轻强子谱的实验研究
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轻强子谱的实验研究. 沈肖雁 中国科学院高能物理研究所 [email protected] 2013 年 7 月 9 日 (中国科技大学). 目录. 引言 介子谱 常规介子谱 胶子球谱 ( glueball) 混杂态 (hybrid) 多夸克态( Multi-quark state ) 重子谱 实验结果. 量子色动力学 (QCD)-- 描述强相互作用的基本理论: 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。

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轻强子谱的实验研究

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3693165

轻强子谱的实验研究

沈肖雁

中国科学院高能物理研究所

[email protected]

2013年7月9日 (中国科技大学)


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目录

  • 引言

  • 介子谱

    • 常规介子谱

    • 胶子球谱 (glueball)

    • 混杂态 (hybrid)

    • 多夸克态(Multi-quark state)

  • 重子谱

  • 实验结果


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量子色动力学(QCD)-- 描述强相互作用的基本理论:

  • 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。

  • 然而,低能下(<3GeV) QCD 理论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,例如:

    自然界是否存在由新型强子构成的新的物质形态?


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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

格点QCD理论预言的胶子球谱

  • 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。

  • 对强子谱的研究则提供了大量强子结构的信息,推动了夸克模型的建立和量子色动力学的发展。

Y. Chen et al., PRD 73 (2006) 014516

4


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Heavy Quarkonia Spectra

(重夸克偶素谱)

cc

bb

Rich spectroscopy, various production schemes,

interesting decay scenarios


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夸克模型

在夸克模型中:

介子由(qq)构成

重子由(q q q)构成

one up quark (charge +2/3)

one down quark (charge -1/3)

one neutrino (no charge, “no” mass)

质子proton (uud)

composite

particles

nucleons

中子neutron(udd)


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新型强子态

  • 强子由 2个或 3个夸克组成:

    Naive Quark Model:

  • QCD 预言了新型强子的存在:

    • Multi-quark states:Number of quarks >= 4

    • (多夸克态)

    • Hybrids(混杂态): qqg,qqqg …

    • Glueballs(胶子球): gg, ggg …

Meson( qq )

Baryon(q q q)


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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.


Light hadron spectroscopy

Light hadron spectroscopy(轻强子谱)

  • Meson spectrum(qq) (介子谱)

  • New forms of hadrons(glueballs,hybrid states, multi-quark states)

  • Baryon spectrum (qqq) (重子谱)

Charmonium decays provide good lab.


Conventional meson spectrum

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.


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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.


Glueball spectrum

Glueball spectrum(胶子球谱)

  • 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.


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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) 014516


Glueball signatures

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).


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-- 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


Glueball signatures1

Glueball signatures

  • Flavor-blindness of glueball decays

    flavor singlet glueball decay width:


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Glueball signatures

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


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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:


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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.


Hybrid mesons

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


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Theoretical prediction on the decay modes of exotics


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  • 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


Multi quark states

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.


Where to find

Where to find?

  • Hunting for multi-quark states in πJ/ψ, πψ(2S), πcJ, …

    • Decays to charmonium thus has a cc pair!

    • With electric charge thus has two more light quarks!

       Nquark 4 !


Baryon spectrum

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- 1672.45 0.29 MeV


Two problems in qqq model

Two problems in qqq model


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Missing N* Resonances (uud, udd)

PDG2012

Theory predicts much more baryons than

what observed  missing baryons

(**)

not well-established


Order of masses for lowest states

Order of masses for lowest states

  • 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)


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  • The baryon spectrum reflects the underlying degrees of freedom and the effective forces between them.

  • Validate theoretical models

Baryon-meson

system


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QCD

N*, Δ*

LQCD

Models

N-N*

Reaction

Theory

Amplitude

analysis

Data


Charmonium decays ideal place for baryon spectroscopy study

Charmonium decays – ideal place for baryon spectroscopy study


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高能物理实验的三大主要工作方向

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


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北京谱仪探测器(BESIII)


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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

    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


Monte carlo mc

什么是 Monte Carlo?

Monte Carlo (MC)模拟

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.


Monte carlo

高能物理中的Monte-Carlo模拟

  • 产生子

    Theoretical model simulation

  • 探测器模拟


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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。

  • 通常,探测效率只能由 MC 模拟得出。

  • 因此,MC 模拟软件能否正确模拟实际数据,对能否获得正确的物理结果至关重要!


