轻强子谱的实验研究 沈肖雁 中国科学院高能物理研究所 2008年6月23日.

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1 轻强子谱的实验研究 沈肖雁 中国科学院高能物理研究所 2008年6月23日

2 主要内容 简介 介子谱 常规介子谱 胶子球谱 混杂态 多夸克态 重子谱

3 什么是高能物理 ? 高能物理，又称粒子物理, 它研究 粒子物理, 是分子物理, 原子物理, 原子核物理的自然发展与深化
物质的基本结构、基本性质 物质之间相互作用 粒子物理, 是分子物理, 原子物理, 原子核物理的自然发展与深化 粒子物理与天体物理和宇宙学密不可分 无穷小 无穷大

4 21世纪自然科学研究的三个最重要前沿 物 质 基 本 结 构 宇宙起源与演化 生命起源及其本质 物质科学是一切现代科学的基础
粒子物理与宇宙学： 联合与交叉 同步辐射与中子散射: 提供关键的研究手段 物质科学是一切现代科学的基础

5 高能物理研究的范围及其要解决的基本问题:
1。寻找构成物质世界的基本元素 2。研究物质间的相互作用规律及其统一模式 3。明了基本粒子的性质 4。理解宇宙起源与演化的规律 高能物理研究涉及国家安全和经济发展的关键技术 加速器 核探测技术与核电子学 真空，微波，高频，低温，网络，自控，。。。

6 粒子物理要解决的基本问题: 1.寻找构成物质世界的基本元素
粒子物理要解决的基本问题: 1.寻找构成物质世界的基本元素 物质无限可分？ 哲学命题与科学问题的区别 同样的问题, 近似的理论 哲学命题: 思辩 科学问题: 定量(数学), 实验 粒子物理标准模型: 一种能定量描述与解释所有实验现象的理论 类似于元素周期表：夸克模型

7 1947年前，我们只知道很少的“粒子”，如质子、中子、电子、μ子等，人们认为这些粒子就是构成物质的最小单元，称之为“基本粒子”。
此后，在宇宙线实验和粒子加速器实验中发现了大量的粒子： π，π0，K，K0 ，K0 ，Λ，，Ξ，Δ …约几百种。 有的寿命很短，产生出来很快就蜕变成别的粒子。 问题：是不是这几百种粒子都是 “基本”的？ 王淦昌发现反西格玛负超子

8 介子由（qq）构成 重子由（qqq）构成 + (ud ) 质子 (uud)
1963年, 根据大量的实验数据, 盖尔曼等猜测这些粒子具有内部结构,并给出了计算这些粒子质量的公式 盖尔曼的夸克模型：共有三种夸克 u,d,s 60年代中期,中国的粒子物理学家曾提出 了层子模型 介子由（qq）构成 重子由（qqq）构成 + (ud ) 质子 (uud) M. Gell-Mann 1969 Nobel

9 质量公式预言 m- 1670 MeV 实验 m- 1672.45 0.29 MeV
s s K0(ds) K+(us) K*0 K*+  +(ud) + 0 0 -(u d)  I3 - I3  K-(su) K0(sd) K*- K*0 自旋为0 自旋为1 uu-dd 0 = 2 △- s △0 △+ △++ (ddd) (uuu) (udd) (uud) n(udd) p(uud) *- 0 *+ (dds) (uds) (uus) 0 (uds) + (uus) -(dds) I3 0 *- *0 (dss) (uss) - (sss) -(dss) 0(uss) 质量公式预言 m- 1670 MeV 实验 m- 0.29 MeV

10 建立夸克模型的关键实验: 电子轰击质子(1972)
质子并不是一个几何点。它有大小，其半径 10-13cm，电荷就分布在这样一个小空间范围 质子内部分布着大量的点电荷 定量分析表明,质子是由三个夸克组成                          e Jerome I. Friedman 等，1992 Nobel

