Gluonic Excitations of

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Gluonic Excitations of
Hadrons
Curtis A. Meyer Carnegie Mellon
University February 7, 2003
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Outline of Talk

• Introduction
• Meson Spectroscopy
• Glueballs
• Expectations
• Experimental Data
• Interpretation
• Hybrid Mesons
• Expectations
• Experimental Data
• Interpretation
• The Future

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QCD
is the theory of quarks and gluons
3 Colors 3 Anti-colors
8 Gluons, each of which has a color an an
anti-color Charge.
Six Flavors of quarks
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Jets at High Energy
Direct evidence for gluons come from high
energy jets. But this doesnt tell us anything
about the static properties of glue. We learn
something about ?s
2-Jet
3-Jet
gluon bremsstrahlung
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Deep Inelastic Scattering
As the nucleon is probed to smaller and smaller
x, the gluons become more and more important.
Much of the nucleon momentum and most of its spin
is carried by gluons!
Glue is important to hadronic structure.
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Strong QCD
Color singlet objects observed in nature
Nominally, glue is not needed to describe
hadrons.
Focus on light-quark mesons
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Normal Mesons
Non-quark-antiquark 0-- 0- 1- 2- 3-
quark-antiquark pairs
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Nonet Mixing
The I0 members of a nonet can mix
SU(3)
physical states
Ideal Mixing
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Spectrum
Each box corresponds to 4 nonets (2 for L0)
Radial excitations
Lattice 1- 1.9 GeV
0 1.6 GeV
(L qq angular momentum)
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Glueball Mass Spectrum
QCD is a theory of quarks and gluons
What role do gluons play in the meson spectrum?
Lattice calculations predict a spectrum of
glueballs. The lightest 3 have JPC Quantum
numbers of 0 , 2 and 0-. The lightest is
about 1.6 GeV/c2
f0(1710)
f0(1500)
a0(1450)
K0(1430)
f0(1370)
Morningstar et al.
a0(980)
f0(980)
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Glue-rich channels
Where should you look experimentally for
Glueballs?
Radiative J/? Decays
0- ?(1440) 0 f0(1710)
Large signals
Proton-Antiproton Annihilation
Central Production (double-pomeron exchange)
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Decays of Glueballs?
Glueballs should decay in a flavor-blind fashion.
??0 is true for any SU(3) singlet and for any
pseudoscalar mixing angle. Only an SU(3)
8 can couple to ??.
Flavor-blind decays have always been cited as
glueball signals.
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Crystal Barrel Results
Crystal Barrel Results antiproton-proton
annihilation at rest
f0(1500) a pp, hh, hh, KK, 4p
Discovery of the f0(1500)
f0(1370) a 4p
Solidified the f0(1370)
Establishes the scalar nonet
Discovery of the a0(1450)
250,000 hhp0 Events
700,000 p0p0p0 Events
f2(1565)s
f0(1500)
f2(1270)
f0(980)
f0(1500)
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The f0(1500)
Is it possible to describe the f0(1500) as a
member of a meson nonet?
Use SU(3) and OZI suppression to
compute relative decays to pairs of pseudoscalar
mesons
Get an angle of about 143o
90 light-quark 10 strange-quark
Both the f0(1370) and f0(1500) are
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WA102 Results
CERN experiment colliding p on a hydrogen target.
Central Production Experiment
Recent comprehensive data set and a coupled
channel analysis.
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Model for Mixing
1
r2
r3
flavor blind? r
Solve for mixing scheme
F.Close hep-ph/0103173
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Meson Glueball Mixing
Physical Masses f0(1370),f0(1500),f0(1710)
Bare Masses m1,m2,mG
(G) (S)
(N) f0(1370) -0.69?0.07 0.15?0.01
0.70?0.07 f0(1500) -0.65?0.04 0.33?0.04
0.70?0.07 f0(1710) 0.39?0.03 0.91?0.02
0.15?0.02
octet piece
m11377?20 m21674?10 mG1443?24
Lattice of about 1600
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Glueball Expectations
Antiproton-proton Couples to
Observe f0(1370),f0(1500)
Central Production Couples to G and
in phase. Observe f0(1370),f0(1500),
weaker f0(1710).
Radiative J/? Couples to G, 1gt, suppressed 8gt
Observe strong f0(1710) from constructive
1gtG Observe f0(1500) from G Observe weak
f0(1370) from destructive 1gtG
Two photon Couples to the quark content of
states, not to the
glueball. Not clear to me that
has been seen.
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Higher mass glueballs?
Part of the CLEO-c 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 L3
2 States Radial excitations f2(1950),
f2(2010), f2(2300), f2(2340)
2nd Radial Excitations of the ? and ?, perhaps
a bit cleaner environment! (I would Not count on
it though.)
I expect this to be very challenging.
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Lattice QCD
Flux Tubes Realized
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
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Hybrid Mesons
built on quark-model mesons
1- or 1-
normal mesons
CP(-1)LS(-1)L1 (-1)S1
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QCD 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.
