An Experimental

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An Experimental
Overview of Gluonic Mesons
Curtis A. Meyer Carnegie Mellon
University May 14, 2003
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Talk Outline
What are gluonic excitations ? Hybrids
and Glueballs Overview of evidence for exotic
quantum number states. Non-exotic quantum
number states. Overview of Glueballs.
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Normal Mesons
Non-quark-antiquark 0-- 0- 1- 2- 3-
quark-antiquark pairs
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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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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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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
? 0.50
In the charmonium sector 1- 4.39 ?0.08 0-
4.61 ?0.11
Splitting 0.20
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Decays of Hybrids
The angular momentum in the flux tube stays in
one of the daughter mesons (L1) and (L0)
meson.
Exotic Quantum Number Hybrids
?1? ?b1 , ?f1 , ?? , ?a1
1.25.25.20 h1?p(1300)p , a1p
11 b2 ? a1p , h1p , wp , a2p
110.50.25 h2 ? b1p , rp , wh
110.1 b0 ? p(1300)p , h1p
10.20 h0 ? b1p , h1h
10.02
Mass and model dependent predictions
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Glueball Mass Spectrum
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
Proton-Antiproton Annihilation
0 f0(1370),f0(1500)
Central Production (double-pomeron exchange)
0 f0(1370),f0(1500), f0(1710)
Glueballs should decay in a flavor-blind fashion.
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E852 Results
Exotic Quantum Numbers 1- in ??
Mass 1370 -1650-30 MeV/c2 Width 385
- 4065-105 MeV/c2
p-p -gt hp- p
p1(1400)
(18 GeV)
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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Crystal Barrel
Exotic Quantum Numbers 1- in ??
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
Exotic Quantum Numbers 1- in ??
At 18 GeV/c
suggests
to partial wave analysis
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E852 Results
Exotic Quantum Numbers 1- in ??
Exotic Signal
p1(1600)
3p m1593-828-47 G168-20150-12
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E852 Results
Exotic Quantum Numbers 1- in ??
p-p ? ??-p at 18 GeV/c
The ?1(1600) is the Dominant signal in ??. Mass
1.597?0.010 GeV Width 0.340?0.040 GeV
?1(1600) ? ??
Other reports here
?1(1600) ? b1?
?1(1600) ? f1?
rp , b1? , f1? , ??
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VES Results
Exotic Quantum Numbers 1- in rp, b1p and ??
m1.6?0.02 GeV/c2 G0.29?0.03 GeV/c2
?1(1600) observed in pA reactions
b1p hp rp 1 1.0?0.3 1.6 ?0.4
b1p (1-)
?-A???? (A) (at 37 GeV/c)
Phase wrt 2
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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 0.16 to 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 ?h? decay modes are not what are
expected.
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
1st radial excitation
a1,f1,f1,K1
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
L2 orbital excitation
1st/2nd radial excitation
r,w,f,K
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
2nd radial excitation
p,h,h,K
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
1st radial excitation
b1,h1,h1,K1
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
L2 orbital excitation plus radial
p2,h2,h2,K2
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Hybrid Mesons
with normal QNs
Assume that ?1(1600) sets the mass scale
Non-exotic hybrid QNs
p2,h2,h2,K2
a1,f1,f1,K1
b1,h1,h1,K1
r,w,f,K
p,h,h,K
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The 1 Mesons
1 1st Radial Excitation of a1(1260)/f1(1285)
m1.64?0.05 GeV/c2 G0.30 ?0.1 GeV/c2
a1(1640)
Decays to 3p via f2p and (pp)Sp
Consistent with a normal meson
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The 1-- Mesons
1-- 1st Radial Excitation of ?/?. 2nd
Radial Excitation of ?/?. L2 D-wave
(?1, ?2, ?3)
r3(1690) w3(1670) f3(1850)
f(1680)
w(1420)
r(1450)
L2 Scale
w(1650)
r(1700)
r(1900)
r(2150)
Decay modes are significant here, but data is
hard to interpret.
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The 0- Mesons
m1.801?0.013 GeV/c2 G0.210 ?0.015 GeV/c2
p(1800)
Decays f0(980)p, f0(1370)p, rp, hhp, a0(980)h,
f0(1500)p
Speculation that this may be a hybrid
h(1760)
Produced in J/?, decays to 4?
m2.230?0.050 GeV/c2 G0.150 ?large GeV/c2
h(2225)
Glueball quantum numbers
Produced in J/?, decays to ff
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The 1- Mesons
1- 1st Radial Excitation of the
b1(1235)/h1(1170)
m1.594?0.05 GeV/c2 G0.384 ?0.15 GeV/c2
h1(1595)
Produced in pp interactions Decays to wh
Consistent with a normal meson ?
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The 2- Mesons
m1.67?0.02 GeV/c2 G0.259 ?0.001 GeV/c2
?2(1670)
Decays f2p, rp, (pp)Sp, fo(1370)p, KK (f2p is
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m1.617?0.005 GeV/c2 G0.181 ?0.011 GeV/c2
h2(1645)
Decays a2p, KKp, aop (a2p is largest)
m1.842?0.008 GeV/c2 G0.225 ?0.014 GeV/c2
h2(1870)
Hybrid Candidate?
Decays a2p, f2h, aop (a2p is largest)
m2.090?0.030 GeV/c2 G0.625 ?0.100 GeV/c2
?2(2100)
Decays f2p, rp, (pp)Sp
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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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Crystal Barrel
Results on Scalars
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)
s
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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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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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. (Just
approved by the German government.)
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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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Strong QCD
Color singlet objects observed in nature
Quarks in 3 colors
8 Gluons carry color anticolor
Focus on light-quark mesons
Glueballs Hybrids 4-quark
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Nonet Mixing
The I0 members of a nonet can mix
SU(3)
physical states
Ideal Mixing
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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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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
The Scalar Mesons
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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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.