轻强子谱的实验研究. 沈肖雁 中国科学院高能物理研究所 shenxy@ihep.ac.cn 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（ Multiquark 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
沈肖雁
中国科学院高能物理研究所
shenxy@ihep.ac.cn
2013年7月9日 （中国科技大学）
量子色动力学(QCD) 描述强相互作用的基本理论：
自然界是否存在由新型强子构成的新的物质形态？
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
Y. Chen et al., PRD 73 (2006) 014516
4
Heavy Quarkonia Spectra
（重夸克偶素谱）
cc
bb
Rich spectroscopy, various production schemes,
interesting decay scenarios
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)
新型强子态
Naive Quark Model：
Meson（ qq ）
Baryon（q q q）
Multiquark 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.
Charmonium decays provide good lab.
In the quark model framework, the Hamiltonian
for a colorsinglet qq system can be written as:
With an explicit form of V(r), qq spectrum can be
produced.
Spindependant forces between quarks result in fine
and hyperfine structures in the hadron spectroscopy.
However, CQM is only a phenomenological model.
It's not derived from the underlying theory of the
strong interactionQuantum Chromodynamics (QCD).
Hence the CQM spectrum is not necessarily the
same as the physical spectrum in QCD.
Glueball spectrum from LQCD
Y. Chen et al., PRD 73 (2006) 014516
 Scalar nonet (JPC = 0++)
The scalar nonet should lie in the mass range
of 12 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).
 Pseudoscalars (JPC = 0+)
(1295): the radial excitation of ’(958)
(1475): ss state
(1405): 0+ glueball
flavor singlet glueball decay width:
Glueball signatures
Glueball signatures
Gluons are charge neutral, glueball production in collision and glueball decays into are suppressed.
Glueballs have large stickiness.
Stickiness:
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.
0+, 0, 1+, 2+, 3+,……, exotic states
…
Theoretical prediction on the decay modes of exotics
Nquark 4 !
Ex.theoretical calculation: m 1670 MeV (sss)
m 1672.45 0.29 MeV
Missing N* Resonances (uud, udd)
PDG2012
Theory predicts much more baryons than
what observed missing baryons
(**)
not wellestablished
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)
Baryonmeson
system
QCD
N*, Δ*
LQCD
Models
NN*
Reaction
Theory
Amplitude
analysis
Data
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
北京谱仪探测器（BESIII)
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
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
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.
Theoretical model simulation
探测结果 ＝ 理论模型 ×探测效率
已观测到的强子大多是共振态。（例：J/粒子）
其质量不确定范围，与寿命成反比： （h为普朗克常数）
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
例：A → B + C
(BreitWigner 函数)
质量宽度
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
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.
The study of
The pole in at BESII
M(+)
Different parameterizations of BW are used in PWA.
Averaged pole:
BES, PLB 598 (2004) 149
observation of in ’+J/
Phys. Lett. B 645 (2007) 19
The study of
of
constant amplitude or a broad 0+ resonance in K
BES observed in J/K*KKK
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
BES II
Preliminary
f0(980)
f0(980)
Background subtracted
KLOE
Preliminary
f0(980)
f0(980)
BES II
Preliminary
f0(1370)
NO f0(1370)
PWA 0++ components
f0(1500):0++,M = 1507 5 MeV, = 109 7 MeV
2, 4, , ’, KK … (glueball favored modes)
f0(1500) in J/ + and 00 at BES
The channels fitted in PWA:
M(+ )
M(00 )
Results
f0(1500):
f0(1710): a long history of uncertainty.
Appeared in gluon rich processes, not appeared in
gluon suppressed process.
f0(1710) at BESII
PWA analysis shows
one scalar in 1.7 GeV region
Phys. Rev. D 68 (2003) 052003
BES II
f0(1710)
NO f0(1710)
J/ + and 00 at BES
M(+ )
0++ strongly favored.
M(00 )
BES II
Inconsistent with what we observed in J/ , KK
f0(1790)
?
f0(1790) is a new scalar !
Scalar Puzzle
Observation of thresholdenhancement in J/
DOZI
OZI
Clear and signals
M(K+K)
M(K+K)
M(+0)
Dalitz plot
M2(g)
M(+0)
M2(gw)
A clear threshold enhancement is observed
Phase Space
Eff. curve
Sidebands
Sidebands do not have
mass threshold enhancement!
.
Further look in , K*K*, …. is desirable !
Phys. Rev. Lett., 96 (2006) 162002
J/ @ BESIII
Backgrounds estimated
from and sidebands
Backgrounds estimated
from inclusive MC  mainly
from K*K
PWA results at BESIII:
Is X(1810) the f0(1710)/f0(1790) or new state?
PRL48 (1982) 458.
M()
Phys. Rev. Lett. 91, 022001 (2003)
Observation of an anomalous enhancement near the threshold of mass spectrum
J/ygpp
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
3body phase space
M(pp)2mp (GeV)
acceptance
Fit to J/ pp including FSI
M = 1830.6 6.7 MeV
= 0 93 MeV
Include FSI curve from A.Sirbirtsev et al.(hepph/ 0411386) in the fit (I=0)
BES II Preliminary
X(1860) has large BR to pp
(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 !
Belle
BaBar
210 fb1
BES II
X(1860)
This narrow threshold enhancement is NOT observed in J/pp at BESII
J/ pp
No narrow strong enhancement
near threshold
This narrow threshold enhancement is NOT observed in (1S)pp at CLEO
FSI interpretation of the narrow and strong pp threshold enhancement is disfavored.
PRD73, 032001(2006)
No enhancement
near threshold
pp bound state (baryonium)?
There is lots & lots of literature about this possibility
deuteron:
baryonium:
attractive nuclear force
attractive force?
+
n
+

loosely bound 3q 3q color singlets with Md = 2mp e
loosely bound
3q 3q color singlets with Mb = 2mpd ?
Observations of this structure in other decay modes are desirable.
PRD 82, 092002 (2010)
CPC 34, 421 (2010)
M=1861 +6 13+726 MeV/c2
G < 38 MeV/c2 (90% CL)
PRL 108, 112003 (2012)
f0(2100) / f2(1910) fixed to PDG. Sig. of X(ppbar) >>30
Different FSI models Model dependent uncertainty
83
PWA of ’pp @ BESIII
Phys. Rev. Lett. 108, 112003 (2012)
Suppressed compared with 12% rule!
Observation of X(1835) in
X(1835)
5.1
X(1835)
6.0
Combine two channels
7.7
Statistical Significance 7.7
X(1835)
X(1835) could be the same structure as X(1860) indicated by pp mass threshold enhancement
G.J. Ding and M.L. Yan, hepph/0502127
Red line: estimated contribution of ①+ ②
Black line: total background
The angular distribution of the X(1835)
Why are X(2120) and X(2370) interesting?
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
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/ywX,Xp+ph
92
BESIII: PRL110, 252001 (2013)
525/pb @4.26 GeV
BESIII: PRL110, 252001 (2013)
BESIII
Significance
>8
BELLE：e+e +J/ from ISR
Belle: PRL 110, 252002(2013)
CLEOc data at 4.17 GeV
arXiv: 1304.3036
586/pb
What is the nature of Zc(3900)?
Many theoretical interpretations:
More experimental information needed!
Other Zc partners exist?
The observation of new N* peaks in
N*(1520)
N*(1535)
N*(1650)
N*(1675)
N*(1680)
N*(1440)?
?
Missing mass spectrum (GeV/c2)
BESII: PRL 97 (2006) 062001
N*(2065)
BW fit yields:
PWA is performed.
BESIII: PRL 110 (2013) 022001
Summary