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Overview of BESIII Experiment

Hai-Bo Li(Representing BESIII Collaboration)

Institute of High Energy Physics

Workshop on EIC Physics

July 27-30, 2013, Weihai, Shandong University, China

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Outline

• Introduction

• BESIII data sets

• Selected results from BESIII– Hadron spectroscopy (XYZ, light hadron spec.)– Charmonium physics– Charm physics

• Summary

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-charm: Main physics goals Hadron spectroscopy and test of QCD at low energy: Light meson and baryon Glueball: direct test of QCD at low energy Hybrid/exotics states/multiquark states/molecular states… Charmonium(-like) spectroscopy and decays / Charmed baryon decays

Precise test of the Standard Model: R values, tau leptonic decays, CKM matrix, lepton universality test… Decay constants, form factors (in D meson decays) Neutral D mixing

New physics searches at low energy ( tiny/forbidden in SM): Rare charmonium decays: weak decays, LFV, LNV, BNV … Rare charm and tau decays: FCNC, LFV, LNV, invisible decays Rare light meson decays: /// rare decays CP violation in tau and charm: tiny in SM CP violation in baryon /charmed baryon weak decays

Exotic physics: Light dark matter candidates, Dark photon, light Higgs boson(a0), New interactions…

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BESIII detector

LINAC

2004: started BEPCII/BESIII construction2008: test run2009 - now: BESIII physics run

Beijing Electron Positron Collider-II (BEPCII)

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BEPCII storage ringsBeam energy: 1.0-2.3 GeVDesign Luminosity: 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 ACircumference： 237m

Achieved luminosity: 0.7×1032 cm-2s-1@3770MeV

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Japan (1)Tokyo Univ.

US (6)Univ. of Hawaii

Univ. of WashingtonCarnegie Mellon Univ.

Univ. of Minnesota Univ. of Rochester

Univ. of Indiana

Europe (13)Germany: Univ. of Bochum,

Univ. of Giessen, GSI Univ. of Johannes Gutenberg

Helmholtz Ins. In MainzRussia: JINR Dubna; BINP Novosibirsk

Italy: Univ. of Torino ， Frascati Lab, Ferrara Univ.Netherland ： KVI/Univ. of Groningen

Sweden: Uppsala Univ. Turkey: Turkey Accelerator Center

China(29)IHEP, CCAST, GUCAS, Shandong Univ.,

Univ. of Sci. and Tech. of ChinaZhejiang Univ., Huangshan Coll.

Huazhong Normal Univ., Wuhan Univ.Zhengzhou Univ., Henan Normal Univ.

Peking Univ., Tsinghua Univ. ,Zhongshan Univ.,Nankai Univ., Beihang Univ.

Shanxi Univ., Sichuan Univ., Univ. of South ChinaHunan Univ., Liaoning Univ.

Nanjing Univ., Nanjing Normal Univ.Guangxi Normal Univ., Guangxi Univ.Suzhou Univ., Hangzhou Normal Univ.

Lanzhou Univ., Henan Sci. and Tech. Univ.

Korea (1)Seoul Nat. Univ.

Pakistan (2)Univ. of Punjab

COMSAT CIIT

~350 members52 institutions from 11 countries

The BESIII Collaboration

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BESIII data taking status & plan

Previous data

BESIII present & future Goal

J/ BESII: 58M 1.2 B 20* BESII 10 B

’ CLEO: 28 M 0.5 B 20* CLEOc 3B

” CLEO: 0.8/fb 2.9/fb 3.5*CLEOc 20/fb

4040/4160/4260 /4360 MeV

CLEO: 0.6/fb @ 4160)

2011: 0.4/fb @ 4040)2013 ： 2/fb@4260, 0.5/fb 4360 Data for lineshape

5-10/fb

R scan BESII 2012: R @2.23,2.4,2.8,3.4GeV 25/pb tau2013-2014: high mass resonances? R measurement ?

