May 31, 2006 CIPANP 20061
Glueballs, Hybrids & Exotics
Curtis A. MeyerCarnegie Mellon University May 31, 2006
An Experimental & Phenomenological Overview
May 31, 2006 CIPANP 20062
Outline of Talk
• Introduction• Meson Spectroscopy• Glueballs
• Expectations• Experimental Data• Interpretation
• Hybrid Mesons• Expectations• Experimental Data• Interpretation
•The Future
LS
S
1
2
S = S + S1 2
J = L + S
C = (-1)L + S
P = (-1)L + 1
May 31, 2006 CIPANP 20063
Strong QCD
See and systems.qq qqq
white
white
Color singlet objects observed in nature:
Allowed systems: , , ggggg, gqq qqqq
Nominally, glue isnot needed to describe hadrons.
s
d
u
s
d
u
Focus on “light-quark mesons”
May 31, 2006 CIPANP 20064
quark-antiquark pairs
ud
s u d
s
J=L+S
P=(-1) L+1
C=(-1) L+S
G=C (-1) I
(2S+1) L J
1S0 = 0 -+
3S1 = 1--,K*’,KL=0
1--
0-+
a2,f2,f’2,K2
a1,f1,f’1,K1
a0,f0,f’0,K0
b1,h1,h’1,K1
L=1
2++
1++
0++
1+-
3,3,3,K3
2,2,2,K2
1,1,1,K1
2,2,’2,K2
L=2
3--
2--
1--
2-+
radial
orbital
Non-quark-antiquark0-- 0+- 1-+ 2+- 3-+ …
Normal Mesons
May 31, 2006 CIPANP 20065
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
Each box correspondsto 4 nonets (2 for L=0)
Radial excitations
(L = qq angular momentum)
exoticnonets
0 – +
0 + –
1 + +
1 + –
1– +
1 – –
2 – +
2 + –2 + +
0 – +
2 – +
0 + +
Glueballs
Hybrids
Lattice 1-+ 1.9 GeV
Spectrum
0++ 1.6 GeV
May 31, 2006 CIPANP 20066
QCD is a theory of quarks and gluons
What role do gluons play in the mesonspectrum?
Lattice calculations predict a spectrumof glueballs. The lightest 3 have JPC
Quantum numbers of 0++ , 2++ and0-+.
The lightest is about 1.6 GeV/c2
Morningstar et al.f0(980)
f0(1500)
f0(1370)
f0(1710)
a0(980)
a0(1450) K*0(1430)
Glueball Mass Spectrum
May 31, 2006 CIPANP 20067
Glue-rich channels
G
M
M Radiative J/ Decays
Proton-Antiproton Annihilation
Central Production (double-pomeron exchange)
Where should you look experimentally for Glueballs?
0-+ (1440)0++ f0(1710)
Large signals
May 31, 2006 CIPANP 20068
Decays of Glueballs?
Glueballs should decay in a flavor-blind fashion.
0:1:1:4:3':''::: KK
’=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. Not necessarily true.
May 31, 2006 CIPANP 20069
f0(1500)
f2(1270)
f0(980)
f2(1565)+700,000 000 Events
Crystal Barrel Results: antiproton-proton annihilation at rest
f0(1500)
250,000 0 Events
Discovery of the f0(1500) f0(1500) ’, KK, 4
f0(1370)
Crystal Barrel Results Establishes the scalar nonet
Solidified the f0(1370)
Discovery of the a0(1450)
May 31, 2006 CIPANP 200610
The f0(1500)
Is it possible to describe the f0(1500) as a memberof a meson nonet?
Use SU(3) and OZI suppression to computerelative decays to pairsof pseudoscalar mesons
8
1
cos
sin
sin
cos
)1500(
)1370(
0
0
f
f
Get an angle of about 143o
90% light-quark10% strange-quark
Both the f0(1370) and f0(1500) are dduu &
May 31, 2006 CIPANP 200611
WA102 Results
Central Production Experiment
)%90(05.0)1710(
')1710(
14.048.0)1710(
)1710(
03.020.0)1710(
)1710(
16.052.0)1500(
')1500(
07.032.0)1500(
)1500(
84.05.5)1500(
)1500(
21.035.0)1370(
)1370(
90.017.2)1370(
)1370(
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
clf
f
KKf
f
KKf
f
f
f
f
KKf
f
f
KKf
f
KKf
f
Recent comprehensive data setand a coupled channel analysis.
