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Physics at BES. Shan JIN (for the BESIII Collaboration) Institute of High Energy Physics (IHEP) USTRON09, Poland September 12-16, 2009. Outline. Introduction of BES experiments and Physics at BES Highlights at BESII Status of BESIII and preliminary results

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physics at bes

Physics at BES

Shan JIN

(for the BESIII Collaboration)

Institute of High Energy Physics (IHEP)

USTRON09, Poland

September 12-16, 2009

  • Introduction of BES experiments and Physics at BES
  • Highlights at BESII
  • Status of BESIII and preliminary results
  • Future prospects at BESIII
  • Conclusion

Beijing Electron Positron Collider (BEPC) at IHEP


Storage Ring

BESI: 1989-1998

BESII: 1999-2004

L ~ 51030 /cm2s at J/

Ebeam~ 1 – 2.5 GeV



BESIII: 2008-

Physics run started in March, 2009. 100M (2S) and 200M J/ events collected

BEPCII: L reached 31032/cm2sat (3770)

designed L: 1033/cm2s








why tau charm physics is interesting
Why tau-charm physics is interesting

in the past

in the era of LHC

in the future

Abundant resonances(J/y family, huge Xsections)

Tau-charm threshold production(in pairs tagging  background free, no fragmentation, kinematic constrains, quantum coherence,…)

Charm quark: A bridge between pQCD and non-pQCD

A ruler for LQCD

J/y decay Gluon rich environment

Flavor physics Complementary to LHC: virtual vs real

A broad spectrum & efficient machine:

what highlight physics interested us
What (highlight) physics interested us


  • Light hadron spectroscopy
    • Full spectra: normal & exotic hadrons QCD
    • How quarks form a hadron ? non-pQCD
  • Charm physics
    • CKM matrix elements  SM and beyond
    • mixing and CPV  SM and beyond
  • Charmonium physics
    • Spectroscopy and transition  pQCD & non-pQCD
    • New states above open charm thresholds  exotic hadrons ?
    • pQCD: rp puzzle  a probe to non-pQCD or ?
  • Tau physics and QCD
    • Precision measurement of the tau mass and R value
  • Search for rare and forbidden decays

Precision test of SM and search for new physics

light hadron spectroscopy
Light hadron spectroscopy

Glueball spectrum from LQCD

Many results in BESII:

~ 50 publications

Much more from BESIII:

100 statistics,

10 g resolution

  • 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

Y. Chen et al., PRD 73 (2006) 014516


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( qq )

Baryon(q q q)

How quarks/gluons form a hadron is far from being well understood.


Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established.However, the effort has never been stopped, especially, during the past three years, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model. 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.

charmonium physics
Charmonium physics
  • Examples of interesting/long standing issues:
  • rp puzzle
  • Missing states ?
  • Mixing states ?
  • New states above open charm thre.(X,Y,Z,…)
  • What to study ?
    • Production, decays, transition, spectrum
  • For what ?
    • A lab for pQCD and non-pQCD
    • Calibrate LQCD
    • How quarks form a hadron ?
  • Why at a tau-charm collider ?
    • A clean environment
    • Tagging possible
    • Abundantly produced


VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm

MDC: xy = 220 m BSC: E/E= 22 % z = 5.5 cm

dE/dx= 8.5 %  = 7.9 mr B field: 0.4 T

p/p=1.7%(1+p2) z = 2.3 cm


World J/ and (2S) Samples (106)

Largest from BES






Phys. Rev. Lett. 91, 022001 (2003)

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II



acceptance weighted BW

+3 +5

-10 -25

M=1859 MeV/c2

G < 30 MeV/c2 (90% CL)






M(pp)-2mp (GeV)

3-body phase space



Phys. Rev. Lett. 95, 262001 (2005)

At BESII: Observation of X(1835) in

Statistical Significance 7.7 


The same origin as ppbar

mass threshold?

 a ppbar bound state?

