Why QCD

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Why QCD

• Predicts existence of matter made from
  radiation (glueballs) or hybrid matter.

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.. and the reasons are

• relativistic, quantum, many-body system
• (local quantum field theory)

• unphysical degrees of freedom
• (gauge symmetry)

• cannot be rigorously defined before it is solved
  
• (renormalization)

• the interaction is strong
• (confinement)

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and relativistic (Lorentz) boosts mix different
components
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Self similarity and renormalization
length scale size of
g0 g(a0) is undetermined
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Confinement
r
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There are different stories
Story 1 (Gell-Mann, Zweig)
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Story 2 (Feynman)
Asymptotic freedom QCD interactions become
weak at short distances
In the 1 momentum frame proton looks like a
collection of free partons
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Story 2 (cont.)
Partons quarks gluons
Momentum fraction distribution
quark
antiquark
glue
xmomentum of gluons/ptoton momentum
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Canonical QCD in the Coulomb gauge

• Leads to quasi-particle (constituent)
  representation
• Hadron i Valence quarks i
  small corrections

• Natural for non-relativistic systems (EM,QM)

• Amendable to standard many-body techniques
• (finite temperature and/or density)

• Emission and/or absorption of colored gluons
  (radiation)
• is separated from (instantaneous) Coulomb
  interaction
• natural realization of
  Confinement

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• Gluons role in confinement, formation of the
• constituent quarks and residual
  interactions

(Indirect)
2. Gluons role in determining hadron structure
(Direct)
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Confinement Lattice simulation
Ansatz wave function
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Where do constituent quarks come from
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Effective mass of a constituent quark
(Szczepaniak,Krupinski (02))
h mq(k) i GeV
With transverse gluons
Without transverse gluons
k GeV
Uses liked cluster expansion (BCS 3 particle
clusters)
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Indirect evidenced (summary)
Coulomb (static) gluons ! confining interaction
Radiation effects are suppressed ! residual
interactions (multipole expansion)
(e.g. hyperfine)
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Direct evidence for gluonic excitation
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Glueballs
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Crystal Barrel
Evidence for f0(1500) Scalar Glueball
m2(p0 p0) GeV2
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Glueballs from QCD
SpinParity, Charge Conjugation JPC
M M ( JPC )
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• and we want
• clean resonances (peak phase motion)
• overpopulation

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Exotic hybrids
JPC 0- , 1-- , 1-, L
JPC 1-, 0--, 0-, L
h Meson Exotic Mesons i 0 !
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Has implications for exotic meson decays
simple decay modes (e.g. ph) are suppressed
( Swanson, Szczepaniak (99) )
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Light exotic meson
Lattice predictions
Lacock Schilling

• JPC 1- lowest state
• Higher masses difficult to resolve
• Chiral extrapolations 100-200 MeV

Thomas, Szczepaniak (02)
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Decays

• Normal widths !

In large NC same as for ordinary mesons O(1/NC)
Cohen (98)

• Unusual decay modes !

IKP Isgur, Kokosky, Paton (85) PSS Page,
Swanson, Szczepaniak (99)

• Low lying states expected
• below string breaking !

Morningstar (99) Bali (00)
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• Current phenomenology

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Is there an hp P-wave exotic 1- quantum
numbers ?
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Summary of hp0 and hp- experimental results

• The a0(980) and a2(1320) are clearly seen.
• The Breit-Wigner parameterization reproduces
  PDG values
• and production mechanisms are well understood.

• However it cannot be
• unambiguously described as
• a simple Breit-Wigner resonance
• The question remains
• what is the nature of this wave.
• .

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h-p0 P-wave phase shift
qhp MeV/c
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Finding the Exotic Wave
Double-blind M. C. exercise
An exotic wave (JPC 1-) was generated at level
of 2.5 with 7 other waves. Events were smeared,
accepted, passed to PWA fitter.
Statistics shown here correspondto a few days of
running.