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Flux
tube
forms
What do we know about
between
qq
QCD Exotics?
Curtis A. Meyer, Carnegie Mellon University
What are QCD exotics?
Overview of evidence for
exotic quantum number states.
What does it all mean?
May 22, 2003
Curtis A. Meyer
1
Flux
tube
Normal Mesons
forms
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Non-quark-antiquark
0-- 0+- 1-+ 2+- 3-+ …
quark-antiquark pairs
orbital
u
s
d
J=L+S
P=(-1) L+1
C=(-1) L+S
G=C (-1) I
May 22, 2003
d
s
u
(2S+1)
1S
LJ
-+
0 = 0
3S = 1-1
r3,w3,f3,K3
r2,w2,f2,K2
L=2 r ,w ,f ,K
1 1 1 1
p2,h2,h’2,K2
3-2-1-2-+
a2,f2,f’2,K2
a1,f1,f’1,K1
L=1 a ,f ,f’ ,K
0 0 0 0
b1,h1,h’1,K1
2++
r,w,f,K*
L=0 p,h,h’,K
1-0-+
Curtis A. Meyer
radial
1++
0++
1+-
2
qq
Spectrum
qq Mesons
2.5
Glueballs
2.0
1.5
between
qq
Each box corresponds
to 4 nonets (2 for L=0)
Radial
excitations
2 +–
2 –+
1 ––
1– +
1 +–
1 ++
0 +–
0 –+
Hybrids
2 –+
0 –+
2 ++
Flux
tube
forms
0 ++
exotic
nonets
Lattice
1-+ 1.9 GeV
1.0
0++ 1.6 GeV
L=0
May 22, 2003
1
2
3
4
(L = qq angular momentum)
Curtis A. Meyer
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Flux
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Lattice QCD
Flux Tubes Realized
Flux
tube
From G. Bali
forms
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qq
Color Field: Because of self
interaction, confining flux tubes
form between static color charges
Confinement arises from
flux tubes and their
excitation leads to a new
spectrum of mesons
May 22, 2003
Curtis A. Meyer
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between
qq
Flux
tube
forms
Hybrid Mesons
between
qq
built on quark-model mesons
excited flux-tube
m=1
ground-state
flux-tube
m=0
normal mesons
CP={(-1)L+S}{(-1)L+1}
={(-1)S+1}
Flux-tube Model
m=0 CP=(-1) S+1
m=1 CP=(-1) S
May 22, 2003
1-+ or 1+-
r , w, f
S=0,L=0,m=1
S=1,L=0,m=1
J=1 CP=+
J=1 CP=JPC=0-+,0+-
JPC=1++,1--
1-+,1+-
(not exotic)
exotic
Curtis A. Meyer
2-+,2+5
Flux
tube
QCD Potential
forms
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qq
ground-state
excited flux-tube
flux-tube
m=1
m=0
linear potential
Gluonic Excitations provide an
experimental measurement of
the excited QCD potential.
Observations of exotic quantum number nonets are the
best experimental signal of gluonic excitations.
May 22, 2003
Curtis A. Meyer
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Flux
tube
forms
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Hybrid Predictions
qq
Flux-tube model: 8 degenerate nonets
1++,1-- 0-+,0+-,1-+,1+-,2-+,2+- ~1.9 GeV/c2
S=0
S=1
Lattice calculations --- 1-+ nonet is the lightest
UKQCD (97) 1.87 0.20
~2.0 GeV/c2
MILC (97)
1.97 0.30
-+
1
MILC (99)
2.11 0.10
Splitting  0.20  0.50
+0
Lacock(99)
1.90 0.20
+2
Mei(02)
2.01 0.10
In the charmonium sector:
1-+
4.39 0.08
Splitting = 0.20
+0
4.61 0.11
May 22, 2003
Curtis A. Meyer
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Decays of Hybrids
The angular momentum in the flux
tube stays in one of the daughter
mesons (L=1) and (L=0) meson.
between
qq
Lflux
Exotic Quantum Number Hybrids
p1 pb1 , pf1 , pr , ha1
h1p(1300)p , a1p
1:.25:.25:.20
1:1
b2  a1p , h1p , wp , a2p
h2  b1p , rp , wh
1:1:0.5:0.25
1:1:0.1
b0  p(1300)p , h1p
h 0  b 1p , h 1h
1:0.20
1:0.02
May 22, 2003
Curtis A. Meyer
Mass and model
dependent
predictions
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Exotic Quantum Numbers
1-+ in hp
Flux
E852 Results
tube
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qq
Mass = 1370 +-16+50-30 MeV/c2
p1(1400) Width= 385 +- 40+65
2
-105 MeV/c
The a2(1320) is the dominant
signal. There is a small (few %)
exotic wave.
p-p -> hp- p (18 GeV)
p1
a2
Interference effects show
a resonant structure in 1-+ .