CERN experiment colliding pon a hydrogen target.
May 31, 2006 CIPANP 200612
BES Results XJ /
0 0
0 00 0
0 0
/ (1500) (1500)
/ (1500) (1500)
/ (1500) (1500)
J f f
J f f
J f f
0.665 10-4
0.34 10-4
3.1 10-4
0 0
0 00 0
0 0
0 0
/ (1710) (1710)
/ (1710) (1710)
/ (1710) (1710)
/ (1710) (1710)
J f f
J f f
J f f KK
J f f
2.64 10-4
1.33 10-4
9.62 10-4
3.1 10-4
Clear Production of f0(1500) and f0(1710), no reportof the f0(1370). f0(1710) has strongest production.
May 31, 2006 CIPANP 200613
Model for Mixing
meson
mesonGlueball
meson
mesonmeson
Glueballmeson
meson
1
r2
r3
qqG flavor blind? r
Solve for mixing scheme
ssdduu ,,
F.Close: hep-ph/0103173
May 31, 2006 CIPANP 200614
Meson Glueball MixingPhysical Massesf0(1370),f0(1500),f0(1710)
Bare Masses:m1,m2,mG
2
dduu
ss (G) (S) (N)f0(1370) -0.690.07 0.150.01 0.700.07f0(1500) -0.650.04 0.330.04 –0.700.07f0(1710) 0.390.03 0.910.02 0.150.02
m1=137720 m2=167410 mG=144324
octet piece
Lattice of about 1600
May 31, 2006 CIPANP 200615
Glueball Expectations
Antiproton-proton: Couples to Observe: f0(1370),f0(1500)
dduu
Central Production: Couples to G and in phase. Observe: f0(1370),f0(1500), weaker f0(1710).
dduu
Radiative J/: Couples to G, |1>, suppressed |8> Observe strong f0(1710) from constructive |1>+G Observe f0(1500) from G Observe weak f0(1370) from destructive |1>+G Two photon: Couples to the quark content of states, not to the glueball. Not clear to me that has been seen.0f
May 31, 2006 CIPANP 200616
Higher mass glueballs?
Lattice predicts that the 2++ and the 0-+ are the next two, with masses just above 2GeV/c2.
Radial Excitations of the 2++ ground stateL=3 2++ States + Radial excitationsf2(1950), f2(2010), f2(2300), f2(2340)…
2’nd Radial Excitations of the and ’,perhaps a bit cleaner environment! (I wouldNot count on it though….)
I expect this to be very challenging.
May 31, 2006 CIPANP 200617
m=0 CP=(-1) S+1
m=1 CP=(-1) S
Flux-tube Model
ground-state flux-tube m=0
excited flux-tube m=1
built on quark-model mesons
CP={(-1)L+S}{(-1)L+1} ={(-1)S+1}
S=0,L=0,m=1
J=1 CP=+
JPC=1++,1--
(not exotic)
S=1,L=0,m=1
J=1 CP=-JPC=0-+,0+-
1-+,1+-
2-+,2+-exotic
normal mesons
Hybrid Mesons
1-+ or 1+-
,,
May 31, 2006 CIPANP 200618
linear potential
ground-state flux-tube m=0
excited flux-tube m=1
Gluonic Excitations provide anexperimental measurement of the excited QCD potential.
Observations of exotic quantum number nonets are thebest experimental signal of gluonic excitations.
