Gluonic Excitations of

February 7, 2003 Curtis A. Meyer1

Gluonic Excitations of

Curtis A. MeyerCarnegie Mellon University February 7, 2003

Hadrons


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


QCD

u

d s

c

b

t

white

white

Six Flavors of quarks

is the theory of quarks and gluons

3 Colors3 Anti-colors

8 Gluons, each of which has a color an an anti-colorCharge.

)(21)(

GGtrmDiLQCD


Jets at High EnergyDirect evidence for gluons come from high energyjets. But this doesn’t tell us anything about the “static” properties of glue. We learn something abouts

q

q

2-Jet

q

q

g3-Jet

gluon bremsstrahlung gqqqq )()(


Deep Inelastic ScatteringAs the nucleon is probed to smaller and smaller x,the gluons become more and more important. Muchof the nucleon momentum and most of its spin is carried by gluons!

Glue is important to hadronic structure.


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”


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


Nonet Mixing

The I=0 members of a nonet can mix:

ssdduu 3

11

ssdduu 26

18

SU(3) 8

1

cos

sin

sin

cos

'

f

f

physicalstates

Ideal Mixing:

ss

dduu

f

f 2

1

'

3

1sin

3

2cos


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


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


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


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.


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)


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 &


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.


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


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


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


Higher mass glueballs?

Part of the CLEO-c program will be to search forglueballs 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 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.


Lattice QCD

Flux

tube

forms

between

qq

From G. Bali

Flux Tubes Realized

Confinement arises from flux tubes and their excitation leads to a new spectrum of mesons

Color Field: Because of self interaction, confining flux tubes form between static color charges


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+-

,,


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


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


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)


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


(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


Significance of signal.


p p

At 18 GeV/c

suggests p 0 p

p

to partial wave analysis

M( ) GeV / c2 M( ) GeV / c2

E852 Results


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


Exotic Signals1(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)

1 IG(JPC)=1-(1-+)

’1 IG(JPC)=0+(1-+)

1 IG(JPC)=0+(1-+)

K1 IG(JPC)= ½ (1-)

In a nonet, there should only be one 1 state.

Both of these are lighter than expectations, andThe decay modes are not what is expected.


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

__

__


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

1 b1 ,

’1

Couple to V.M + e

1-+ nonet

in Photoproduction


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


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


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


What will we learn?

There is an 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.


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.


The Future

CLEO-c will reopen the J/ studies with 100 timesExisting statistics. One goal is to find and study thePseudoscalar (0-+) and tensor glueball (2++)

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.

The CLAS experiment at Jefferson Lab is opening asmall window to meson spectroscopy in photoproduction.


Gluonic Excitations

Workshop at JLab May 14-16, 2003.

Documents

Gluonic Excitations of