11 1974年—丁肇中、B. Richter 发现 J/ 粒子
→ charm夸克 (c) mc ~ 1.5GeV J/Ψ 由(cc )构成。 1977年—L.Lederman 发现  ( 9.5GeV ) → Beauty (Bottom) (b) mb ~ 5GeV (9.5)由(bb )构成 1994年—Fermilab，CDF组发现 Top 夸克(t) mt ~ 176GeV

12 “基本” 粒子 从轻到重 电荷 +2/3 t u c 夸克 ( q ) -1/3 b d s ne nm nt 轻子 ( l ) -1 e
nt 轻子 ( l ) -1 e m t

13 粒子物理要解决的基本问题: 2. 研究物质之间的相互作用
粒子物理要解决的基本问题: 研究物质之间的相互作用 物质之间已知的相互作用 引力相互作用 电磁相互作用 弱相互作用 强相互作用 相互作用的传播 所有的相互作用均通过传播子以光速传播 引力: 质量, 引力子(?) 电磁力: 电荷, 光子 宏观(经典)作用力 微观(量子)作用力

14 弱电统一 弱作用本质上与电磁作用是同一种力,就象电与磁是同一种力,均可由麦克斯韦方程描述一样
弱电统一理论70年代由温伯格等提出,其基础是杨振宁与Mills 提出的杨- Mills规范场理论 Rubbia 等80年代通过实验证实了弱电统一理论 问题： 弱作用: 弱荷, W, Z0 W, Z0 有质量，如何传播相互作用？ 解决办法： W, Z0 与一种叫做Higgs 的粒子相互作用 寻找Higgs 粒子是目前粒子物理研究的首要任务 Carlo Rubbia 1984 nobel

15 强相互作用: 量子色动力学 描述强相互作用的理论。 强子（参与强相互作用的粒子）由夸克组成。 夸克与胶子是有颜色的（色荷）。
“夸克渐进自由”为理论基础。 强相互作用的渐近自由理论已被实验所证实。

16 标准模型是粒子物理的基本理论

17 ｝ 粒子物理－标准模型理论 粒子物理是研究物质深层结构和相互作用的基础学科： 始终处于科学发展的最前沿 物质结构：物质由三代轻子与夸克构成:
自然界中四种相互作用中的三种:  BES -粲物理研究 ｝ 电磁作用 弱作用 电弱统一理论 (EW) 强作用 量子色动力学(QCD)

18 夸克模型 在夸克模型中： 介子由（q q）构成 重子由（q q q）构成

19 标准模型中的基本粒子分类 u c t e   d s b e   夸克 轻子
夸克和轻子 （matter constituents） 六种夸克和六种轻子分为三代：(三代费米子—自旋为半整数的粒子) 中间玻色子 （自旋为整数的粒子）－传播相互作用 Force Carrier：光子（γ ）、W粒子、Z粒子 电弱相互作用 胶子（gluon）强相互作用 Higgs 玻色子 －决定物质质量 标准模型中唯一尚未发现的粒子 u c t e   d s b e   夸克 轻子

20 基本粒子分类（名词）常识 按质量分类 (old convention) 轻子（lepton）：例－电子（e）、中微子 强子
介子（meson） ：例－π 介子 重子（baryon）：例－质子、中子 强子 后来，介子和重子因参加强相互作用被统称为强子。 自然界现已发现大约140种介子和大约120种重子，它们 是否还有深层结构？

21 标准模型（EW＋QCD）的检验 以在欧洲核子物理中心（CERN）的 LEP 对撞机上的四个实验为主，对标准模型，尤其是弱电理论进行了大量精确检验，证明了标准模型的巨大成功。 标准模型建立发展的三十多年中，多项获诺贝尔物理奖。

22 量子色动力学（QCD） 在高能（>10 GeV) 下预言的“渐近自由”现象已被大量实验所证实。“渐近自由” 的发现获得 2004 年 Nobel 奖。 低能下( <3GeV) 尚有待进一步实验检验，尤其 是有许多重大问题亟待实验回答： 低能下如何描述强相互作用系统？ 自然界是否存在新型强子和新的物质形态？

