Physics at BES

Shan JIN(for the BESIII Collaboration)

Institute of High Energy Physics (IHEP)

jins@mail.ihep.ac.cn

USTRON09, Poland September 12-16, 2009

Outline

Introduction of BES experiments and Physics at BES

Highlights at BESII

Status of BESIII and preliminary results

Future prospects at BESIII

Conclusion

3

Linac Storage Ring

BES BSRF

Beijing Electron Positron Collider (BEPC) at IHEP

BESI: 1989-1998

BESII: 1999-2004

L ~ 51030 /cm2s 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 31032/cm2s at (3770) designed L: 1033/cm2s

注入器长 202 米

储存环的周长为 240.4米

对撞能量 2-5GeV 物理目标

北京正负电子对撞机（ BEPC ）示意图

Why tau-charm physics is interesting

Abundant resonances(J/ family, huge Xsections) Tau-charm threshold production(in pairs tagging backg

round free, no fragmentation, kinematic constrains, quantum coherence,…)

Charm quark: A bridge between pQCD and non-pQCD A ruler for LQCD J/decayGluon rich environment Flavor physics Complementary to LHC: virtual vs real A broad spectrum & efficient machine:

in the past in the era of LHCin the future

bsd

tcu

e

e

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 hadr

ons ?• pQCD: 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

DDhep-ex/0809.1869

Light hadron spectroscopy Motivation:

• Establish spectrum of light hadrons• Search for non-conventional hadron

s• Understand how hadrons are forme

d • Study chiral symmetry in QCD

Why at a tau-charm collider ?• Gluon rich• Larger phase space than at higher e

nergies • Clean environment, JPC filter

Glueball spectrum from LQCDGlueball spectrum from LQCD

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

Many results in BESII: ~ 50 publicationsMuch more from BESIII:100 statistics, 10 resolution

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.

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 What to study ?

• Production, decays, transition, spectrum

For what ?• A lab for pQCD and n

on-pQCD• Calibrate LQCD• How quarks form a ha

dron ?

Why at a tau-charm collider ?• A clean environment • Tagging possible • Abundantly produced

Examples of interesting/long standing issues: • puzzle• Missing states ?• Mixing states ?• New states above open charm thre.(X,Y,Z,…)

Highlights at BESII

BESII

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)

J/ (2S)

0

10

20

30

40

50

60

MarkI I I DM2 BES I BES I I

0

2

4

6

8

10

12

14

MKI MKII MKIII CBAL BESI BESII

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

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

J/pp

M(pp)-2mp (GeV)

0 0.1 0.2 0.3

3-body phase space acceptance

2/dof=56/56

acceptance weighted BW +3 +5

10 25

pp

BES II

Phys. Rev. Lett. 91, 022001 (2003)   

At BESII: Observation of X(1835) in

The +- mass spectrum for decaying into +- and

Statistical Significance 7.7

JBESII

J

MeVm 7.21.67.1833

MeV7.73.207.67

Phys. Rev. Lett. 95, 262001 (2005)   

The same origin as ppbar mass threshold? a ppbar bound state?

BES II

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

BES II pKJ /

3-body phase space

For a S-wave BW fit: M = 2075 12 5 MeV Γ = 90 35 9 MeV

Phys. Rev. Lett. 93, 112002 (2004)   

M2()

M2 (

) BackgroundX(1810)

Observation of mass threshold structure X(1810) in J/ at BESII

M()

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

2

21926

MeV/c 2820105

MeV/c 181812

M

Jpc favors 0++

Possible theoretical interpretations: glueball, hybrid, multiquark?

BES II

)1580(X

Background

0)1580(X

Very broad 1- - resonance X(1580) observed in K+K- mass spectrum in J/ K+K-0 at BESII

1

MeV/c )818(2

)1576(2

264 22133 23

98 4991 55

PCJ

iiM

Phys. Rev. Lett. 97 (2006) 142002

So far the only reasonable interpretation is a multiquark statedue to its very broad width

BES II

σ at BES BES II observed σ in J/ +-.

Pole position from PWA:

BES II

M

MeVi )42252()39541(

κ at BESII

BESII firmly established neutral in J/ K*0K KK in 2006:

PWA result

Pole position:

BES II

24872

8173 MeV/c )45309()30841(

i

Observation of charged at BESII

New result: Charged observed at BESII in

Different parameterizations are tried in PWA.