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BESIII collected 3.3/fb for XYZ study (2012-2013)

4010

4190

4210

4220

4230

4245

4260

4360

4390

4420

4310

9

3810 39

00

4090

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Charmonium spectroscopy• Charmonium states below open charm threshold are all observed

Above open charm threshold:

• many expected states not observed• many unexpected charmoniumlike states observed

from Ryan Mitchell

X(3872)X(3915)X(4160)X(4350)

XYZ(3940)

Y(4008)

Y(4140)

Y(4260)

Y(4360)

Y(4660)

Y(4008)

Y(4140)

Y(4260)

Y(4360)

Y(4660)

Z(4430)Z(4250)Z(4050)Z(3900)

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Y(4260)

PRD86, 051102454/fb

PRL95, 142001 273/fb PRL110, 252002

967/fb

e+e- ISR(J/)

4260

(e+e- hadrons)(e+e- +-)

BESII

J/J/++

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Y(4360) and Y(4660)

PRL98, 212001298/fb

arXiv: 1211.6271, CHARM2012

e+e- ISR(’)++

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Select e+e +J/ at 4.26 GeV

BESIII: PRL110, 252001 (2013)525/pb @4.26 GeV

59528J/

e+e

88233J/ +

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Cross section of e+e +J/

BaBar: PRD86, 051102 (2012)

Belle: 1304.0121

BESIII: (e+e- +-J/) = (62.91.93.7) pbAgree with BaBar & Belle!Best precision!

BESIII: PRL110, 252001

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BESIIISignificance >8

• M = 3899.03.64.9 MeV• = 461020 MeV• 307 48 events

BESIII: PRL110, 252001 (2013)

Observation of Zc(3900) at BESIII

The mass position is 24 MeV away from DD* threshold! A Partial wave analysis is on going!

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CLEOc data at 4.17 GeV arXiv: 1304.3036

• M = 388551 MeV• = 34124 MeV• 81 20 events• 6.1

BELLE ： e+e- +-J/ from ISRBelle: PRL 110, 252002(2013)

• M = 3894.56.64.5 MeV• = 632426 MeV• 159 49 events• >5.2

586/pb

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Zc: charged charmoniumlike states• Find a clear signature for exotic state!

• Decays to charmonium thus has a cc pair!

• With electric charge thus has two more light quarks!

Nquark 4 !

• DD* molecule? Tetraquark state? Cusp? Threshold effect?

• Do searches in πhc(1P), πψ(2S), πcJ, …

• BESIII: e+e- π+exotics, +exotics, …

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Observation of e+e- +-hc(1P)• 827 pb-1 at Ecm=4.26 GeV; 544 pb-1 at Ecm=4.36 GeV

• hcc, c hadrons [16 exclusive decay modes] pp, +-K+K-, +-pp, 2(K+K-), 2(+-), 3(+-) 2(+-)K+K-, KS

0K+-+c.c., KS0K+-+-+c.c., K+K-0

pp0, K+K-, +-, +-00, 2(+-), 2(+-0)

Ecm=4.26 GeV Ecm=4.36 GeV

LP2013, C. Z. Yuan

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N(hc)=41628 Lum=827/pbB= 41.02.87.4 pb

N(hc)=35725 Lum=544/pbB= 52.33.79.2 pb

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Ecm=4.26 GeV Ecm=4.36 GeV

Observation of e+e +hc(1P)

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Puzzle of “Y(4260)”

)%6.70.66())1()4260((

))1()4260((

SY

PhY c

S(hc(1P)) = 0 S(J/) = 1

Mechanism of +hc production is exotic! Study of the substructure is motivated !

Spin-flip No spin-flip

Process with spin-flip of heavy quark is not suppressed.