23 BES实验-粲物理研究依托于大科学装置
(BEPCII)/(BESIII) 环周长： 241 米 束流能量 GeV 202 米 物理目标 BES 1-2.1GeV的正负电子对撞可以产生大量的粲偶素（J/，(2S)， cJ 和 (3770)等）、粲介子和  轻子。

24 BESIII/BEPCII（今年7月即将运行取数） BEPCII：设计亮度提高100倍 BESIII: 高性能探测器

25 谱学研究是人类探索与认识微观世界自然规律的重要手段
通过对原子光谱的研究获得原子结构的知识，从而奠定了原子物理基础,推动量子力学的建立和发展。 通过对核谱的研究深入理解了原子核的内部结构 对强子谱的研究则提供了大量强子内部结构的信息，推动了夸克模型的建立和量子色动力学的发展。

26 Hadron spectroscopy The ultimate goal of studying the hadron spectroscopy is to learn the dynamics of the constituent interactions. The failure of perturbative expansion for QCD in the light hadron sector. There exist phenomenological approaches and lattice QCD (LQCD) calculations. The LQCD has experienced drastic improvements along with the fast development of computing resources. But there still exist a lot of technical difficulties in the simulation of a fully non-perturbative QCD process. Experimental data will provide necessary constraints on the parameters introduced to the theory.

27 New forms of hadrons Hadrons consist of 2 or 3 quarks：
Naive Quark Model： QCD predicts the new forms of hadrons: Multi-quark states ：Number of quarks >＝ 4 Hybrids ： qqg，qqqg … Glueballs ： gg， ggg … Meson（ q q ） Baryon（q q q）

28 Main contents in the study of the hadron spectroscopy
Meson spectrum（qq) New forms of hadrons（glueballs,hybrid states, multi-quark states） Baryon sectrum (qqq)

29 Conventional meson spectrum
In the quark model framework, the Hamiltonian for a color-singlet qq system can be written as: With an explicit form of V(r), qq spectrum can be produced. Spin-dependant forces between quarks result in fine and hyperfine structures in the hadron spectroscopy.

30 However, CQM is only a phenomenological model.
It's not derived from the underlying theory of the strong interaction---Quantum Chromodynamics (QCD). Hence the CQM spectrum is not necessarily the same as the physical spectrum in QCD.

31 J/ decays provide ideal Lab for searchs for new forms of hadrons.
Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established. The observation of the new forms of hadrons will be a direct test of QCD. This has been one of the important physics goals for many experiments. J/ decays provide ideal Lab for searchs for new forms of hadrons.

32 Glueball spectrum Glueballs are bound states of at least 2 or 3 gluons in a color - singlet due to the non-Abelian property of QCD Early phenomenologies find rather light masses for the scalar glueball in a potential model. Other QCD-based approaches produce larger masses for the scalar such as M=1.52 GeV in a flux-tube model and M=1.5 GeV in QCD sum rule calculations. In the last twenty years, extensive numerical studies have been carried out to calculate the glueball spectrum in LQCD. Although earliest LQCD predictions for the glueball masses vary significantly, nowadays, the predictions for several lightest glueballs converge to similar mass region despite of different approaches being used.

33 Glueball spectrum from LQCD
LQCD predicts the lowest glueball state is 0++. The mass is around 1.5 GeV – 1.7 GeV. LQCD predicts the next lightest glueball is 2++. The mass is around 2.4 GeV. The mix of glueball with ordinary qq meson makes the situation more difficult. The spectrum is from unquenched LQCD calculations Glueball candidates: f0(1500), f0(1700), fJ(2220), ... Y. Chen et al., PRD 73 (2006)

34 Glueball signatures no place in qq nonet
-- Scalar nonet (JPC = 0++) The scalar nonet should lie in the mass range of 1-2 GeV. a0(1450) and K0*(1430) in this mass region can be naturally assigned as the I=1 and I=1/2 multiplets. For I=0, there are more than two states f0(1370),f0(1500), f0(1710), f0(1790) and f0(1810). There also exists another scalar nonet below 1 GeV: f0(980), a0(980), (500), and (800).

