estimated:
fit range, background shape, contribution of extra resonances
BES III

21. X(1835) , X(2120), X(2370) at BESIII BESIII fit results:
Resonance
M( MeV/c2)
( MeV/c2)
Stat.Sig.
X(1835)
1836.5±
190.1±
>20σ
X(2120)
2122.4±
83±
7.2σ
X(2370)
2376.3±
83±
6.4σ
For the X(1835):
BESIII
X(1835) consistent with 0+
PWA is needed to understand
these structures. 21

22. Summary of X(1835), X(2120) & X(2370) in J/(’+-)
X(1835) resonance is confirmed at BESIII, but the width is significantly larger than that measured at BESII with one resonance in the fit.
Two new resonances, X(2120) and X(2370), are observed with significances larger than 7.2 and 6.4 respectively.
PWA is needed not only to determine the spin-parities of above three resonances, but also to make more precise measurements on masses, widths and BRs by considering possible interferences among them.

23. Observation X(1870) in J/X, Xa0(980)(+-)
X(1835) observed at BESII and then
confirmed at BESIII in J/→γπ+π-η´
theoretical interpretations: pseudoscalar
glueball, / excited states ..
study of its production in hadronic decays
to our surprise, we observed a new structure around 1.87 GeV

24. X(1870) in J/X, Xa0(980)
a0(980)
In addition to the well-known ’, f1(1285) and (1405), an unknown structure (denoted as X(1870)) around 1.87GeV/c2 is observed.
The f1(1285), (1405) and X(1870) primarily decay via a0(980)± mode.
M(+)
M()
With a0(980):
Veto a0(980):
M(+) non-a0(980)
M(a0(980))

25. Fitting results of X(1870)
Fitting with three resonances (acceptance weighted BW Gauss)
Background component described by Polynomial function
X(1870):
7.2
f1(1285)
(1405)
Contribution from non- and/or non-a0(980) BG events
Contribution from J/b1(1235)a0(980)
Contribution from “PS” process of J/a0(980)
M(a0(980))
BR(J/X, X )

26. Summary of X(1870) in J/(+-)
BESIII
arxiv :
Accepted by PRL.

27. Summary and Prospects
Huge data samples collected for charmonium decays at BESIII. A lot of results have been obtained,
The spin-parity of the pp mass threshold enhancement in J/γ pp was first determined as 0-+
Confirmation of X(1835) in J/  + and observation of two new structures X(2120) and X(2370) in J/   decays
Observation of new structure X(1870) in J/
We expect more exciting results in the coming years from BESIII.

28. many thanks for your attention !