1. Exotics as a Probe of Confinement
QCD Exotics – Past, Present and Future
Exotics as a Probe of Confinement
Curtis A. Meyer
Carnegie Mellon University
October 30, 2007
ODU Colloquium

2. Outline The beginning of time. The strong force and QCD
Color confinement
Spectroscopy
Lattice QCD
Finding Gluonic
Hadrons
Confinement
Outline
October 30, 2007
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3. The First Seconds
of The Universe
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4. Quark Gluon Plasma
For a period from about s to 10-6 s the universe
contained a plasma of quarks, anti quarks and gluons.
Relativistic Heavy Ion Collisions are trying to
produce this state of matter in collisions
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5. Confinement From about 10-6 s on, the quark and anti quarks became
confined inside of Hadronic matter. At the age of 1s,
only protons and neutrons remained.
The gluons produce
the 16ton force that
holds the hadrons
together.
Mesons
Baryons
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6. The Formation of Nuclei
By the old age of three minutes, the formation of low
mass nuclei was essentially complete.
Primordial hydrogen, deuterium, helium and a
few other light nuclei now exist.
It will be nearly a half a million years before
neutral atoms will dominate matter.
October 30, 2007
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7. Dynamics Quantum Chromo The rules that govern how the quarks
froze out into hadrons are given by QCD.
Just like atoms are
electrically neutral,
hadrons have to be
neutral.
Color Charge
Three charges called RED, BLUE and
GREEN, and three anti colors. The
objects that form have to be color
neutral:
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8. Gluons Carry the Force Meson Meson G R R G B Time
The exchange of gluons
is continually changing the
Individual colors of the
quarks, but the overall
Color remains neutral
Meson G R R G B
Time
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9. Gluons Carry the Force Meson Meson G R Time R G B
The exchange of gluons
is continually changing the
Individual colors of the
quarks, but the overall
Color remains neutral
Meson G R
Time R G B
October 30, 2007
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10. Gluons Carry the Force Meson Meson G R Time R G B
The exchange of gluons
is continually changing the
Individual colors of the
quarks, but the overall
Color remains neutral
Meson G R
Time R G B
Gluons produce the forces that
confine the quarks, but the gluons
do not appear to be needed to
understand normal hadrons
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11. Gluon Interactions G R R G B R G B 8 Gluons 3 Colors 3 Anti Colors
1 color neutral
8 colored objects
self-interaction of gluons
leads to both interesting
behavior of QCD, and its
extreme complications.
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12. Flux Tubes
October 30, 2007
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13. Flux Tubes
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
October 30, 2007
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14. Quark Confinement quarks can never be isolated
linearly rising potential
separation of quark from antiquark takes an infinite amount of energy
gluon flux breaks, new quark-antiquark pair produced
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15. Strong QCD See and systems. Color singlet objects observed in nature:
white
Nominally, glue is
not needed to
describe hadrons.
Focus on “light-quark mesons”
quark-antiquark states
glueballs
hybrids
Allowed systems: , ,
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16. Spectroscopy Positronium A probe of QED e+ e- Spin: S=S1+S2=(0,1)
Orbital Angular Momentum: L=0,1,2,…
Total Spin: J=L+S
L=0, S=0 : J=0 L=0, S=1 : J=1
L=1 , S=0 : J=1 L=1, S=1 : J=0,1,2
… …
Reflection in a mirror:
Parity: P=-(-1)(L)
Particle<->Antiparticle:
Charge Conjugation: C=(-1)(L+S)
Notation: J(PC) , 1--, 1+-, 0++, 1++, 2++
(2S+1)LJ S0, 3S1, 1P1, 3P0, 3P1, 3P2,…
October 30, 2007
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17. Quarkonium Spectroscopy and QCD Mesons q 9 Combinations
radial
Consider the three lightest quarks
9 Combinations
0-+
1+-
1--
0++
1++
2++
2-+
2--
3--
4++
3++
3+-
S=1
S=0
L=0
L=1
L=2
L=3
October 30, 2007
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18. Quarkonium Spectroscopy an QCD Mesons q r,K*,w,f Mesons come in
0-+
1+-
1--
0++
1++
2++
2-+
2--
3--
4++
3++
3+-
S=1
S=0
L=0
L=1
L=2
L=3
r,K*,w,f
Mesons come in
Nonets of the same
JPC Quantum Numbers
p,K,h,h’
a,K,f,f’
b,K,h,h’
SU(3) is broken
Last two members mix
r,K*,w,f
p,K,h,h’
October 30, 2007
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19. Quantum Mechanical Mixing
States with the same quantum numbers mix:
SU(3)
physical
states
Ideal Mixing:
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20. Quarkonium Quarkonium
Spectroscopy an QCD
Quarkonium
Quarkonium
Mesons q
Nothing to do
with Glue!