35 -- Pseudoscalars (JPC = 0-+)
In Particle Data Book, five 0-+ states above 1 GeV are included in the particle lists: (1295), (1405), (1475), (1760), and (2225). The former three are well established by various experimental observations, while the latter two states need further confirmation. possible assignment: (1295): the radial excitation of ’(958) (1475): ss state (1405): 0-+ glueball

36 Glueball signatures Flavor-blindness of glueball decays
flavor singlet glueball decay width:

37 Glueball signatures Enhanced production in gluon rich processes such as pp central production, J/ radiative decays and pp annihilation.

38 Glueball signatures Reduced  couplings Gluons are charge neutral, glueball production in  collision and glueball decays into  are suppressed. Glueballs have large stickiness. Decay branching fractions incompatible with SU(3) predictions for states Stickiness:

39 The above criteria cannot individually provide
indisputable evidence for a glueball candidate with conventional quantum numbers, especially for the scalar glueball. However, putting all together the above expectations and criteria for a glueball candidate, one might still be able to place a bound on the glueball and qq contents of a state, and gain some insights into the complex issue of strong QCD.

40 Hybrid mesons Hybrid mesons are composed of a pair of qq and one explicit gluon g -- qqg From theoretical estimation, the production cross section of hybrid mesons is expected to be roughly the same as that of ordinary mesons. Hybrid mesons and ordinary mesons mix freely if they carry the same quantum numbers. The identification of hybrid mesons is very difficult unless they have exotic quantum numbers. 0+-, 0--, 1-+, 2+-, 3-+,……, exotic states …

41 Theoretical prediction on the decay modes of exotics

42 The lowest-lying exotic hybrid meson is predicted to be with the quantum number JPC=1-+ and a mass around 1.9 GeV/c2 Flux-tube model and LQCD give consistent prediction on the mass of 1-+. Comparison of decay width predictions

43 Multi-quark states Multi-quark states: number of quarks  4
The multi-quark states are expected to have very broad width since they can easily fall apart into mesons and/or baryons if their masses are above the sum of the masses of the hadrons in the final states. The multi-quark states may be only experimentally observable near the mass thresholds: either below or just above the mass thresholds, otherwise, the widths of multi-quark states might be too wide to be observed experimentally.

44 Baryon spectrum Baryons: qqq
Up to now all established baryons are ascribed to 3-quark (qqq) configurations The non-relativistic constituent quark model (NRCQM) provides an explicit classification for light baryons in terms of group symmetry. The classical simple 3q constituent quark model has been very successful in explaining the static properties, such as mass and magnetic moment, of the spatial ground states of the flavor SU(3) octet and decuplet baryons. Ex. theoretical calculation: m- 1670 MeV (sss) m- 0.29 MeV

45  the failure of NRCQM 3q model
Many deviations observed in experiment show much more complicated aspects of the strong QCD dynamics.  the failure of NRCQM 3q model 1. the lowest spatial excited baryon is expected to be a N*(uud) state with one quark in orbital angular momentum L=1, and hence should have negative P PDG: N*(1535) (1/2-) (?) N*(1440) (1/2+) (uud) (should be heavier than N*(1535)) *(1405) (1/2-) (uds) (should be 130MeV heavier than N*(1535) ) (N*(1535) partner) 2. It predicts a substantial number of ‘missing N* states' around 2 GeV/c2, which have not been observed so far.

46 Understanding of those deviations and looking for new states and phenomena beyond the NRCQM is the focus of the study of baryon spectroscopy. Our present knowledge on baryon spectroscopy is still poor. Many fundamental issues in baryon spectroscopy are still not well understood. an unsolved fundamental problem is: what are proper effective degrees of freedom for describing the internal structure of baryons?

47 Heavy Quarkonium Spectra
Rich spectroscopy, various production schemes, interesting decay scenarios

48 Bound states of qq, the QCD equivalents of positronium (e+e-) in QED
Simplest strongly interacting systems This opens avenues for effective theories of strong interactions: purely phenomenological potential models more recently NRQCD and much improved Lattice QCD Properties of these bound states, and their decays and productions are good labs. for QCD in both perturbative and non-perturbative regimes.

