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Study of New Hadron Spectroscopy at BESIII

Liu Fang (IHEP)for BESIII Collaboration

The 9th National Workshop for Heavy Flavors and CP Violation2011.10.12-10.16

Hangzhou, Zhejiang, China

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OUTLINE

Introduction Latest results on new hadron spectroscopy

pp mass threshold enhancement in J/ and ’ radiative decaysConfirmation of X(1835) and observation of two new structures Observation X(1870) in J/(+-)

Summary

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Satellite view of BEPCII /BESIII

BESIII detector

LINAC

2004: start BEPCII construction2008: test run of BEPCII 2009-now: BECPII/BESIII data taking

South

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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

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BES Detector

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Data samples

• So far BESIII has collected :– 2009: 225 Million J/(4 BESII)

– 2009: 106 Million ’ (4 CLEOC)

– 2010-11: 2.9 fb1 (3770)

(3.5 CLEO-c 0.818fb1)

- May 2011: 0.5fb1 @4010 MeV (one month) for Ds and XYZ spectroscopy

• BESIII will also collect:– more J/, ’, (3770)– data at higher energies （ for XY

Z searches, R scan and Ds physics ）

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QCD allows different type of hadrons:

Light hadron

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Observation of pp mass threshold enhancement

/J pp

J / ,J / pp

@BESIII

@BESIII

pp @BESIII

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Observation of mass threshold enhancement @ BESII

Mpp-2mp (GeV)0 0.1 0.2 0.3

J / pp

theoretical speculation: bound state (baryonium) FSI effect ……

pp

BESIIX(1860)

3-body phase space

acceptance

pp

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

+3 +510 25

PRL 91 (2003) 022001

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No significant signal of X(1860) near threshold found(only 2 significance)

Mpp (GeV)

(1S ) pp@CLEO

pp@ BESII

J / pp@BESII

Several non-observations

PRD 73 (2006) 032001

EPJ C53 (2008) 15

PRL 99 (2007) 011802

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J / ,J / pp

Chinese Physics C 34, 421 (2010)

M=1861 +6 -13

+7-26 MeV/c2

< 38 MeV/c2 (90% CL)

0 0.1 0.2 0.3

J / pp

BESII

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

+3 +510 25

PRL 91 (2003) 022001

Observation of pp mass threshold enhancementat BESIII

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Evident narrow ppbar mass threshold enhancement

X(pp)

ηc

Partial Wave Analysis (PWA):• Concentrate on dealing with the mass threshold structure, especi

ally to determine the JPC (M(pp)<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).

pp

PWA on the pp mass threshold structure in

/J p p BESIII

Preliminary results

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PWA results and projections in /J p p Preliminary results

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Measurement for X(1860)

• 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):

>6.8σ better than other Jpc assignments.pc

19 217

11 2 233

1.5 55.1

J 0

M 1832 5(stat) (syst) 19 MeV/c

13 20(stat) (syst) 4(mod)MeV/c or 48MeV/c @ 90% . .

( / ( )) ( ( ) ) (9.0 0.7 (stat) (syst) 2.3 mod ) 10

C L

B J X pp B X pp pp

(mod)

（ ）

Preliminary results

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χ cJ

ηc

Obviously different line shape of ppbar mass spectrum near threshold from that in J/ψ decays

PWA Projection:

PWA results:• Significance of X(pp) is larger than 6.9σ .• The production ratio R:

• It is suppressed compared with “12% rule”.

first measurement

PWA on the pp mass threshold structure in pp

BESIII

+0.72-3.83= (5.08 0.5

( (

6(

))R

( / (

stat) (syst) 0.12(mod)

)

)%

)

B X pp

B J X pp

Preliminary results

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Confirmation of X(1835) in and observation of two new structures

at BESIII

J

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X(1835) at BESII

PRL 95,262001(2005)

  (Stat. sig. ~ 7.7 ) :

  1833.7 6.1( ) 2.7( )

67.7 20.3(stat) 7.7(syst)MeV

BESII result

M stat syst MeV

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 J/@BESII

Need to confirm X(1835) with BESIII ~225M J/ data !!!

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Mass spectrum of

X(1835) and c are evident.

Two additional structures are observed at M~2.1GeV and 2.3GeV

There maybe some f1(1510).

BES III

Combination for to +- and

BES III

X(2120)X(2370)

X(1835)

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Fitting with four resonances (acceptance weighted BW gauss) Three background components:

① Contribution from non-’ events estimated by ’ mass sideband

② Contribution from with re-weighting method

③ Contribution from “PS background”

Fitting for the combined mass spectrum

0/ 'J

1/ 2 3/ 2 5/ 20 0 0 1 0 0( ) ( ) ( ) ( ) , 2bkgf x x m a x m a x m m m m

BES III

Stat. sig. is conservatively estimated:fit range, background shape, contribution of extra resonances

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

2121

Resonance M( MeV/c2) ( MeV/c2) Stat.Sig.

X(1835) 1836.5±3.0+5.6-2.1 190.1±9.0+38

-36 >20σ

X(2120) 2122.4±6.7+4.7-2.7 83±16+31

-11 7.2σ

X(2370) 2376.3±8.7+3.2-4.3 83±17+44

-6 6.4σ

X(1835) consistent with 0+

BESIII fit results:

PWA is needed to understand these structures.

BESIII

X(1835) , X(2120), X(2370) at BESIII

0.49 -40.52

-( / (1835)) ( (1835) ')

(2.87 0.09( ) ( )) 10

BR J X BR X

stat syst

For the X(1835):

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• 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.

Summary of X(1835), X(2120) & X(2370) in J/(’+-)

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Observation X(1870) in J/X, Xa0(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

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X(1870) in J/X, Xa0(980)

M(a0(980)) M(+) non-a0(980)

M(+) M()

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.

• With a0(980): • Veto a0(980):

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f1(1285) (1405)

BR(J/X, X )

X(1870): 7.2

Fitting results of X(1870) Fitting with three resonances (acceptance weighted BW Gauss) Background component described by Polynomial function

M(a0(980))

① Contribution from non- and/or non-a0(980) BG events

② Contribution from J/b1(1235)a0(980)

③ Contribution from “PS” process of J/a0(980)

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Summary of X(1870) in J/(+-)

BESIIIarxiv :1107.1806

Accepted by PRL.

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Summary and Prospects

Huge data samples collected for charmonium decays at BESIII. A lot of results have been obtained,The spin-parity of the pp mass threshold enhancement in

J/γ pp 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.

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many thanks for your attention !