0-+
1+-
1--
0++
1++
2++
2-+
2--
3--
4++
3++
3+-
S=1
S=0
L=0
L=1
L=2
L=3
Allowed JPC Quantum numbers:
1-+
2+-
3-+
4+-
5-+ 1–
Exotic Quantum Numbers
non quark-antiquark description
October 30, 2007
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21. Glueball Predictions Particles that only contain gluons
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
2 + +
0 – +
2 – +
All of these are normal
quark-antiquark quantum
numbers.
Glueballs
0 + +
October 30, 2007
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22. Lattice QCD Predictions
Gluons can bind to form glueballs
EM analogue: massive globs
of pure light.
Lattice QCD predicts masses
The lightest glueballs have
“normal” quantum numbers.
Glueballs will Q.M. mix
The observed states will
be mixed with normal
mesons.
Strong experimental evidence
For the lightest state.
October 30, 2007
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23. Identification of Glueballs
Lightest Glueball predicted near two states of same Q.N..
“Over population” Predict 2, see 3 states
Glueballs should decay in a flavor-blind fashion.
Production Mechanisms:
Certain are expected to by Glue-rich, others are
Glue-poor. Where do you see them?
Proton-antiproton
Central Production
J/y decays
October 30, 2007
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24. Crystal Barrel Results
Crystal Barrel Results: antiproton-proton annihilation at rest
f0(1500) a pp, hh, hh’, KK, 4p
Discovery of the f0(1500)
Solidified the f0(1370)
f0(1370) a 4p
Establishes the scalar nonet
Crystal Barrel Results
Discovery of the a0(1450)
250,000 hhp0 Events
700,000 p0p0p0 Events
f2(1565)+s
f0(1500)
f2(1270)
f0(980)
f0(1500)
October 30, 2007
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25. Wa102 Results CERN experiment colliding p on a hydrogen target.
Central Production Experiment
Recent comprehensive data set
and a coupled channel analysis.
October 30, 2007
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26. A Model for Mixing meson 1 meson Glueball r2 meson Glueball r3
flavor blind? r
Solve for mixing scheme
F.Close: hep-ph/
October 30, 2007
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27. Experimental Evidence
Glueballs
Scalar (0++) Glueball and two
nearby mesons are mixed.
f0(980)
f0(1500)
f0(1370)
f0(1710)
a0(980)
a0(1450)
K*0(1430)
Glueball
spread
over 3
mesons
Are there other glueballs?
October 30, 2007
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28. Higher Mass Glueballs?
Part of the BES-III program will be to search for
glueballs in radiative J/ decays.
Lattice predicts that the 2++ and the 0-+ are the
next two, with masses just above 2GeV/c2.
Radial Excitations of the 2++ ground state
L= States + Radial excitations
f2(1950), f2(2010), f2(2300), f2(2340)…
2’nd Radial Excitations of the  and ’,
perhaps a bit cleaner environment! (I would
Not count on it though….)
I expect this to be very challenging.
October 30, 2007
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29. Hybrid Meson Predictions
qqg
Flux-tube model: 8 degenerate nonets
1++, ,0+-,1-+,1+-,2-+,2+- ~1.9 GeV/c2
S=0
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
exotic
nonets
0 – +
0 + –
1 + +
1 + –
1– +
1 – –
2 – +
2 + –
Hybrids
S=1
Start with S=0
1++ & 1--
Start with S=1
0-+ & 0+-
1-+ & 1+-
2-+ & 2+-
October 30, 2007
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30. QCD Potential ground-state excited flux-tube flux-tube m=1 m=0
linear potential
ground-state
flux-tube
m=0
excited flux-tube
m=1
Gluonic Excitations provide an
experimental measurement of
the excited QCD potential.
Observations of the nonets on the excited potentials are
the best experimental signal of gluonic excitations.
October 30, 2007
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31. Hybrid Predictions Flux-tube model: 8 degenerate nonets
1++, ,0+-,1-+,1+-,2-+,2+- ~1.9 GeV/c2
S=0
S=1
Lattice calculations nonet is the lightest
UKQCD (97) 0.20
MILC (97) 0.30
MILC (99) 0.10
Lacock(99) 0.20
Mei(02) 0.10
Bernard(04) §0.139
/- 0.2
/- 0.11
/- 0.6
In the charmonium sector:
0.08
0.11
Splitting = 0.20
October 30, 2007
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32. Looking for Hybrids Decay Predictions Analysis Method
Meson
Decay Predictions
Analysis Method
Partial Wave Analysis
Lglue
Fit n-D angular distributions
Fit Models of production and
decay of resonances.