49 Probe QCD from various directions:
* QQ (QQ’) production, spectra and decays * qq and qqq spectra * non-qq and non qqq states

50 J/ decays provide ideal Lab for hadron spectroscopy
The lowest order diagrams for J/  hadrons:   c c c c * c J/ J/ J/ J/ c c c c 3-gluon Electromagnetic Radiative Via c a good lab to hunt for new forms of hadrons a good lab to study meson spectroscopy a good lab for excited baryon states

51 高能物理实验的三大主要工作方向 物理分析 理论研究 高能物理研究团队性强，也需要各方面人才 探测器设计、建造、取数 （硬件） 数据重建、模拟
（软件） 物理分析 理论研究 高能物理研究团队性强，也需要各方面人才

52 BESIII/BEPCII

53 北京谱议探测器 大型通用探测器，综合提供以下信息： 粒子鉴别；带电径迹的动量、位置；沉积能量 能够探测和鉴别的粒子
这些信息被用于物理分析的事例选择中 能够探测和鉴别的粒子 带电径迹：e， ， π，K，p （质子最容易被鉴别） 中性径迹：γ 最终在物理分析中重建出原始产生事例

54 Monte Carlo is a name of casino in Monaco.
Monte Carlo （MC）模拟 什么是 Monte Carlo? Monte Carlo is a name of casino in Monaco. gambling probability Monte Carlo is a technique of simulation based on probability using known theory/model/knowledge.

55 高能物理中的Monte-Carlo模拟 产生子 Theoretical model simulation 探测器模拟

56 高能物理实验中，MC 模拟软件至关重要 探测结果 ＝ 理论模型 × 探测效率 为了得到与理论模型可比较的物理结果，必须进行探测 效率修正。

57 什么是共振态（resonance） 已观测到的强子大多是共振态。（例：J/ 粒子） 寿命极短的粒子被称作为共振态。
共振态的（衰变）宽度Γ ： 其质量不确定范围，与寿命成反比： （h为普朗克常数） 共振态的宽度是理解其结构组成的重要基本性质(参数）。 相互作用越强 → 寿命越短 → 宽度越大 典型的强作用衰变宽度：≥100～200 MeV

58 共振态的观测与描述 衰变末态不变质量谱是观测共振态（反应截面）的重要手段。 例：A → B + C 共振态的数学描述
(Breit-Wigner 函数) 质量 宽度

59 事例选择 物理分析时，利用探测器提供的各种信息，通过事例选择去除本底，保留纯度较高的信号。
合理的事例选择应当尽量压低本底的同时，又尽量提高信号的选择效率。 好的事例选择条件是得到高质量物理结果的最关键的基础！ 尤其对新发现：因为新发现的信号通常较小 因而通常也是不同实验分析竞争最激烈之处。

60

61 Some results from BES 0++ states (scalars) New states Excited baryons
J/ World J/ Samples (×106) BESII 58M J/

62 Light Scalar Mesons Below 1 GeV: σ, κ, f0(980)
Above 1 GeV: f0(1370), f0(1500), f0(1710), f0(1790), f0(1810) Above 1 GeV, only 2 scalars in Quark Model.

63 Why light scalar mesons are interesting?
There have been hot debates on the existence of σ and κ . σ, κ and f0(980) are also possible mutiquark states. They are all near threshold. Lattice QCD predicts the 0++ scalar glueball mass ~ 1.6 GeV. f0(1500) and f0(1710) are good candidates.