QCD Potential
May 31, 2006 CIPANP 200619
Hybrid Predictions
Flux-tube model: 8 degenerate nonets 1++,1-- 0-+,0+-,1-+,1+-,2-+,2+- ~1.9 GeV/c2
Lattice calculations --- 1-+ nonet is the lightest UKQCD (97) 1.87 0.20MILC (97) 1.97 0.30MILC (99) 2.11 0.10Lacock(99) 1.90 0.20Mei(02) 2.01 0.10
~2.0 GeV/c2
In the charmonium sector:1-+ 4.39 0.080+- 4.61 0.11
Splitting = 0.20
1-+
0+-
2+-
Splitting 0.20
S=0 S=1
May 31, 2006 CIPANP 200620
Decays of Hybrids
Decay calculations are model dependent, but the 3P0
model does a good job of describing normal mesondecays.
0++ quantum numbers (3P0)
The angular momentum in the flux tube stays in one ofthe daughter mesons (L=1) and (L=0) meson.L=0: ,,,,…L=1: a,b,h,f,…
,, … not preferred.
1b1,f1,,a1 87,21,11,9 MeV (partial widths)
May 31, 2006 CIPANP 200621
pp (18 GeV)
The a2(1320) is the dominantsignal. There is a small (few %)exotic wave.
Interference effects showa resonant structure in .(Assumption of flat backgroundphase as shown as 3.)
Mass = 1370 +-16+50
-30 MeV/c2
Width= 385 +- 40+65-105 MeV/c2
a2
E852 Results
May 31, 2006 CIPANP 200622
(1400)
Crystal Barrel Results: antiproton-neutron annihilation
Mass = 1400 +- 20 +- 20 MeV/c2
Width= 310+-50+50-30 MeV/c2
Same strength as the a2.
Produced from states with one unit
of angular momentum.Without 1 2/ndf = 3, with = 1.29
CBAR Exotic
May 31, 2006 CIPANP 200623
Controversy
In analysis of E852 ± data, so evidence of the 1(1400)
In CBAR data, the ± channel is not conclusive.
Analysis by Szczepaniak shows that the exotic wave is not resonant – a rescattering effect.
The signal is far too light to be a hybrid by any model.
This is not a hybrid and may well not be a state.
May 31, 2006 CIPANP 200624
p p
At 18 GeV/c
suggests p 0 p
p
to partial wave analysis
M( ) GeV / c2 M( ) GeV / c2
E852 Results
May 31, 2006 CIPANP 200625
An Exotic Signal
LeakageFrom
Non-exotic Wavedue to imperfectly
understood acceptance
ExoticSignal
1
Correlation ofPhase
&Intensity
M( ) GeV / c2
1(1600)
3 m=1593+-8+28-47 =168+-20+150
-12
’ m=1597+-10+45-10 =340+-40+-50
May 31, 2006 CIPANP 200626
-p ’-p at 18 GeV/c
The 1(1600) is the Dominant signal in ’.Mass = 1.5970.010 GeVWidth = 0.3400.040 GeV 1(1600) ’
E852 Results
In Other Channels
1-+ in ’
May 31, 2006 CIPANP 200627
-p +--p
1(1600) f1
E852 Results
-p 0-p 1(1600) b1
Mass = 1.6870.011 GeV
Width = 0.2060.03 GeV
Mass=1.7090.024 GeV
Width=0.4030.08 GeV
In both b1 and f1, observeExcess intensity at about2GeV/c2.Mass ~ 2.00 GeV, Width ~ 0.2 to 0.3 GeV
In Other Channels1-+ in f1 and b1
May 31, 2006 CIPANP 200628
1(1600) Consistency
3 m=1593 =1680 m=1597 =340f1 m=1709 =403b1 m=1687 =206
Not Outrageous, but not great agreement.Mass is slightly low, but not crazy.
Szczepaniak: Explains much of the 0 signalas a background rescattering similar to the
Still room for a narrower exotic state.