Assuming the +hc(1P) is from Y(4260) decay:

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Observation of Zc(4020) in e+e +hc(1P)Ecm=4.26 GeV Ecm=4.36 GeV

Simultaneous fit to 4.26/4.36 GeV data and 16 c decay modes: 6.4

M(Zc(4020)) = 4021.81.02.5 MeV(Zc(4020)) = 5.73.41.1 MeV

N= 6419

N= 5617

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e+e (D*D*)++c.c. @4.26 GeV

• 827 pb-1 data at Ecm=4.26 GeV• Tag a D+ and a bachelor , reconstruct one 0 to

suppress the background.

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Remove DD, DD*, D*D*, DsDs, …

e+e (D*D*)++c.c. @4.26 GeV

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Observation of Zc(4025) in e+e (D*D*)++c.c.

Fit to recoil mass yields 40147 Zc(4025) events. >10 M(Zc(4025)) = 4026.32.63.7 MeV; (Zc(4025)) = 24.85.77.7 MeV

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Zc(4020)=Zc(4025)?

• M(4020) = 4021.81.02.5 MeV• M(4025) = 4026.32.63.7 MeV• (4020) = 5.73.41.1 MeV• (4025) = 24.85.77.7 MeV

Close to D*D* threshold=4017 MeVMass consistent with each other but width

~2 difference

Interference with other amplitudes may change the results

Coupling toD*D* is much larger than to hc if they are the same state

Will fit with Flatte formula

High stat. dataare needed!

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What next at BESIII? Precise resonant parameters

Spin-parity

More decay modes [, c, open charm,…]

Production mechanisms, production rates

Test various theoretical models

Neutral partners of Zc and Zc Excited Zc, Zc states? ZcsKJ/ states?

Other XYZ states?…

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X(3872) at BESIII

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Observation of e+e X(3872)+J/

Clear ISR ’ signal for data validationX(3872) signal at around 4.23-4.26 GeV

Ecm=4.01 GeV Ecm=4.23 GeV

Ecm=4.26 GeV Ecm=4.36 GeV

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Observation of e+e X(3872)

ISR ’ signal is used for rate, mass, and mass resolution calibration.N(’)=1242 ; Mass=3685.960.05 MeV; M=1.84 0.06 MeV

N(X(3872))=15.03.9 5.3 M(X(3872)) = 3872.10.80.3 MeV [PDG: 3871.68 0.17 MeV]

Sum of all energy points

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Observation of e+eX(3872)

30LP2013, C. Z. Yuan

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Light hadron spectroscopy

-- from charmonium decays

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pp enhancement at threshold

Observed at BESII in 2003 M=1859+3

-10+5

-25 MeV Width < 30 MeV (90% CL) Agree with spin zero expectation

• Possibilities Conventional meson? pp bound state/ multiquark/

glueball/ … Phys. Rev. Lett., 91, 022001

pp/J

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Confirmed by CLEOc and BESIII

pγpJ/ψ J/ψ/ππψ'

BESIII-

CPC 34, 421 (2010)

fit with one resonance as BES did:pγpJ/ψ,J/'

CLEOc

M=1861 +6 -13

+7-26 MeV/c2

< 38 MeV/c2 (90% CL)

PRD 82, 092002 (2010)

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55.10.5

4.01.1

221013

21817

105

PC

10))model(3.2.)syst(.)stat(0.9()ppX(Br)X/J(Br

.)L.C90@c/MeV60(c/MeV )model(4.)syst(.)stat(3913

c/MeV )model(19.)syst(.)stat(1832M

0J

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PWA of J/pp @ BESIIIf0(2100) / f2(1910) fixed to PDG. Sig. of X(ppbar) >>30

BESIII: PRL 108, 112003 (2012)

Different FSI models Model dependent uncertainty

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Mpp (GeV)

No significant narrow threshold enhancement observed here:

(1S ) pp@CLEO

ψ γpp@BESII

J / pp@BESII

PRD 73 (2006) 032001

PRL 99 (2007) 011802

EPJC 53 (2008) 15

ψ γpp@BESIII @CLEOcPRD 82, 092002 (2010)

PRL 108, 112003 (2012)

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BESII: PRL 95,262001(2005)

Theoretical interpretation: pp bound state, excitation ….η Are X(pp) and X(1835) from the same source?

