1. Recent results on light hadron spectroscopy at BES
董燎原
(for BES Collaboration)
中国科学院高能物理研究所
中国物理学会高能物理分会
April

2. Outline Introduction of BES at BEPC
Introduction of Light hadron physics at BESIII
Observation of charged  at BESII
Confirmation of ppbar mass threshold
structure at BESIII
Confirmation of X(1835) at BESIII
Summary 2
2010/4/18 2 2

3. Beijing Electron Positron Collider (BEPC) at IHEP
BESI: Beijing Spectrometer I :
BESII: L ~ J/ Ebeam~ GeV
BESIII: (Physics run from March 2009)- ,
of designed value 3

4. 4
2018/9/19

5. Milestones of BESIII 5

6. 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.

7. Light hadron physics Motivation: Establish spectrum of light hadrons
Search for non-conventional hadrons
Understand how hadrons are formed
Study chiral symmetry in QCD
Why at a tau-charm collider ?
Gluon rich
Larger phase space than at higher energies
Clean environment, JPC filter
Glueball spectrum from LQCD
Y. Chen et al., PRD 73 (2006)
Many results in BESII:
~ 50 publications
Much more from BESIII:
100 statistics,
10 g resolution

8. Main contents in the study of the hadron spectroscopy
Meson spectrum（qq)
New forms of hadrons（glueballs,hybrid states, multi-quark states）
Baryon sectrum (qqq)

9. Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established. Searches for new forms of hadrons are of special importance at BES since J/psi decays are believed as an ideal factory to search and to study exotic hadrons BES-III can also play a very important role in the study of excited nucleons and hyperons, i.e., the very poorly understood N*、*、*、* and *++ resonances.

11. Observation of charged  at BESII

12. Observation of charged  at BESII
 was first found in K scattering data
However, its phase shift is much less than 180o and it cannot be filled into any nonets of ordinary mesons. There have been hot debates on the existence of .
In recent years:
FNAL E791 found evidence of neutral  in D+ K-++.
CLEO D0 K-+0 data find no evidence of .
FOCUS data on D+K-++ require K*0 interfere with either a
constant amplitude or a broad 0+ resonance in K.
BESII observed neutral  in J/  K*0K  KK in 2006.
neutral  pole: 12

13. The existence of charged  is expected !
CLEO reported the necessity of in
However, no charged  is needed in BABAR data.
BESII studied charged  in
BESII Preliminary
BESII Preliminary
K*(1410), K*(1430) 
(GeV/c2) again 13

14. Partial wave analysis results
BESII Preliminary
M(K) (GeV/c2)
M(K*(892)) (GeV/c2) 14
M(K*(892)K) (GeV/c2) 14

15. Resonance parameters of charged 
For reference, resonance parameters of neutral 
Different parameterizations of  give consistent results on the
pole of charged  .
The pole position for charged  is consistent with that for
neutral  within the error.
arXiv: [hep-ex] 15 15

16. threshold structure at BESIII
Confirmation of mass
threshold structure at BESIII

17. Observation of an anomalous enhancement near the threshold of mass spectrum at BES II
J/ygpp
acceptance weighted BW
X(1860)
M= MeV/c2
G < 30 MeV/c2 (90% CL)
theoretical
speculation:
bound state
FSI effects ……
c2/dof=56/56
0.1
0.2
0.3
3-body phase space
M(pp)-2mp (GeV)
Phys. Rev. Lett. 91, (2003)   
acceptance

18. The narrow threshold enhancement is NOT observed in those channels
PR D73, (2006)
EPJ C53 ,15 (2008)
PRL 99, (2007)
No significant narrow strong enhancement near threshold
(~2 if fitted with X(1860)) 18
Mpp (GeV/c2) 18 18

19. Observation of an anomalous enhancement near the threshold of mass spectrum at BES III
CPC(HEP & NP), 2010, 34(4):
Fitted with a S-wave BW, M= (stat)+7-26 (syst) MeV/c2
G < 38 MeV/c2 (90% CL) 19 19

20. This narrow threshold enhancement is also observed in at BESIII
BESIII preliminary

21. This narrow threshold enhancement is “NOT” observed in at BESIII
No significant narrow strong enhancement near threshold
Pure FSI interpretation disfavored 21 21 21

22. Confirmation of X(1835) at BESIII

23. Observation of X(1835) J/’+- at BESII
PRL 95,262001(2005)
Statistical Significance ~6 
Statistical Significance ~5.1 
To be confirmed with ~220M J/ data at BESIII 23 23 23 23

24. Mass spectrum of ’+- in J/’+-, ’
BESIII preliminary
BESIII preliminary
Significant peak at M~1835MeV
Statistic significance of X(1835) is about 18σ 24

25. Mass spectrum of ’+- in J/’+-, ’+-
BESIII preliminary
BESIII preliminary
Significant peak at M~1835MeV
Statistic significance of X(1835) is about 9σ 25

26. ??? Combined mass spectrum of the two decay modes
Structures at higher mass region???
BESIII preliminary
X(1835) is confirmed in BESIII and the significance increases as statistics increases
BESII 26

27. Summary
BEPCII/BESIII is a major upgrade of the BESII experiment at the BEPC accelerator for studies of hadron spectroscopy and -charm physics.
BESIII has been in operation since 2008: ~110M ’ and ~220M J/ events have been collected
Recent results at on light hadron BES are presented:
Partial wave analysis of charged  at BESII
Confirmation of ppbar mass threshold structure at BESIII
Confirmation of X(1835) at BESIII
More Exciting results are expected. 27

28. THANK YOU!

29. Data Accumulated @ BESIII
Pb-1
Pb-1
Pb-1 29

30. Achieved Luminosity 30

31. Physics potential at BESIII
The physics window is precision charm physics and the search for new physics.
High statistics: high luminosity machine + high quality detector.
Small systematic error: high quality detector. 31
2018/9/19