(Assumption of flat background
phase as shown as 3.)
May 22, 2003
Curtis A. Meyer
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Exotic Quantum Numbers
1-+ in hp
Flux
tube
Crystal Barrel
forms
between
qq
Same strength as the a2.
p1(1400)
Mass = 1400 +- 20 +- 20 MeV/c2
Width= 310+-50+50-30 MeV/c2
Produced from states with one unit
of angular momentum.
Without p1 c2/ndf = 3, with = 1.29
hp0p-
May 22, 2003
Curtis A. Meyer
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qq
Significance of signal.
May 22, 2003
Curtis A. Meyer
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E852 Results
Exotic Quantum Numbers
1-+ in rp
-
+ - -
p pp p p p
+
-
p p p
+
-
-
M(p p p )
At 18 GeV/c
+
-
p p
GeV / c 
2
-
M(p p ) GeV / c
+
to partial wave analysis
-
2

suggests
p - p  r0 p - p
 p+ p - p - p
May 22, 2003
Curtis A. Meyer
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Flux
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forms
between
qq
Exotic Quantum Numbers
1-+ in rp
Flux
tube
E852 Results
forms
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qq
Correlation of
Phase
&
Intensity
1-+
Exotic
Signal
p1(1600)
Leakage
From
Non-exotic Wave
due to imperfectly
understood acceptance
May 22, 2003
+
-
-
M(p p p )
GeV / c 
2
3p m=1593+-8+28-47 G=168+-20+150-12
Curtis A. Meyer
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Exotic Quantum Numbers
1-+ in h’p
The p1(1600) is the
Dominant signal in h’p.
Mass = 1.5970.010 GeV
Width = 0.3400.040 GeV
p1(1600)  h’p
May 22, 2003
Curtis A. Meyer
Flux
tube
E852 Results
forms
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qq
p-p  h’p-p at 18 GeV/c
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Exotic Quantum Numbers
1-+ in f1p and b1p
p-p  hp+p-p-p
p-p  wp0p-p
E852 Results
Flux
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qq
p1(1600)  b1p
p1(1600)  f1p
Mass=1.7090.024 GeV
Width=0.4030.08 GeV
In both b1p and f1p, observe
Excess intensity at about
2GeV/c2.
Mass ~ 2.00 GeV,
Mass = 1.6870.011 GeV
Width ~ 0.2 to 0.3 GeV
Width = 0.2060.03 GeV
May 22, 2003
Curtis A. Meyer
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Exotic Quantum Numbers
1-+ in rp, b1p and h’p
Flux
VES Results
m=1.60.02 GeV/c2
G=0.290.03 GeV/c2
p1(1600) observed in pA reactions
b1p : h’p : rp = 1 : 1.00.3 : 1.6 0.4
p-Awpp
(A) (at 37 GeV/c)
b1p (1-+)
Phase wrt 2+
May 22, 2003
Curtis A. Meyer
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qq
Exotic Signals
Flux
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qq
p1(1400) Width ~ 0.3 GeV, Decays: only hp
weak signal in pp production (scattering??)
strong signal in antiproton-deuterium.
p1(1600) Width ~ 0.16 to 0.3 GeV, Decays rp,h’p,(b1p,f1p)
Only seen in pp production, (E852 + VES)
In a nonet, there should only be one p1 state.
p1 IG(JPC)=1-(1-+)
K1 IG(JPC)=
h1 IG(JPC)=0+(1-+)
½ (1-)
h’1 IG(JPC)=0+(1-+)
Both of these are lighter than expectations, and
The h[h’]p decay modes are not what are expected.
May 22, 2003
Curtis A. Meyer
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Interpretation
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qq
A recent paper by A. Szczepaniak explains the hp and h’p
as a background meson-meson interaction.
- Fits the E852 data, with the background similar to pp.
Is the p1(1400) a 4-quark object?
Is the p1(1600) the lightest hybrid?
- Recent lattice work indicates that it may be possible
to push the masses down.
May 22, 2003
Curtis A. Meyer
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Summary
qq
We have clear experimental evidence for
something outside of the simple
quark-antiquark picture of mesons.
How we interpret these signals is still an
open question.
New data with particular emphasis on
both I=0 states, and other exotic QN
states will be needed to solve this.
May 22, 2003
Curtis A. Meyer
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