The +- mass spectrum for  decaying into +- and  

observation of an anomalous enhancement near the threshold of mass spectrum at bes ii

Phys. Rev. Lett. 93, 112002 (2004)

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II


3-body phase space

For a S-wave BW fit: M = 2075 12  5 MeV

Γ = 90  35  9 MeV


Observation of  mass threshold structure X(1810) in J/   at BESII







Jpc favors 0++

Phys. Rev. Lett., 96 (2006) 162002

Possible theoretical interpretations:

glueball, hybrid, multiquark?

very broad 1 resonance x 1580 observed in k k mass spectrum in j k k 0 at besii
Very broad 1- - resonance X(1580) observed in K+K- mass spectrum in J/ K+K-0 at BESII



Phys. Rev. Lett. 97 (2006) 142002

So far the only reasonable interpretation is a multiquark state

due to its very broad width

at bes
σ at BES
  • BES II observed σ in J/  +-.
  • Pole position from PWA:


at besii
κ at BESII
  • BESII firmly established neutral  in J/  K*0K  KK in 2006:
  • PWA result

Pole position:



Observation of charged  at BESII

  • New result: Charged  observed at BESII in
  • Different parameterizations are tried in PWA.

The pole position:

BESII Preliminary

K*(1410), K*(1430)

consistent with neutral 

M(K0) GeV/c2


qcd studies at low energies
QCD studies at low energies


BESIII: < 2%


  • Understand where exactly pQCD becomes invalid
  • Precision measurement of as running
  • Precision measurement of R
  • input to
  • Related toaQED (s), prediction of higgs mass and g-2
  • A new measurement at BESII on R
    • Precision at ~ 3.5%
    • A new determination of s(s):

s(M2Z) = 0.1170.012

In good agreement with previous results

resonance parameter fit
Resonance parameter fit

Probability =31.8%

Phys. Lett. B660, (2008)315

Heavy charmonia parameters were fitted with the data between 3.7–5.0GeV, taking into accounts the phase angles, interference, energy-dependent width, etc.


Anomalous y(3770) lineshape

Black dots: data

Red dots: data subtracting J/y, y(3686) and continuum contribution

Green line: fit with one y(3770) hypothesis;

Red line: fit with two cross section

Blue line: fit with two amplitude

Check all lines !!!

PRL101 (2008) 102004

bepc ii storage ring large angle double ring
BEPC II Storage ring: Large angle, double-ring




Beam energy:

1.0-2 .3GeV


1×1033 cm-2s-1

Optimum energy:

1.89 GeV

Energy spread:

5.16 ×10-4

No. of bunches:


Bunch length:

1.5 cm

Total current:

0.91 A

BESIII detector



BESIII Commissioning and data taking milestones

Mar. 2008: first full cosmic-ray event

April 30, 2008: Move the BESIII to IP

July 18, 2008: First e+e- collision event in BESIII

Nov. 2008: ~ 14M y(2S) events collected

April 14, 2009 ~100M y(2S) events collected

May 30, 2009 42 pb-1 at continuum collected

July 28, 2009 ~200M J/y events collected

Peak Lumi. @ Nov. 2008:

1.2 1032cm-2s-1

Peak Lumi. @ May 2009:



Detector performance and calibration

●Layer 7

●Layer 22

Wire reso.

Design: 130 mm

dE/dx reso.: 5.80%


CsI(Tl) energy reso.

Design: 2.5%@ 1 GeV

Barrel TOF reso.: 78 ps

Design:80-90 ps


e1 transitions inclusive photon spectrum
E1 transitions: inclusive photon spectrum




c1,2 J/


BESIII preliminary

observation of h c e1 tagged y 2s p 0 h c h c gh c
Observation of hc: E1-tagged y(2S)p0hc,hcghc

background subtracted

BESIII preliminary

BESIII preliminary

N(hc)= 2540±261 c2/d.o.f = 39.5/41.0

Systematic errors under study

CLEO’s results (arXiv 0805.4599v1) :

M(hc)Inc= 3525.35±0.23±0.15 MeV

Br(y’p0hc)×Br(hcghc)Inc =(4.22±0.44±0.52) ×10-4 (G(hc) fixed at G(cc1) ~0.9MeV

CLEOc: Combined E1-photon-tagged spectrum and exclusive analysis

M(hc)avg= 3525.28±0.19±0.12 MeV

Br(y’p0hc)×Br(hcghc)avg =(4.19±0.32±0.45) ×10-4

(arXiv 0805.4599v1)

Select E1-photon to tag hc

A fit of D-Gaussian signal+ sideband bkg. yield:

M(hc)Inc = 3525.16±0.16±0.10 MeV

G(hc)Inc = 0.89±0.57±0.23 MeV (First measurement)

Br(y’p0hc)×Br(hcghc)Inc =(4.69±0.48(stat)) ×10-4 (G(hc) floated)

=(4.69±0.29(stat)) ×10-4 (G(hc) fixed at G(cc1))

observation of h c inclusive y 2s p 0 h c
Observation of hc : Inclusive y(2S)p0hc

BESIII preliminary

BESIII preliminary

Inclusive p0 recoil

mass spectrum

background subtracted

Systematic errors under study

Select inclusive p0

A fit of D-Gaussian signal + 4th Poly. bkg yield

N(hc) = 9233±935, c2/d.o.f = 38.8/38.0

Combined inclusive and E1-photon-tagged spectrum

Br(y’p0hc) =(8.42±1.29(stat)) ×10-4 (First measurement)

Br(hcghc) =(55.7±6.3(stat))% (First measurement)


study of 2s 0 0 0
Study of (2S)→ 00 , ( → ,0 → )


Nc016645±175 Nc24149±82


Nc01541±56 Nc2291±23

  • Interesting channels for glueball searches
  • Based on 110M y(2S)
  • BK study from 100M inclusive MC sample and 42pb-1 continuum sample
  • Unbinned Maximum Likelihood fit:
    • Signal: PDF from MC signal
    • Background: 2nd order Poly.

CLEO-c arxiv:0811.0586

confirmation of the besii observation pp threshold enhancement in j y decays
Confirmation of the BESII observation: pp threshold enhancement in J/y decays

BES III preliminary


(2S)→ J/y


M(pp)-2mp (GeV)

+3 +5

-10 -25

M=1864.6 ± 5.3MeV/c2

G < 33 MeV/c2 (90% CL)

M=1859 MeV/c2

G < 30 MeV/c2 (90% CL)

PRL 91 (2003) 022001

confirmation of besii observation no pp threshold enhancement in y decays
Confirmation of BESII observation: No pp threshold enhancement in y’ decays

BES III preliminary



No significant narrow enhancement near threshold

(~2 if fitted with X(1860))

No enhancement in y’ decays

In fact, no enhancement in ψ’ ,ϒ(1S) decays and in the process of J/y wppbar show that FSI unlikely .

PRL 99 (2007) 011802

study of c cj vv v w f
Study of ccJ VV, V=w,f
  • Backgrounds from sideband & 100M MC events
  • Clear cc1 ff signal
  • to be understood

BESIII preliminary

Test QCD-based theory at ccJ decays

Puzzles for cc0  VV: no helicity suppress

cc1 ff, ww highly suppressed owing to symmetry of identical particles

cc1 fw OZI doubly suppressed

first observation of c c1 wf
First observation of cc1 wf

BESIII preliminary

Background from sideband & 100M MC events

Clear signal from cc1 w(p+p-p0/rp0)f(K+K-)

event statistics at besiii
Event statistics at BESIII

*CLEO took 10 nb D production cross section while we took 5 nb

precision measurement of ckm branching rations of charm mesons
Precision measurement of CKM:Branching rations of charm mesons
  • Vcd /Vcs: Leptonic and semi-leptonic decays
  • Vcb: Hadronic decays
  • Vtd /Vts: fD and fDs fromLeptonic decays
  • Vub: Form factors of semi-leptonic


  • Unitarity Test of CKM matrix
precision test of sm and search for new physics
Precision test of SMand Search for new Physics
  • DDbar mixing

DDbar mixing in SM ~ 10 –3 -10 –10

DDbar mixing sensitive to “new physics”

Our sensitivity : ~ 10-4

  • Lepton universality
  • CP violation
  • Rare decays

FCNC, Lepton no. violation, ...

qcd and hadron production
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.
r value measurement
R-value measurement

Errors on R will be

reduced to 2% from

current 6%

j decays are an ideal factory to search for and study light exotic hadrons
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.
one important physics goal of besiii
One Important Physics Goal of BESIII

With 1010 J/psi events, we hope to answer:

  • Whether glueballs exist or not?
    • Naively, we estimate in each exclusive decay mode:
    • If the eff. is about 20%, we would have 20000 events for each decay mode

 we should observe a relative narrow (width: 50~200MeV) glueball if it exists.

difficulties i
Difficulties (I)
  • Theoretically:
    • Predictions on glueball masses from LQCD may be unreliable due to quench approximation.
    • No predictions on the widths so far (even the order).
    • No prediction on the production rate (J/  G).
    • Mix with qqbar mesons or even with 4q, qqg mesons? (dirty?) What is the mixing mechanism from the first principle?
difficulties ii
Difficulties (II)
  • Experimentally:
    • Data sample is not big enough (it is not a problem for BESIII)
    • No good way modeling background at low energy, in many cases we have to study bck via data.
    • Interferences among mesons make the mass/Dalitz plots very complicated 
      • PWA is crucial for hadron spectroscopy at BESIII
      • But PWA may face many uncertainties.
about scalar glueball
About scalar glueball
  • Many scalar mesons in the mass range 1.4~1.8 GeV, where a scalar glueball is predicted to be. More studies will be performed at BESIII.
  • More theoretical studies are also needed:
    • Not only glueball mass, but also width
    • Decay patterns
    • Production rate in J/psi radiative decays
    • Mixing mechanism
2 glueball candidates
2++ glueball candidates
  • Lattice QCD predicts the 2++ glueball mass in the range of 2.2~2.4 GeV
  • (2230) was a candidate of 2++ glueball:
    • It was first observed at MARKIII in J/KK
    • It was observed at BES I in J/KK, , ppbar
    • It was not observed at DM2.
the situation at besii
The situation at BESII
  • The mass plots shows no evident (2230) peaks in J/KK, , ppbar, which is clearly different from BESI.
  • Careful PWA is needed to draw firm conclusion on its existence since it may be still needed in the PWA although no clear mass peak observed.
  • Difficult to draw firm conclusion at present. We hope to give a final answer at BESIII on (2230) .
other 2 glueball candidates
Other 2++ glueball candidates
  • No other obvious good candidates have been observed in J/psi radiative decays in the mass range predicted by LQCD.
  • What does it mean:
    • LQCD prediction might not be very reliable, or
    • BR(J/  G)xBR(Ghh) is small ( <10-4 ) so that we don’t have the sensitivity to observe it ( quite possible ), or,
    • The width of a glueball is very large ( ~1GeV, E.Klepmt ).
where to search for the 0 glueball
Where to search for the 0-+ glueball?
  • Lattice QCD predicts the 0-+glueball mass in the range of 2.3~2.6 GeV.
  • (1440) and X(1835) were suggested being possible candidates, but their masses are much lower than LQCD predictions.
no 0 glueball candidate observed in the mass range 2 3 2 6 gev
No 0-+ glueball candidate observed in the mass range 2.3~2.6 GeV
  • No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in
  • Again:
    • LQCD reliable?
    • Production rate could be very low.
    • Glueball width could be very large.
  • Physics at BES (tau-charm threshold) are very rich.
  • There are many exciting discoveries at BESII.
  • BESIII is operational since 2008:
    • Detector performance excellent, ready for physics
    • High quality data samples in hand
    • Analysis in progress, papers in a few months
  • With much more statistics of data sample and much improved detectors at BESIII, more exciting discoveries can be expected.
  • Some fundamental questions, such as the existence of glueballs, might be answered at BESIII with close collaboration with theorists.
prospects a bright future
Prospects: a bright future

To be decided in Nov.

L ~ 1035-36 cm-2s-1

Expand the life time of tau-charm colliders to > 50 years !

  • BESIII will resume data taking after summer shutdown, ~5 months until next summer
  • Possible plans:
    • 500-1000 M J/y events (2-4 months)
    • 500-1000 M y(2s) (2-4 months)
    • 2fb-1y(3770) (4 months)
    • Lineshape scan of y(3770) (2 weeks)
  • Future charm programs
    • LHCb at CERN(soon)
    • BELLE II at SuperB factory(~ 2014 )
    • PANDA at GSI(~ 2015)
  • New programs under discussion:
    • Frascati(super flavor factory)
    • Novosibirsk(super tau-charm factory)
    • Fermilab
      • TeV fixed target exp. ?
      • Ppbar exp. ?