The pole position:

0*/ KKKJ s

M(K0) GeV/c2

BESII Preliminary

K*(1410), K*(1430)26430

1428 MeV/c )101288()51841(

i

consistent with neutral

QCD studies at low energies Understand where exactly pQCD becomes invalid Precision measurement of s running

Precision measurement of R input to Related to QED (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) = 0.1170.012

?

Phys.Lett.B677,(2009)239

Ecm(GeV)

L(pb-1) R s(S)

2.60 1.222 2.180.020.08

3.07 2.291 2.130.020.07

3.65 6.485 2.140.010.07

In good agreement with previous results

BESIII: < 2%

Resonance parameter fit Heavy charmonia parameters were fitted with the data betwee

n 3.7–5.0GeV, taking into accounts the phase angles, interference, energy-dependent width, etc.

Phys. Lett. B660, (2008)315

Probability =31.8%

PRL101 (2008) 102004

Black dots: dataRed dots: data subtracting J/and continuum contribution

Green line: fit with one (3770) hypothesis;Red line: fit with two cross sectionBlue line: fit with two amplitude

Anomalous (3770) lineshape

Check all lines !!!

quantity Two AM Two AM One AM Y(3770)+G(3900)

2 125/103 112/102 182/106 170/104

(3686) (MeV) 3685.50.00.5 3685.50.00.5 3685.50.00.5 3685.50.00.5

M1 (MeV) 3765.02.40.5 3762.611.80.5 3773.30.50.5 3774.40.50.5

M2 (MeV) 3770.50.60.5 3781.01.30.5 3943.0(Fixed)

Status of BESIII and preliminary results

BEPC II Storage ringBEPC II Storage ring:: Large angle, double-ring

RFRF SR

IP

Beam energy: 1.0-2 .3GeVLuminosity: 1×1033 cm-2s-1

Optimum energy: 1.89 GeVEnergy spread: 5.16 ×10-4

No. of bunches: 93Bunch length: 1.5 cmTotal current: 0.91 A

BESIII detector

BESIII Commissioning and data taking milestones Mar. 2008: first full cosmic-ray eventApril 30, 2008: Move the BESIII to IPJuly 18, 2008: First e+e- collision event in BESIIINov. 2008: ~ 14M (2S) events collectedApril 14, 2009 ~100M (2S) events collectedMay 30, 2009 42 pb-1 at continuum collectedJuly 28, 2009 ~200M J/ events collected

Peak Lumi. @ Nov. 2008: 1.2 1032cm-2s-1 Peak Lumi. @ May 2009: 3.21032cm-2s-1

Detector performance and calibration

● Layer 7● Layer 22

Wire reso. Design: 130 m

dE/dx reso.: 5.80%Design ： 6-8%

CsI(Tl) energy reso. Design: 2.5%@ 1 GeV

Barrel TOF reso.: 78 psDesign ： 80-90 ps

Bhabha

E1 transitions: inclusive photon spectrum

c2c1

co

c1,2 J/

c

BESIII preliminary

Observation of hc: E1-tagged (2S)0hc,hcc

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

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

Br(’hc )×Br(hcc )Inc =(4.69±0.48(stat)) ×10-4 ((hc) floated) =(4.69±0.29(stat)) ×10-4 ((hc) fixed at (c1))

background subtracted

Systematic errors under study

CLEO’s results (arXiv 0805.4599v1) : M(hc)Inc= 3525.35±0.23±0.15 MeV Br(’hc )×Br(hchc )Inc =(4.22±0.44±0.52) ×10-4 ((hc) fixed at (c1) ~0.9MeVCLEOc: Combined E1-photon-tagged spectrum and exclusive analysis M(hc)avg= 3525.28±0.19±0.12 MeV Br(’hc )×Br(hchc )avg =(4.19±0.32±0.45) ×10-4

BESIII preliminary

BESIII preliminary

N(hc)= 2540±261 2/d.o.f = 39.5/41.0

(arXiv 0805.4599v1)

Observation of hc : Inclusive (2S)0hc

Select inclusive 0

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

N(hc) = 9233±935, 2/d.o.f = 38.8/38.0

Combined inclusive and E1-photon-tagged spectrum

Br(’hc ) =(8.42±1.29(stat)) ×10-4 (First measurement)