May 31, 2006 CIPANP 200629
New Analysis
Dzierba et. al. PRD 73 (2006)
Add 2(1670)! (L=3)Add 2(1670)!3Add 2(1670)! ()SAdd a3 decaysAdd a4(2040)
4-5 times statistics in 2each of two channels
Get a better descriptionof the data via momentscomparison
No Evidence for the 1(1670)
May 31, 2006 CIPANP 200630
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 GeV, Decays ,’,(b1) Only seen in p production, (E852 + VES)
1 IG(JPC)=1-(1-+)
’1 IG(JPC)=0+(1-+)
1 IG(JPC)=0+(1-+)
K1 IG(JPC)= ½ (1-)
1(2000) Weak evidence in preferred hybrid modes f1 and b1
NOT AHYBRID
Doesthis exist?
The rightplace. Needsconfirmation.
May 31, 2006 CIPANP 200631
Photoproduction
of Exotics
A pion or kaon beam, when scattering occurs,
can have its flux tube excitedor
beam
Quark spins anti-aligned
Much data in hand with some evidence for gluonic excitations
(tiny part of cross section)
q
q
befo
req
qaft
er
q
q
aft
er
q
q
befo
re
beamAlmost no data in hand
in the mass regionwhere we expect to find exotic hybrids
when flux tube is excited
Quark spins aligned
__
__
May 31, 2006 CIPANP 200632
Exotics
N N
e
X
,,
1 IG(JPC)=1-(1-+)
’1 IG(JPC)=0+(1-+)
1 IG(JPC)=0+(1-+)
K1 IG(JPC)= ½ (1-)
1-+ nonet
in Photoproduction
Need to establish nonet nature of exotics: 0
Need to establish more than onenonet: 0+- 1-+ 2+-
May 31, 2006 CIPANP 200633
0+- and 2+- Exotics
N N
e
X
b0 IG(JPC)=1+(0+-)
h0 IG(JPC)=0-(0+-)
h’0 IG(JPC)=0-(0+-)
K0 I(JP)=½(0+)
b2 IG(JPC)=1+(2+-)
h2 IG(JPC)=0-(2+-)
h’2 IG(JPC)=0-(2+-)
K2 I(JP)= ½(2+)
a1,f0,f1
f0,f1,a1
f0,f1,a1
, a1,f0,f1
f0,f1,a1
f0,f1,a1
In photoproduction, couple to , or ?
“Similar to 1 ”
Kaons do not have exotic QN’s
May 31, 2006 CIPANP 200634
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 sensitiveinformation. I expect the same will be true in the hybrid sector as well.
DECAY PATTERS ARE CRUCIAL
May 31, 2006 CIPANP 200635
The Scalar Mesons
1.5
0++
2.5 2.51.5
0++
Central Production WA102Three States f0(1370)f0(1500)f0(1710)
OverpopulationStrange Decay PatternsSeen in glue-rich reactionsNot in glue-poor
Glueball and Mesonsare mixed. Scheme ismodel dependent.
J/ Decays?
Awaiting CLEO-c
What about 2++ and 0?
The Scalar MesonsCrystal Barrel proton-antiproton annihilation
May 31, 2006 CIPANP 200636
What will we learn?
There is a clear signal for hybrid mesons – Exotic quantum numbers – but confirmation requires the observation ofa nonet, not just a single state.
Mapping out more than one exotic nonet is necessary toestablishing the hybrid nature of the states.
Decay patterns will be useful for the exotic QN states,and necessary for the non-exotic QN states.
May 31, 2006 CIPANP 200637
Summary
The first round of J/ experiments opened the doorto exotic spectroscopy, but the results were confused.LEAR at CERN opened the door to precision, high-statisticsspectroscopy experiments and significantly improved bothour understanding of the scalar mesons and the scalar glueball. Pion production experiments at BNL (E852) and VESopened the door to states with non-quark-anti-quarkquantum numbers.CERN central production (WA102) provided solid new dataon the scalar sector, and a deeper insight into the scalarglueball.
BES is collecting new J/ data. CLEO-c can hopefullyadd with the 0 program.
May 31, 2006 CIPANP 200638
The Future
The GlueX experiment will be able to do for hybridswhat 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 – PANDA.
May 31, 2006 CIPANP 200639
Significance of signal.
May 31, 2006 CIPANP 200640
Exotic Hybrid Results
1+- 1(1400)
1+- 1(1600)
1+- 1(2000)