Forefront Issues in Meson Spectroscopy

July 24, 2006 National Nuclear Physics Summer School1

Forefront Issues in Meson Spectroscopy

Curtis A. MeyerCarnegie Mellon University July 24, 2006


Outline of Talk

• Introduction• Meson Spectroscopy• Glueballs

• Expectations• Experimental Data• Interpretation

• Hybrid Mesons• Expectations• Experimental Data

• Summary and 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. Not necessarily true – coupling proportional todaughter mass can distort this.


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, 4f0(1370)

Crystal Barrel Results

Establishes the scalar nonetSolidified the f0(1370)

Discovery of the a0(1450)

Xpp Study decays of X


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.


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.


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

Lattice of about 1600

~(|1>-|G>)~(|8>-|G>)~(|1>+|G>)


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?

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. Evidence fromBES for an (1760)! .


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


Flux TubesFlux Tubes


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 0.10Bernard(04) 1.792§0.139In the charmonium sector:1-+ 4.39 0.080+- 4.61 0.11

Splitting = 0.20

1-+ 1.9§ 0.22+- 2.0§ 0.110+- 2.3§ 0.6

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) first lattice prediction ~400MeV


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


Controversy

In analysis of E852 ± data, so evidence of the 1(1400)

In CBAR data, the 0 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.


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


-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 ’


-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


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.


New Analysis

Dzierba et. al. PRD 73 (2006)

Add 2(1670)! (L=3)Add 2(1670)!3Add 2(1670)! ()SAdd a3 decaysAdd a4(2040)

10 times statistics ineach of two channels.

Get a better descriptionof the data via momentscomparison

No Evidence for the 1(1670)


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.


Exotics and QCDIn order to establish the existence of gluonic excitations,We need to establish the existence and 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


PhotoproductionPhotoproduction

More likely to find exotic hybrid mesons using beams of photons


The GlueX ExperimentThe GlueX Experiment


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+-


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


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. Recent analysis adds to controversy.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.


The Future

The GlueX experiment at JLab will be able to do for hybrids what Crystal Barrel and WA102 (together) did for glueballs. What are the properties of static glue in light-quark hadrons and how is this connected to confinement.

The antiproton facility at GSI (HESR) will look for hybrids in the charmonium system – PANDA. May also be able to shed more light on the Glueball spectrum.

Forefront Issues in Meson Spectroscopy

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