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)