Resonance

什么是共振态(resonance)

  • 寿命极短的粒子被称作为共振态。

    已观测到的强子大多是共振态。(例:J/粒子)

  • 当粒子寿命 时,很难在探测器中留下径迹,即不能直接被探测到而只能通过其衰变产物的反应截面来观测。通常反应截面有类似共振现象的增强,因而被称为共振态。 (例:J/粒子的发现)

  • 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


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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


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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。


Light scalar mesons

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.


Why light scalar mesons are interesting

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.


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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


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The  pole in at BESII

M(+-)

Different parameterizations of BW are used in PWA.

Averaged pole:

BES, PLB 598 (2004) 149


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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


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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


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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


F 0 980 at bes

f0(980) at BES

BES II

Preliminary

  • Important parameters from PWA fit:

  • Large coupling with KK indicates big component in f0(980)

f0(980)

f0(980)


F 0 980 at kloe

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)


F 0 1370 at bes

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


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f0(1500):0++,M = 1507  5 MeV,  = 109  7 MeV

 2, 4, , ’, KK … (glueball favored modes)


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f0(1500) in J/  +- and 00 at BES

The channels fitted in PWA:

M(+- )

M(00 )


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Results

  • Lower 0++ : 0++ is strongly preferred over 2++

    f0(1500):

  • f0(1370) cannot be excluded.

  • Higher 0++: f0(1710) or f0(1790) or both?


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f0(1710): a long history of uncertainty.


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Appeared in gluon rich processes, not appeared in

gluon suppressed process.


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f0(1710) at BESII

PWA analysis shows

one scalar in 1.7 GeV region

Phys. Rev. D 68 (2003) 052003


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BES II

f0(1710)

  • Clear f0(1710) peak in J/  KK.

  • Nof0(1710) observed in J/   !

NO f0(1710)


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J/  +- and 00 at BES

M(+- )

0++ strongly favored.

M(00 )


About f 0 1500 and f 0 1710

About f0(1500) and f0(1710)

  • It is first clearly observed in J/ radiative decays.

  • Its production rate in J/ radiative decays:


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  • 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?


New f 0 1790 at bes

New f0(1790) at BES

BES II

  • A clear peak around 1790 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

f0(1790)

?

 f0(1790) is a new scalar !


Unusual properties of f 0 1370 f 0 1710 and f 0 1790

Unusual properties of f0(1370), f0(1710) and f0(1790)

  • f0(1710):

    • 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


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Observation of  thresholdenhancement in J/  

DOZI

OZI


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Clear  and  signals



M(K+K-)



M(K+K-)

M(+-0)

Dalitz plot

M2(g)

M(+-0)

M2(gw)


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A clear threshold enhancement is observed

Phase Space

Eff. curve

Side-bands

Side-bands do not have

mass threshold enhancement!


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  • 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) 162002


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J/   @ BESIII

Backgrounds estimated

from  and  sidebands

Backgrounds estimated

from inclusive MC -- mainly

from K*K


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PWA results at BESIII:

Is X(1810) the f0(1710)/f0(1790) or new state?


Study of system

Study of  system

PRL48 (1982) 458.

  • First observed f0(1710) from

  • J/ radiative decays to 

  • by Crystal Ball in 1982.

  • Crystal Barrel Collaboration (2002)

  • analyzed the three final states 000, 00and 0 with

  • K matrix formalism. Found a 2++ (1870), but no f0(1710).

  • E835 (2006): ppbar  0 , found f0(1500) and f0(1710).

  • WA102 and GAMS all identified f0(1710) in .


J @ besiii

J/ @ BESIII

  • Clear resonances

  • Very low BG level

M()


Preliminary pwa results of j

Preliminary PWA results of J/

  • f0(1710) and f0(2100)

  • are dominant scalars

  • f0(1500) exists (8.2 )

  • f2’(1525) is the

  • dominant tensor


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  • Situation of scalars above 1.0 GeV is still unclear. More experimental information is needed.

  • New states ?


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

Observation of an anomalous enhancement near the threshold of mass spectrum

J/ygpp

BES II

acceptance weighted BW

+3 +5

-10 -25

M=1859 MeV/c2

G < 30 MeV/c2 (90% CL)

X(1860)

c2/dof=56/56

0

0.1

0.2

0.3

3-body phase space

M(pp)-2mp (GeV)

acceptance


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Fit to J/ pp including FSI

M = 1830.6  6.7 MeV

 = 0  93 MeV

Include FSI curve from A.Sirbirtsev et al.(hep-ph/ 0411386) in the fit (I=0)

BES II Preliminary


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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 !


