Observation of threshold Observation of threshold enhancement from enhancement from

Ji XiaobinJi Xiaobin

IHEPIHEP

Oct. 28 – Nov. 1, 2006Oct. 28 – Nov. 1, 2006

/J pp pp

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

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ContentContent

IntroductionIntroduction Events SelectionEvents Selection Results and DiscussionResults and Discussion SummarySummary

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L ~ L ~ ~5~5101030 30 /cm/cm22ss at J/ at J/ peak peak

EEcmcm~~2-5 GeV2-5 GeV

The Beijing Electron Positron ColliderThe Beijing Electron Positron Collider

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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=1.78%(1+p2) z = 3.1 cm

BESII DetectorBESII Detector

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World J/World J/ Samples (10 Samples (1066))

0

10

20

30

40

50

60

MarkI I I DM2 BES I BES I I

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Events SelectionEvents Selection

2 good charged tracks2 good charged tracks 11 (isolated from charged tracks) (isolated from charged tracks) Particle ID for both charged tracksParticle ID for both charged tracks 4C-fit4C-fit

The Analysis of The Analysis of /J pp

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mass from selected events mass from selected events

Besides Besides C C peak, peak,

there is a clear there is a clear enhancement enhancement near threshold.near threshold.

pp

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0/ (data)J pp

BackgroundsBackgrounds

Main backgrounds remained after selection Main backgrounds remained after selection for mass peak near thresholdfor mass peak near threshold

0

/ (phase space)

/

J pp

J pp

No clear enhancement No clear enhancement

near thresholdnear threshold

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Fit Signal with an S(P)-wave BWFit Signal with an S(P)-wave BW

200

220

2

312000

)()(

)/(

MMM

kqqMBW

l

q = daughter momentum q0 = daughter momentum @ peak

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Fit resultsFit results

M(pp)-2mp (GeV)

0 0.1 0.2 0.32/dof=56/56

BESII

fitted peak location

J/ψ γpp

M=1859 MeV/c2

< 30 MeV/c2 (90% CL)

+3 +510 25

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threshold

observed peak

BW “peak”

High Statistics is crucial to the determination of BW “peak” belowThreshold.

Mass DeterminationMass Determination

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No turnover at thresholdpeak mass must be <2mp

weight events by q0/q:(i.e. remove threshold phase space factor)

M(pp)-2mp (GeV)

BESII

Is MIs Mpeakpeak real less than 2m real less than 2mpp ? ?

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P-wave fit??

M=1876.4 ± 0.9 MeV = 4.6 ± 1.8 MeV

2/dof=59/56

OK!

M=2mp

BESII

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cos distribution

1+cos2(expected for J/

)

sin2

M(pp)<1.9 GeV BESII

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Further ChecksFurther Checks

Only selected events with POnly selected events with Ppp > 0.4 GeV/c > 0.4 GeV/c22

PID: dE/dx PID: dE/dx TOF + dE/dx TOF + dE/dx

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efficiencyefficiency

Other tests(p>0.4)Other tests(p>0.4)

M = 1859 M = 1859 2 MeV 2 MeV

= 0 = 0 19 MeV 19 MeV

recrec dEdxdEdx

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Other tests(PID)Other tests(PID)

P(GeV/c)P(GeV/c)

TOFTOF

P(GeV/c)P(GeV/c)

PHM

PHM

PP dE/dxdE/dx

TOF+dE/dxTOF+dE/dx

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Other tests(Other tests(PID PID dE/dxdE/dxTOF+dE/dxTOF+dE/dx))

M = 1856 M = 1856 2 MeV 2 MeV

= 0 = 0 22 MeV 22 MeV

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The results are compatible with The results are compatible with publish onespublish ones

Further ChecksFurther Checks

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Possible understandings of the Possible understandings of the new observation new observation

Exclude interpretations of known resonanceExclude interpretations of known resonancess — Could it be a tail of a known resonance?— Could it be a tail of a known resonance?

— — FSI (Final States Interaction)?FSI (Final States Interaction)? Baryonium interpretationBaryonium interpretation

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Could it be a tail of a known resonance?

0 resonances in PDG tables:(1760) M=1760 = 60 MeV

(1800) M=1801 = 210 MeVDefinitely excluded! ( >>5 )

2/dof=323/58 2/dof=412/58

BESIIBESII

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Pure FSI disfavoredPure FSI disfavored

I=0 S-wave FSI CANNOT fit the BES data.I=0 S-wave FSI CANNOT fit the BES data.

FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0)

58/192../2 fod

FSI * PS * eff + bck

ppp mM 2

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pp bound state (baryonium)?

+ n +

deuteron:

loosely bound 3-q 3-q color singlets with Md

= 2mp-

baryonium:

loosely bound 3-q 3-q color singlets with M

b = 2mp-?

attractive nuclear force attractive force?