Statistical Significance ~ 6 Statistical Significance ~ 5.1

X(1835) in +

M=1833.7±6.1(stat)±2.7(syst)MeV=67.7±20.3(stat)±7.7(syst)MeV

'

'

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Fit with four resonances (acceptance weighted BW gaussian) Three background components:

① Contribution from non-’ events estimated by ’ mass sideband② Contribution from with re-weighting

method③ Contribution from “PS background”

Red line: estimated contribution of ①+ ②Black line: total background

X(1835) in J at BESIIIBESIII: PRL 108 (2011)112003

)'('/ 0 J

mmmmxamxamxxf bkg 02/5

012/3

002/1

0 ,)()()()(

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• With bin-by-bin mass spectrum fit, we can obtain background-subtracted, acceptance-corrected angular distribution

• Consistent with the expectation for a pseudoscalar, other assumptions are not excluded.

The angular distribution of the X(1835)BESIII: PRL 108 (2011)112003

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Why are X(2120) and X(2370) interesting?PRD73,014516(2006) Y.Chen et al First time in J/ radiative decays

resonant structures are observed in the 2.4 GeV/c2 region.

it is interesting since:

• LQCD predicts the lowest lying 0-+ glueball: around 2.4 GeV/c2.

• J/-->' decay is a good channel for finding 0-+ glueballs.

Nature of X(2120)/X(2370)

pseudoscalar glueball ?

/ excited states?

……

PRD82,074026,2010 J.F. Liu, G.J. Ding and M.L.YanPRD83:114007,2011 J.S. Yu, Z.-F. Sun, X. Liu, Q. zhao and more…

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X(18??) near the threshold position of proton-antiproton

Observations at BESIII with 225M J/ decays: ★ J/ (3( )) X(1840) arXiV:1305.5333○ J/ () X(1870) PRL107, 182001

▲ J/ (’) X(1835) PRL106, 072002 ■ J/ (ppbar) X(pp) PRL108,112003

┼ J/ () X(1810) PRD 87, 032008

arXiv:1305.5333Submitted to PRL

Are they the same particle? It is crucial to identify these Observations.

X(1840): J/ 3( )

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PWA in J/

• f0(1710) and f0(2100) are dominant scalars

• f0(1500) exists (8.2σ)

• f2’(1525) is the dominant tensor

• f2(2340) exists (7.6)

• No evidence for fJ(2220)

Phys. Rev. D. 87, 092009 (2013) 

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Decay rate of pure glueball from LQCD

BR(J/ G(0++)) = 3.8(9)103

Pure scalar-glueball rate in J/ radiative decays: Long-Cheng Gui et al. PRL 110 (2013) 021601

f0(1710)

Pure Tensor-glueball rate in J/ radiative decays:

BR(J/ G(2++)) = 1.1(2)102Yi-Bo Yang et al. arXiv: 1304.3807 Submitted to PRL Large decay rate is predicted!

Need more experimental information!

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Study of J/f0(980)0, f0(980)

f0(980)+f1/3.7

f1/1.2

f0(980)00

(1440) (1440)

BESIII: PRL 108 (2012) 182001

First observation of(1405)f0(980)0

(isospin violated decays)and J/f0(980)0

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Very narrow f0(980) – much narrower than PDG value!

Possible explanation: J.J.Wu et al, PRL 108, 081803(2012) effect of Triangle Singularity!

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4.2)%(17.9 ))980(a)1405((BR

))980(f)1405((BR

0

00

Large isospin breaking: (1440)f0(980)0 BESIII: PRL 108 (2012) 182001

In general, magnitude of isospin violation in strong decay should be less than 1% or at 0.1% level. For example:

%9.0)'(BR

)'(BR ,

|P|

|P|102.0

)/J'(BR

)/J'(BR 0

3

32

0

However:

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3 in J/

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More results on / physics(1) Measurement of -> + e+e and ++.