Angular momentum
in the gluon flux stays confined.
This leads to complicated
multi-particle final states.
Detector needs to be
very good.
October 30, 2007
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33. Experimental Evidence
Hybrids
New York Times,
Sept. 2, 1997
Exotic Mesons
mass 1.4
E852 BNL ’97
CBAR CERN ’97
Too light
Not Consistent
Possible rescattering (?)
Decays are wrong (?)
Not a Hybrid
October 30, 2007
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34. E852 Results At 18 GeV/c to partial wave analysis suggests
October 30, 2007
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35. understood acceptance
An Exotic Signal
Correlation of
Phase
&
Intensity
Exotic
Signal
p1(1600)
Leakage
From
Non-exotic Wave
due to imperfectly
understood acceptance
3p m= G=
ph’ m= G=
October 30, 2007
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36. In Other Channels E852 Results
p-p  ’-p at 18 GeV/c
The 1(1600) is the
Dominant signal in ’.
Mass = 1.597 GeV
Width = 0.3400.040 GeV
1(1600)  ’
October 30, 2007
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37. In Other Channels E852 Results
1-+ in f1 and b1
p-p  +--p
p-p  w0-p
1(1600)  b1
1(1600)  f1
Mass=1.709 GeV
Width=0.4030.08 GeV
In both b1 and f1, observe
Excess intensity at about
2GeV/c2.
Mass ~ 2.00 GeV,
Width ~ 0.2 to 0.3 GeV
Mass = 1.687 GeV
Width = 0.2060.03 GeV
October 30, 2007
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38. New Analysis 10 times statistics in Add 2(1670)-> (L=3)
Dzierba et. al. PRD 73 (2006)
Add 2(1670)-> (L=3)
Add 2(1670)->3
Add 2(1670)-> ()S
Add a3 decays
Add a4(2040)
10 times statistics in
each of two channels.
Get a better description
of the data via moments
comparison
No Evidence for the 1(1670)
October 30, 2007
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39. Exotic Signals 1(1400) Width ~ 0.3 GeV, Decays: only 
weak signal in p production (scattering??)
strong signal in antiproton-deuterium.
NOT A
HYBRID
Does
this
exist?
1(1600) Width ~ 0.16 GeV, Decays ,’,(b1)
Only seen in p production, (E852 + VES)
1(2000) Weak evidence in preferred hybrid
modes f1 and b1
The right
place. Needs
confirmation.
p1 IG(JPC)=1-(1-+)
h’1 IG(JPC)=0+(1-+)
h1 IG(JPC)=0+(1-+)
K1 IG(JPC)= ½ (1-)
October 30, 2007
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40. Experimental Evidence
New York Times,
Sept. 2, 1997
Hybrid Nonets
1-+
Establish other Nonets:
Levels
Built on normal mesons
Identify other
states in nonet
to establish hybrid
October 30, 2007
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41. Jefferson Lab Upgrade
October 30, 2007
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42. Upgrade magnets and power supplies
Jefferson Lab Upgrade
CHL-2
Upgrade magnets and power supplies
October 30, 2007
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43. The GlueX Experiment
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44. How to Produce Hybrids Beams of photons may be a more natural
way to create hybrid mesons.
Simple QN counting leads to the exotic mesons
There is almost no data for photon beams at
these energies. GlueX will increase samples by
3-4 orders of magnitude.
October 30, 2007
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45. This technique provides requisite energy, flux and polarization
Coherent
Bremsstrahlung
12 GeV electrons
Incoherent &
coherent spectrum
flux
This technique provides requisite energy, flux and polarization
tagged
with 0.1% resolution
40%
polarization
in peak
Linearly polarized
photons out
collimated
electrons in
spectrometer
diamond
crystal
photon energy (GeV)
October 30, 2007
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46. Exotics g  ,, In Photoproduction 1-+ nonet p1 IG(JPC)=1-(1-+)
h’1 IG(JPC)=0+(1-+)
h1 IG(JPC)=0+(1-+)
K1 IG(JPC)= ½ (1-) N g e X
g  ,,
Need to establish nonet nature
of exotics:   0
Need to establish more than one
nonet:
October 30, 2007
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47. Gluonic Hadrons and Confinement
What are the light quark
Potentials doing? DE
Lattice QCD potentials
Potentials corresponding
To excited states of glue.
Non-gluonic mesons –
ground state glue.
October 30, 2007
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48. Conclusions The quest to understand confinement
and the strong force is about to make
great leaps forward.
Advances in theory and computing
will soon allow us to solve QCD
and understand the role of glue.
The definitive experiments to
confirm or refute our expectations
are being built.
The synchronized advances in both areas will allow
us to finally understand QCD and confinement.
October 30, 2007
ODU Colloquium