Not in b pp k at babar and belle

Not in B+ pp K+ atBaBarandBelle

Belle

BaBar

210 fb-1

BES II

X(1860)

  • 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.


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This narrow threshold enhancement is NOT observed in J/pp at BESII

J/ pp

No narrow strong enhancement

near threshold


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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.

    FSI interpretation of the narrow and strong pp threshold enhancement is disfavored.

PRD73, 032001(2006)

No enhancement

near threshold


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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.


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  • Confirmed by CLEOc and BESIII

  • fit with one resonance as BES did:

PRD 82, 092002 (2010)

CPC 34, 421 (2010)

M=1861 +6 -13+7-26 MeV/c2

G < 38 MeV/c2 (90% CL)


Pwa of j pp @ besiii

PWA of J/pp @ BESIII

PRL 108, 112003 (2012)

f0(2100) / f2(1910) fixed to PDG. Sig. of X(ppbar) >>30

Different FSI models  Model dependent uncertainty

83


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PWA of ’pp @ BESIII

Phys. Rev. Lett. 108, 112003 (2012)

Suppressed compared with 12% rule!


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Observation of X(1835) in

X(1835)

5.1 

X(1835)

6.0 


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Combine two channels

7.7

Statistical Significance 7.7 

X(1835)


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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.


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  • 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/0502127


X 1835 in j y gp p h at besiii

X(1835) in J/ygp+p-h’ at BESIII

  • PRL 108 (2011)112003

  • Fit with four resonances (acceptance weighted BW gaussian)

  • Three background components:

    • Contribution from non-’ events estimated by ’ sideband

    • Contribution from with re-weighting method

    • Contribution from “PS background”

Red line: estimated contribution of ①+ ②

Black line: total background

  • Stat. sig. is conservatively estimated:

    • fit range, background shape, contribution of extra resonances


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The angular distribution of the X(1835)

  • BESIII: PRL 108, 112003

  • 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.


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Why are X(2120) and X(2370) interesting?

  • 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/-->ππ' decay is a good channel for finding 0-+ glueballs.

  • Nature of X(2120)/X(2370)

    • pseudoscalar glueball ?

    • / excited states?

    • ……

PRD73,014516(2006) Y.Chen et al

PRD82,074026,2010

J.F. Liu, G.J. Ding and M.L.Yan

PRD83:114007,2011

J.S. Yu, Z.-F. Sun, X. Liu, Q.zhao

and more…

91


Observation of x 1870

Observation of X(1870)

BESIII: PRL 107, 182001 (2011)

BESIII 225M J/

The f1(1285), (1405)

and X(1870) primarily

decay via a0(980)±

X(1870)

(1405)/(1475)

f1(1285)

Is X(1870) a new

resonance, or

2(1870) or X(1835)?

Significance: 7.2 s

J/ywX,Xp+p-h

92


Besiii observation of the z c 3900 a charged charmonium like structure

BESIII: Observation of the Zc(3900) — a charged charmonium-like structure

BESIII: PRL110, 252001 (2013)

  • Select e+e- +-J/ @ 4.26 GeV

525/pb @4.26 GeV


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BESIII: PRL110, 252001 (2013)

BESIII

  • M = 3899.03.64.9 MeV

  •  = 461020 MeV

  • 307  48 events

Significance

>8


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BELLE:e+e- +-J/ from ISR

Belle: PRL 110, 252002(2013)

CLEOc data at 4.17 GeV

arXiv: 1304.3036

586/pb

  • M = 388551 MeV

  •  = 34124 MeV

  • 81  20 events

  • 6.1

  • M = 3894.56.64.5 MeV

  •  = 632426 MeV

  • 159  49 events

  • >5.2


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What is the nature of Zc(3900)?

  • Couples tocc

  • Has electric charge

  • At least 4-quarks

Many theoretical interpretations:

  • DD* molecule?

  • Tetraquark state?

  • Cusp?

  • Threshold effect?

More experimental information needed!

Other Zc partners exist?


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The observation of new N* peaks in

N*(1520)

N*(1535)

N*(1650)

N*(1675)

N*(1680)

N*(1440)?

?

Missing mass spectrum (GeV/c2)


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BESII: PRL 97 (2006) 062001

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)


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BESIII: PRL 110 (2013) 022001


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Summary


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