Phys.Rev. D87 (2013) 092011 [arXiv:1303.7360 [hep-ex]].

(2) Search for and + e +c.c. decays in J/ and .

Phys.Rev. D87 (2013) 032006

(3) Search for and Invisible Decays in J/ and . Phys.Rev. D87 (2013) 012009

(4) Search for CP and P violating pseudoscalar decays into . Phys.Rev. D84 (2011) 032006

(5) Measurement of the Matrix Element for the Decay . Phys.Rev. D83 (2011) 012003.

On going analyses: First observation +-+First observation of 0

First observation of e+e, 0e+e-Study of ’ + …

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N* resonances in decays0ppbar

Phys.Rev.Lett. 110 (2013) 022001

Two new baryonic excited states are observed !

J/ (’) decays offer an window to search for the missing baryon resonances. Many results are on going now at BESIII.

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Charmonium states’, hc(1P1), c(1S), c(2S)

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hc(1P1) state • Spin singlet P wave (S=0, L=1)• Potential model: if non-zero P-wave spin-spin interaction:

DMhf(1P) = M(hc) - <m(1 3PJ)> ≠0 where <m(1 3PJ)>= [(M(c0)+3M(c1)+5M(c2)]/9

•The hc(1P1) state was observed by CLEOc in 2005.

Theoretical prediction:

BF((2S)0hc) = (0.4-1.3)×10-4

BF(hcc) =48% (NRQCD)BF(hcc) =88% (PQCD) Kuang, PR D65 094024 (2002)

BF(hcc) =38% Godfrey and Rosner, PR D66 014012(2002)

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hc from inclusive (2S)0hc @BESIII

• Select inclusive 0

Br((2S)0hc) = (8.4 ± 1.3 ± 1.0) ×10-4

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backgroundsubtracted

BESIIIPRL 104,

132002 (2010)

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hc from E1-tagged (2S)0hc,hcc @BESIII

Select E1-photon to tag hc

M(hc) = 3525.40 ± 0.13 ± 0.18 MeV/c2

(hc) = 0.73 ± 0.45 ± 0.28 MeV/c2 (< 1.44 MeV/c2 @ 90% CL)

Br(ψ(2S)π0hc )×Br(hcc ) = (4.58 ± 0.40 ± 0.50) ×10-4

BESIIIPRL 104, 132002 (2010)

backgroundsubtracted

Combined inclusive and E1-photon-tagged spectrumBr(hcc) = (54.3 ± 6.7 ± 5.2) %

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’ 0hc, hcc , c exclusive decays

Simultaneous fit to 0 recoiling mass2/d.o.f. = 32/46Mass = 3525.31±0.11±0.14 MeV/c2

Width = 0.70±0.28±0.22 MeV/c2

CLEOc exclusive results Mass =3525.21±0.27±0.14 MeV/c2

evts. =136±14

Consistent with BESIII inclusive results

Mass = 3525.40±0.13±0.18 MeV/c2

Width = 0.73±0.45±0.28 MeV < 1.44 MeV (90% C. L. )

Summed distribution

832±35 evts.

BESIII: PRL 104 132002 (2010)CLEOc: PRL 101 182003 (2008)

BESIII: PRD 86, 092009 (2012)

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BESIII: PRL 104 132002 (2010) CLEOc: PRL 101 182003 (2008)

Mass : 3525.40±0.13±0.18 MeV/c2 Mass: 3525.28±0.19±0.12 MeVWidth: 0.73±0.45±0.28 MeV Width: fixed to 0.9 MeV <1.44 MeV @90%

Hyperfine mass splitting : DMhf(1P)= M(hc ) - <m(1 3PJ )>

BESIII: 0.10±0.13±0.18 MeV/c2

CLEOc: 0.02±0.19±0.13 MeV/c2

hc parameters

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c(1S)• The lowest lying S-wave spin singlet charmonium, discovered in 1980 by MarkII.

