Observation of threshold enhancement from Phys. Rev. Lett. 91, 022001(2003) Ji Xiaobin IHEP Oct. 28 – Nov. 1, 2006

Content Introduction Events Selection Results and Discussion Summary 晨光杯（桂林）

The Beijing Electron Positron Collider L ~ ~51030 /cm2s at J/ peak Ecm~2-5 GeV 晨光杯（桂林）

BESII Detector 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 晨光杯（桂林）

World J/ Samples (106) Largest from BES 晨光杯（桂林）

The Analysis of Events Selection 2 good charged tracks  1 (isolated from charged tracks) Particle ID for both charged tracks 4C-fit 晨光杯（桂林）

mass from selected events Besides C peak, there is a clear enhancement near threshold. 晨光杯（桂林）

Backgrounds Main backgrounds remained after selection for mass peak near threshold No clear enhancement near threshold 晨光杯（桂林）

Fit Signal with an S(P)-wave BW q = daughter momentum q0 = daughter momentum @ peak 晨光杯（桂林）

Fit results M(pp)-2mp (GeV) 0.1 0.2 0.3 +3 +5 fitted peak location 0.1 0.2 0.3 c2/dof=56/56 fitted peak location M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) +3 +5 -10 -25 晨光杯（桂林）

Mass Determination BW “peak” observed peak threshold observed peak BW “peak” High Statistics is crucial to the determination of BW “peak” below Threshold. 晨光杯（桂林）

Is Mpeak real less than 2mp ? weight events by q0/q: (i.e. remove threshold phase space factor) No turnover at threshold peak mass must be <2mp M(pp)-2mp (GeV) 晨光杯（桂林）

OK! P-wave fit?? M=1876.4 ± 0.9 MeV G = 4.6 ± 1.8 MeV M=2mp c2/dof=59/56 晨光杯（桂林）

cosqg distribution 1+cos2qg (expected for J/yg0-+ ) sin2qg M(pp)<1.9 GeV sin2qg 晨光杯（桂林）

Further Checks Only selected events with Pp > 0.4 GeV/c2 PID: dE/dx  TOF + dE/dx 晨光杯（桂林）

Other tests(p>0.4) rec  dEdx M = 1859  2 MeV efficiency 晨光杯（桂林）

Other tests(PID) P(GeV/c)  TOF P(GeV/c) PHMP dE/dx TOF+dE/dx 晨光杯（桂林）

Other tests(PID dE/dxTOF+dE/dx) M = 1856  2 MeV  = 0  22 MeV 晨光杯（桂林）

The results are compatible with publish ones Further Checks The results are compatible with publish ones 晨光杯（桂林）

Possible understandings of the new observation Exclude interpretations of known resonances — Could it be a tail of a known resonance? — FSI (Final States Interaction)? Baryonium interpretation 晨光杯（桂林）

Could it be a tail of a known resonance? 0-+ resonances in PDG tables: h(1760) M=1760 G = 60 MeV p(1800) M=1801 G = 210 MeV Definitely excluded! ( >>5  ) 2/dof=323/58 c2/dof=412/58 晨光杯（桂林）

Pure FSI disfavored I=0 S-wave FSI CANNOT fit the BES data. FSI * PS * eff + bck FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0) 晨光杯（桂林）

pp bound state (baryonium)? 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) Datta, P.J. O’Donnell, PLB 567, 273 (2003)] M.L. Yan et al., hep-ph/0405087 B. Loiseau et al., hep-ph/0411218 deuteron: baryonium: attractive nuclear force attractive force? + n + - loosely bound 3-q 3-q color singlets with Md = 2mp- e loosely bound 3-q 3-q color singlets with Mb = 2mp-d ? Observations of this structure in other decay modes are desirable. 晨光杯（桂林）

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。 晨光杯（桂林）

Summary A narrow peak seen near 2mp in the Mpp distribution for decays using BES-II 58M J/ y events No narrow peak in decays Any PDG particles can be excluded, including possible effect of interference. Its mass and unexpected narrow width suggest a possible interpretation as “deutron like” proton-antiproton bound state (baryonium) 晨光杯（桂林）

Thank You! 晨光杯（桂林）

Thank You! 晨光杯（桂林）

Interference effect of several resonances? Three 0-+ resonances : h(1760) : M=1760 ; G = 60 MeV h(2150) : M=2150 ; G = 200 MeV h(2190) : M=2190 ; G = 500 MeV Fitted CL: 6 ×10-6 — Excluded by more than 4.5  — The inconsistency is mainly from the threshold peak 晨光杯（桂林）

Interference effect of several resonances? Three 0-+ resonances : X : to be determined by fit h(2150) : M=2150 ; G = 200 MeV h(2190) : M=2190 ; G = 500 MeV Fitted mass and width: M = 1864 ± 3 MeV G = 0 ± 17 MeV Basically remain the same as the results without any interference. 晨光杯（桂林）

FSI Explanation A.Sibitsev, PRD71, 054010(2005) 晨光杯（桂林）

Re-fit to J/p 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. In good agreement with X(1835) 晨光杯（桂林）

7.7 The +- mass spectrum for  decaying into +- and   PRL 95, 262001 (2005) 晨光杯（桂林）

中国物理学家所做主要贡献 选出的 事例统计量比美方高6－7倍（主要是由于美方的anti-pi0条件引起的） 发现选择效率的质量依赖关系。 坚持使用SIMBES，而美方一开始坚持使用SOBER。（SIMBES是中方许多人共同努力的结果）。 发现美方的分析程序中Prob(PID)>0.02的条件有偏，去掉该条件后，双方联合分析程序基本与中方程序一致。 首先开始MC Input/Output检查。 改进产生子。 发现拟合程序中的问题。 晨光杯（桂林）

NO strong dynamical threshold enhancement in cross sections (at LEAR) With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:  much weaker than what BES observed ! |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization 晨光杯（桂林）

Observation of X(1835) in Statistical Significance 7.7  The +- mass spectrum for  decaying into +- and   晨光杯（桂林）