64 The study of  evidence for a low mass pole in the early DM2 and BESI data on J/   . huge event concentration in the I=0 S-wave  channel seen in M ~ 500 – 600 MeV in the pp central production exp. to explain  scattering phase shift data， should be introduced in chiral perturbative theory. FNAL E761 exp. D+ +-+ data

65 The  pole in at BESII   M(+-)
Different parameterizations of BW are used in PWA. Averaged pole: BES, PLB 598 (2004) 149

66 observation of  in ’+-J/
Measure the universal pole position (552 - i232 MeV) World largest  signal (with ~ 40,000 tagged events) Phys. Lett. B 645 (2007) 19

67 The study of  A possible  pole is controversial.
Some analyses of LASS K scattering data needs (800), some don’t. Scadron et al. favors a nonet made up of , (800), f0(980) and a0(980). Julich group used t-channel exchanges to explain K scattering data. evidence of  in FNAL E791 data on D+ K-++ slightly lower statistics of CLEO D0 K-+0 data find no evidence of  FOCUS data on K+K-++ require K*0 interfere with either a constant amplitude or a broad 0+ resonance in K

68 BES observed  in J/K*KKK
A possible  pole is controversial. PWA result:  is needed in the fit. Pole position of : BES II 58 M J/ Phys. Lett. B 633 (2006) 681

69 f0(980) at BES BES II Important parameters from PWA fit:
Preliminary Important parameters from PWA fit: Large coupling with KK indicates big component in f0(980) f0(980) f0(980)

70 f0(980) at KLOE f0(980) is observed in    f0(980)    at KLOE (Background: ISR, FSR and ). The results support that f0(980) has large coupling with KK. Background subtracted KLOE Preliminary f0(980) f0(980)

71 f0(1370) at BES BES II Preliminary There has been some debate whether f0(1370) exist or not. f0(1370) clearly seen in J/  , but not seen in J/  . f0(1370) NO f0(1370) PWA 0++ components

72 f0(1500): 0++, M = 1507  5 MeV,  = 109  7 MeV  2, 4, , ’, KK … (glueball favored modes)

73 f0(1500) in J/  +- and 00 at BES
The channels fitted in PWA: M(+- ) M(00 )

74 Results f0(1500): Lower 0++ : 0++ is strongly preferred over 2++
f0(1370) cannot be excluded. Higher 0++: f0(1710) or f0(1790) or both?

75 f0(1710): a long history of uncertainty.

76 Appeared in gluon rich processes, not appeared in
gluon suppressed process.

77 f0(1710) at BESII PWA analysis shows one scalar in 1.7 GeV region
Phys. Rev. D 68 (2003)

78 Clear f0(1710) peak in J/  KK.
BES II Clear f0(1710) peak in J/  KK. No f0(1710) observed in J/   ! f0(1710) NO f0(1710)

79 J/  +- and 00 at BES
M(+- ) 0++ strongly favored. M(00 )

80 About f0(1500) and f0(1710) It is first clearly observed in J/ radiative decays. Its production rate in J/ radiative decays:

81 The production rate of f0(1500) in J/ radiative decays is lower than that of f0(1710):
It may indicate: f0(1710) has stronger coupling to gluons than f0(1500)  which one contains more glueball content?

82 New f0(1790) at BES BES II  f0(1790) is a new scalar !
A clear peak around MeV is observed in J/  . No evident peak in J/  KK. If f0(1790) were the same as f0(1710), we would have: Inconsistent with what we observed in J/   , KK BES II f0(1790) ?  f0(1790) is a new scalar !

83 Unusual properties of f0(1370), f0(1710) and f0(1790)
It dominantly decays to KK (not to )  It is mainly produced together with  (not )  What is it ? f0(1370) and f0(1790) They dominantly decays to  (not to KK)  It is mainly produced together with  (not )  What are they ?  Scalar Puzzle

84 Observation of  threshold enhancement in J/  
DOZI OZI

85 Clear  and  signals Dalitz plot M2(g) M2(gw)      M(K+K-)

86 A clear threshold enhancement is observed
Phase Space Eff. curve Side-bands Side-bands do not have mass threshold enhancement!

87 Further look in , K*K*,  …. is desirable !
PWA shows: the enhancement favors 0++ over 0-+ and 2++ . Is it the same 0++ observed in KK or  (f0(1710), or f0(1790)), or is it a glueball, or a hybrid …..? Further look in , K*K*,  …. is desirable ! Phys. Rev. Lett., 96 (2006)

88 Situation of scalars above 1. 0 GeV is still unclear
Situation of scalars above 1.0 GeV is still unclear. More experimental information is needed. New states ?