Properties not well known.• J/ radiative transition: M ~ 2978.0MeV/c2, ~ 10MeV process: M = 2983.1±1.0 MeV/c2, = 31.3±1.9 MeV• CLEOc found the distortion of the c line shape in ’ decays.

• hyperfine splitting M(J/)-M(c(1S)) is the important exp. input to test LQCD, but is dominated by error on M(c(1S)).

Mass width

C.L.<0.0001C.L.=0.0014

cc

pp, B decays (1S, 2S)c

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56

Asymmetric lineshape in J/ decay Symmetric lineshape in production

Symmetric c lineshape from 0hc, hcc

BESIIIPRD 86, 092009 (2012)

BESIIIPRD 86, 092009 (2012)

Background subtracted

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Possible interference has been taken into account

KsK KK0

KsK3 2K20 3()

C resonance parameters from C at BESIII

mass: 2984.30.6stat0.6sys MeV/c2

width: 32.01.2stat1.0sys MeV

PRL 108 (2012) 222002

Phys.Rev.Lett. 108 (2012) 222002

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Comparison of the mass and width for c(1S)

LQCD McNeileQWG 2011• The most precise measurement

• Better agreement with LQCD calculation.

Mass = 2984.3±0.6±0.6 MeV/c2

Width = 32.0±1.2±1.0 MeV

Hyperfine splitting: M(1S) = 112.6 ± 0.8 MeV

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• Crystal Ball’s “first observation” of ' X never been confirmed PRL 48 70 (1982)

• Observed in different production mechanisms• BKc(2S) • c (2S)KK• double charmonium production

• M1 transition ’c(2S) CLEOc found no signals in 25M ’. BF(’c(2S)) < 7.6×10-4 CLEOc: PRD 81 052002 (2010)

c (2S)

Belle: PRL 89 102001 (2002), NPPS.184 220 (2008), PRL 98 082001(2007)CLEOc: PRL 92 142001 (2004) BaBar: PRL 92 142002 (2004); PR D72 031101(2005), PR D84 012004 (2011)

Experimental challenge : detect photons of 50 MeV

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First observation of c(2S)@BESIII

• Observed signal in KsK+-+c.c. ， found evidence in K+K-0

• First measured Br(‘ c(2S))=(6.8±1.1±4.5) ×10-4

Potential model expectation: (0.1-6.2)10-4 PRL 89 162002 (2002) CLEOc: <7.6×10-4 PRD 81 052002 (2010)

Statistical significance >10 BESIII: PRL109, 042003 (2012)

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Charm physics at BESIII

Advantage of open charm at thresholde+e colliders@threshold:

Good for charm flavor physics: • Threshold production: clean • Known initial energy and quantum numbers • Both D and Dbar fully reconstructed (double tag) • Absolute measurements

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Pure leptonic decays

• All quantities are well measured except fD.• Use world average |Vcd| to extract fD

• Compare fD with LQCD for the validation of LQCD

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D+ Leptonic Decays

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D+ Leptonic Decays – Comparisons

G. Rong CHARM2012

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Semileptonic D decay Decay rate depends on kinematics and VCKM

Form factor encapsulates QCD bound-state effects Consider Pseudoscalar final states: K, π

Precise measurement of |Vcx|2f+(q2), get Vcx from CKMunitarity to extract form factor as test of Lattice QCD-

or reverse the logic and test of CKM unitarity.

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One third of total data@(3770)

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One third of total data@(3770)

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Summary

70

• BEPCII peak Luminosity of 0.7x1033 achieved.• Lots of progress on hadron spectroscopy • BESIII starts study of XYZ particles • First confirmed exotic state with at least four

quarks Zc(3900) • Observation of Zc’(4020) and Zc’(4025) • BESIII is in her golden age, nearly 60 papers have

been published since 2009 • More results will come soon, stay tuned!

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Thank you!