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Hybrid Predictions
Flux-tube model 8 degenerate nonets
1,1-- 0-,0-,1-,1-,2-,2- 1.9 GeV/c2
S0
S1
Lattice calculations --- 1- nonet is the
lightest UKQCD (97) 1.87 ?0.20 MILC (97)
1.97 ?0.30 MILC (99) 2.11
?0.10 Lacock(99) 1.90 ?0.20 Mei(02)
2.01 ?0.10
2.0 GeV/c2
1- 0- 2-
Splitting ? 0.20
In the charmonium sector 1- 4.39 ?0.08 0-
4.61 ?0.11
Splitting 0.20
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Decays of Hybrids
Decay calculations are model dependent, but the
3P0 model does a good job of describing normal
meson decays.
0 quantum numbers (3P0)
The angular momentum in the flux tube stays in
one of the daughter mesons (L1) and (L0) meson.
L0 ?,?,?,?, L1 a,b,h,f,
??,??, not preferred.
?1??b1,?f1,??,?a1 87,21,11,9 MeV (partial
widths)
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E852 Results
p-p -gt hp- p
(18 GeV)
Mass 1370 -1650-30 MeV/c2 Width 385
- 4065-105 MeV/c2
p1(1400)
The a2(1320) is the dominant signal. There is a
small (few ) exotic wave.
p1
a2
Interference effects show a resonant structure in
1- . (Assumption of flat background phase as
shown as 3.)
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CBAR Exotic
Crystal Barrel Results antiproton-neutron
annihilation
Same strength as the a2.
Mass 1400 - 20 - 20 MeV/c2 Width
310-5050-30 MeV/c2
Produced from states with one unit of angular
momentum.
p1(1400)
Without p1 c2/ndf 3, with 1.29
hp0p-
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Significance of signal.
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E852 Results
At 18 GeV/c
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An Exotic Signal
Exotic Signal
p1(1600)
3p m1593-828-47 G168-20150-12 ph
m1597-1045-10 G340-40-50
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Exotic Signals
?1(1400) Width 0.3 GeV, Decays only ??
weak signal in ?p production (scattering??)
strong signal in antiproton-deuterium.
?1(1600) Width 0.3 GeV, Decays ??,??,(b1?)
Only seen in ?p production, (E852 VES)
In a nonet, there should only be one ?1 state.
Both of these are lighter than expectations,
and The decay modes are not what is expected.
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Photoproduction
of Exotics
Quark spins anti-aligned
A pion or kaon beam, when scattering occurs, can
have its flux tube excited
Much data in hand with some evidence for gluonic
excitations (tiny part of cross section)
_
_
_
_
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Exotics
in Photoproduction
1- nonet
g ? ?,?,?
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0- and 2- Exotics
In photoproduction, couple to r, w or f?
?a1,?f0,?f1
wf0,wf1,ra1
ff0,ff1,ra1
wp, ?a1,?f0,?f1
wh,rp,wf0,wf1,ra1
Similar to p1
fh,rp,ff0,ff1,ra1
Kaons do not have exotic QNs
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Exotics and QCD
In order to establish the existence of gluonic
excitations, We need to establish the nonet
nature of the 1- state. We need to establish at
other exotic QN nonets the 0- and 2-.
In the scalar glueball sector, the decay patterns
have provided the most sensitive information. I
expect the same will be true in the hybrid
sector as well.
DECAY PATTERS ARE CRUCIAL
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The Scalar Mesons
The Scalar Mesons
Overpopulation Strange Decay Patterns Seen in
glue-rich reactions Not in glue-poor
What about 2 and 0- ?
J/Y Decays?
Glueball and Mesons are mixed. Scheme is model
dependent.
Awaiting CLEO-c
Crystal Barrel proton-antiproton annihilation
Central Production WA102
Three States f0(1370) f0(1500) f0(1710)
0 rr
0 ss
1.5
2.5
2.5
1.5
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What will we learn?
There is an clear signal for hybrid mesons
Exotic quantum numbers but confirmation
requires the observation of a nonet, not just a
single state. Mapping out more than one exotic
nonet is necessary to Establishing the hybrid
nature of the states. Decay patterns will be
useful for the exotic QN states, And necessary
for the non-exotic QN states.
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Summary
The first round of J/? experiments opened the
door to exotic spectroscopy, but the results were
confused.
LEAR at CERN opened the door to precision,
high-statistics spectroscopy experiments and
significantly improved both our understanding of
the scalar mesons and the scalar glueball.
Pion production experiments at BNL (E852) and
VES Opened the door to states with
non-quark-anti-quark Quantum numbers.
CERN central production (WA102) provided solid
new data on the scalar sector, and a deeper
insight into the scalar glueball.
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The Future
The CLAS experiment at Jefferson Lab is opening
a small window to meson spectroscopy in
photoproduction.
CLEO-c will reopen the J/? studies with 100
times Existing statistics. One goal is to find
and study the Pseudoscalar (0-) and tensor
glueball (2)
The GlueX experiment will be able to do for
hybrids what Crystal Barrel and WA102 (together)
did for glueballs. What are the properties of
static glue in hadrons and how is this connected
to confinement.
The antiproton facility at GSI (HESR) will look
for hybrids in the charmonium system.
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Gluonic Excitations
Workshop at JLab May 14-16, 2003.