Br(hcc) =(55.7±6.3(stat))% (First measurement)

31

background subtracted

Inclusive recoil mass spectrum

Systematic errors under study

BESIII preliminary

BESIII preliminary

BR (10-3) c0 c2

00 BESIII 3.25±0.03(stat) 0.86±0.02(stat)

PDG 2. 43±0.20 0.71±0.08

CLEO-c 2.94±0.07±0.35 0.68±0.03±0.08

BESIII 3.1±0.1(stat) 0.59±0.05(stat)

PDG 2.4±0.4 <0.5

CLEO-c 3.18±0.13±0.35 0.51±0.05±0.06

CLEO-c arxiv:0811.0586

Study of (2S)→ 00 , → , 0 → Interesting channels for glueball searches

Based on 110M (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.

2S)00

Nc0 16645±175 Nc2 4149±82

2S)

Nc0 1541±56 Nc2 291±23

Confirmation of the BESII observation: pp threshold enhancement in J/decays

PRL 91 (2003) 022001

/J pp

BES III preliminary

(2S)→ J/

M=1864.6 ± 5.3MeV/c2

< 33 MeV/c2 (90% CL)

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

+3 +510 25

0.3

/J pp BES II

M(pp)-2mp (GeV)

Confirmation of BESII observation: No pp threshold enhancement in ’ decays

No significant narrow enhancement near threshold(~2 if fitted with X(1860))

Mpp (GeV)

BES III preliminary

PRL 99 (2007) 011802

BES II

No enhancement in ’ decays

pp pp

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

0c1c

2c

Study of cJ VV, V= Test QCD-based theory at cJ decays

Puzzles for c0 VV: no helicity suppress

c1 highly suppressed owing to symmetry of identical particles

c1 OZI doubly suppressed

BESIII preliminary

0c 1c 2c

c0 f or KKm K K c1 f or KKm K K c2 f or KKm K K

BESII results:

BR(10-

3)c0 c2

0.930.20 1.50.3

2.30.7 2.00.7

• Backgrounds from sideband & 100M MC events

• Clear c1 signal

• to be understood

(GeV)K K

m

(GeV)m

0

First observation of c1

Background from sideband & 100M MC events Clear signal from c1 (K+K-)

0c

1c2c

BESIII preliminary

Future prospects at BESIII

Event statistics at BESIII Physics

Channel

Energy

(GeV)

Luminosity

(1033 cm–2s –1)

Events/year

J/ 3.097 0.6 1.0×1010

3.67 1.0 1.2×107

’ 3.686 1.0 3.0 ×109

D 3.77 1.0 2.5×107

Ds 4.03 0.6 1.0×106

Ds 4.14 0.6 2.0×106

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

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

CKM matrix elements measurement

Current BESIII

Vub 25% 5%

Vcd 7% 1%

Vcs 16% 1%

Vcb 5% 3%

Vtd 36% 5%

Vts 39% 5%

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

R-value measurement pQCD and non-pQCD boundary Measurement of s at low energies Hadron production at J/’, and continium Multiplicity and other topology of hadron eve

nt BEC, correlations, form factors, resonance,

etc.

R-value measurement

Error on R (5)had (MZ

2)

5.9% 0.02761 ±0.00036

3% 0.02761 ±0.00030

2% 0.02761 ±0.00029

Errors on R will be reduced to 2% from current 6%

Prospects of glueball searches at BESIII

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

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.

510~)()/( hhGBRGJBR

310 210

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) 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 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

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.

BES-I (2230) Result

(2230)

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) .

00/ ss KKJ

KKJ /

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(Ghh) 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?

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 evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in

Again:• LQCD reliable?• Production rate could be v

ery low.• Glueball width could be ve

ry large.

...',

*,*,,/

KKKKJ

'M

)1835(X

Summary

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.

Thanks! 谢谢！

Prospects: a bright future BESIII will resume data taking after summer shutdo

wn, ~5 months until next summer Possible plans:

• 500-1000 M J/events (2-4 months)• 500-1000 M (2s) (2-4 months)• 2fb-1 (3770) (4 months)• Lineshape scan of (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. ?

To be decided in Nov.

L ~ 1035-36 cm-2s-1

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