89 Observation of an anomalous enhancement near the threshold of mass spectrum
BES II J/ygpp acceptance weighted BW X(1860) M= MeV/c2 G < 30 MeV/c2 (90% CL) c2/dof=56/56 0.1 0.2 0.3 3-body phase space M(pp)-2mp (GeV) acceptance Phys. Rev. Lett. 91, (2003)   

90 Fit to J/  pp including FSI
M =  6.7 MeV  = 0  93 MeV Include FSI curve from A.Sirbirtsev et al.(hep-ph/ ) in the fit (I=0) BES II Preliminary

91 X(1860) has large BR to pp BES measured: For a 0-+ meson:
So we would have: (This BR to pp might be the largest among all PDG particles) Considering that decaying into pp is only from the tail of X(1860) and the phase space is very small, such a BR indicates X(1860) has large coupling to pp !

92 Not in B+  pp K+ at BaBar and Belle
210 fb-1 Belle X(1860) BES II The pp threshold enhancement observed in J/ decay is different from the enhancements observed by Belle and BaBar in B decay. The one in B decay can be explained by fragmentation.

93 This narrow threshold enhancement is NOT observed in J/ pp at BESII
No narrow strong enhancement near threshold

94 This narrow threshold enhancement is NOT observed in (1S)pp at CLEO
This result cannot be explained by pure FSI effect, since FSI is a universal effect. Pure FSI interpretation of the narrow and strong pp threshold enhancement is disfavored. PRD73, (2006) No enhancement near threshold

95 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/ B. Loiseau et al., hep-ph/ 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.

96 Observation of X(1835) in X(1835) 5.1  X(1835) 6.0 

97 Combine two channels 7.7 Statistical Significance 7.7  X(1835)

98 X(1835) could be the same structure as X(1860) indicated by pp mass threshold enhancement
X(1835) mass is consistent with the mass of the S-wave resonance X(1860) indicated by the pp mass threshold enhancement. On the other hand, if the FSI effect is included in the fit of the pp mass spectrum, the width of the resonance near pp mass threshold will become larger. The widths are consistent too.

99 X(1835) could be the same structure as pp mass threshold enhancement.
It is likely to be a pp bound state since it dominantly decays to pp when its mass is above pp mass threshold. ’ mode is expected to be the most favorable decay mode for a pp bound state below pp mass threshold G.J. Ding and M.L. Yan, hep-ph/

100 Observation of an enhancement near mass threshold in process
7 M = (2075 12  5) MeV Γ = (90  35  9) MeV BR = (5.9  1.4  2.0) 10-5 Phys. Rev. Lett. 93 (2004) preliminary (PS, eff. corrected) JP=1/2- is favored

101 Observation of a broad 1-- resonance in J/  K+K- 0
Phys. Rev. Lett. 97 (2006)

102 J/ K+K-0 0 background ? 0 sideband
X(1580) PID and kinematic fit can significantly reduce the dominant background from J/  + - 0.

103 What is this broad structure?
JPC should be 1--, 3--, …(Parity conservation) PWA results Following components are needed K*(892), K*(1410), (1700), X 1– is much better than 3— Pole position of X is Big destructive interference among X, (1700) and PS 1-- component Broad width  multiquark state?

104 The observation of new N* peaks in
? Missing mass spectrum (GeV/c2)

105 well-established N*’s below 2.0 GeV are fixed to PDG values.
Phys. Rev. Lett. 97 (2006) N*(2065) BW fit yields: PWA is performed. well-established N*’s below 2.0 GeV are fixed to PDG values. for N*(2065), L=1 is much worse than L=0 in the fit.  1/2+ or 3/2+ (improve log likelihood by 400) 1/2+ + 3/2+ (improve log likelihood further by 60)

106 Summary J/ decays -- excellent lab to study hadron spectroscopy and search for new hadronic states. Many results have been obtained so far by BES, but are still statistically or systematically limited. BEPCII/BESIII will take data in July of 2008. lum.: 100 times, detector: much better performance