There is lots & lots of literature about this possibility

E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949)

…I.S. Sharpiro, Phys. Rept. 35, 129 (1978)C.B. Dover, M. Goldhaber, PRD 15, 1997 (1977)…A. Datta, P.J. O’Donnell, PLB 567, 273 (2003)]M.L. Yan et al., hep-ph/0405087B. Loiseau et al., hep-ph/0411218…

Observations of this structure in other decay modes are desirable.

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学术评价学术评价 多夸克态的研究成为当前高能物理研究的新热点。 欧洲核子研究中心（ CERN ）著名的理论物理学家 J. Ellis 和美

国斯坦福直线加速器中心（ SLAC ）著名理论物理学家 S.J. Brodsky 分别在有关评述文章和国际会议报告中称最近这些新发现 “令人惊异” ，“增强了发展 QCD 理论的需要”。李政道教授也致信高能所表示祝贺，信中评价说：“这是一个十分重要的成果，也是物理学上很有意义的工作。” 德国著名强子谱学专家 E. Klepmt 教授将这一奇异增长结构称为 “ BES 共振态” 并将这一新发现列入教材。

到目前为止文章已经被引用 116 次。 促进了 BES 在相关领域的深入研究。

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SummarySummary

A narrow peak seen near 2mp in the Mpp distribution for decays using BES-II 58M J/ events

No narrow peak in decays Any PDG particles can be excluded, including possi

ble effect of interference. Its mass and unexpected narrow width suggest a p

ossible interpretation as “deutron like” proton-antiproton bound state (baryonium)(baryonium)

J/ψ γpp0J/ψ π pp

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Interference effect of several resonances?Interference effect of several resonances?

Three 0Three 0 resonances : resonances : (1760) : (1760) : M=1760 ; M=1760 ; = 60 MeV= 60 MeV (2150) : (2150) : M=2150 ; M=2150 ; = 200 MeV= 200 MeV

(2190) : (2190) : M=2190 ; M=2190 ; = 500 MeV= 500 MeV

Fitted CL: Fitted CL: 6 ×106 ×10 — — Excluded by more than Excluded by more than 4.5 4.5 — — The inconsistency is The inconsistency is mainly from the threshold mainly from the threshold peakpeak

BESII

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Interference effect of several resonances?

Three 0 resonances : X : to be determined by fit (2150) : M=2150 ; = 200 MeV

(2190) : M=2190 ; = 500 MeV

Fitted mass and width:

M = 1864 ± 3 MeV

= 0 ± 17 MeV

Basically remain the same as the results without any interference.

BESII

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FSI ExplanationFSI Explanation

A.Sibitsev, PRD71, 054010(2005)A.Sibitsev, PRD71, 054010(2005)

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Re-fit to J/Re-fit to J/pp pbar including FSI pbar including FSI

Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0)

M = 1830.6 6.7 MeV

= < 153 MeV @90%C.L.

ppp mM 2

In good agreement with X(1835)

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54264 obsN

MeVm 7.21.67.1833

MeV7.73.207.67

410)4.04.02.2()()( XBXJB

7.7The +- mass spectrum for decaying into +- and

59.18.0 10)4.00.7()()(:..

ppXBXJBfc

J

PRL 95, 262001 (2005)

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中国物理学家所做主要贡献 选出的 事例统计量比美方高选出的 事例统计量比美方高 66 －－ 77 倍倍（主要是由（主要是由

于美方的于美方的 anti-pi0anti-pi0 条件引起的）条件引起的） 发现选择效率的质量依赖关系。发现选择效率的质量依赖关系。 坚持使用坚持使用 SIMBESSIMBES ，而美方一开始坚持使用，而美方一开始坚持使用 SOBERSOBER 。（。（ SISI

MBESMBES 是中方许多人共同努力的结果）。是中方许多人共同努力的结果）。 发现美方的分析程序中发现美方的分析程序中 Prob(PID)>0.02Prob(PID)>0.02 的条件有偏，去掉该的条件有偏，去掉该

条件后，条件后，双方联合分析程序基本与中方程序一致双方联合分析程序基本与中方程序一致。。 首先开始首先开始 MC Input/OutputMC Input/Output 检查。检查。 改进产生子。改进产生子。 发现拟合程序中的问题。发现拟合程序中的问题。

J/ψ γpp

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With threshold kinematic contributions removedWith threshold kinematic contributions removed,, there are there are very smooth threshold enhancements in very smooth threshold enhancements in elastic “matrix eleelastic “matrix element”ment” and very small enhancement in and very small enhancement in annihilation “matrix elemeannihilation “matrix element”: nt”:

much weaker than what BES observed !much weaker than what BES observed !

NO strong dynamical threshold enhancement inNO strong dynamical threshold enhancement in cross sections (at LEAR) cross sections (at LEAR)

pmppM 2)(

|M|2 |M|2BES BES

elasticelasticM ~|| 2 annlabann PM ~|| 2

Both arbitrary normalization Both arbitrary normalization

pp

pp

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Observation of X(1835) in

The +- mass spectrum for decaying into +- and

Statistical Significance 7.7

J

J