The Hunt for Glueballs, Hybridsand other QCD exotics

Ulrich WiednerUppsala University

XIV Nordic Meeting on Intermediateand High Energy Nuclear PhysicsGr‰ftÂvallen, Jan 4-10, 2002

The theory of strong interaction, QCD, has twoimportant ingredients:

1) asymptotic freedom perturbative QCD

2) confinement formation of hadrons

Ulrich Wiedner

QCD at short distances αS << 1

Quantitative description of the experimental cross section over 10 orders of magnitude by perturbative QCD

transverse jet energy

Perturbative QCD is extremely successful:

Jet production in pp-collisions at = 1.8 TeV s

Ulrich Wiedner

αS (Q2) → 1 for Q2 → 1 GeV2

10-18 10-17 10-16 10-15distance [m]

QCD at large distances

Ulrich Wiedner

The Experimental and Theoretical Challenge

Understand non-perturbative phenomena like:

confinement

chiral symmetry breaking

Ulrich Wiedner

masses

L=0

L=0

QCD

Baryon (qqq)

Glueball (gg)

Meson (qq)

Hybrid (qqg)

Ulrich Wiedner

Gluons exist:

Ulrich Wiedner

L

p

p

p

p

Meson Production("Gluon-rich" processes)

Radiative J/Ψ decays

Central Production

WA 79, WA 102

Doublepomeron

exchange?

J/Ψ

pp Annihilation

Mark III,DM2,BES

ASTERIX,Crystal Barrel,OBELIX

c

c

L

L

Ulrich Wiedner

π˚π˚π˚ Dalitz plot

f0(975) f0(1370)f0(1500)

f2(1565)

f2(1270)

m(π°1π°3)2 / [MeV/c2]2

m(π

° 1π°

2)2

/ [M

eV/c

2 ]2

700,000 events = 6 × 700,000 entries

pp 6γ

0

0

1

1

2

2

3 GeV2

3

mποπο2

mπο

πο2

712,000 eventspp → ποποπο (at rest)

f2(1565)

mηπο2

mηπ

ο2

0.6

0.6

0.8

1.0

1.2

1.4

1.6

0.8 1.0 1.2 1.4 1.6 GeV2

pp → ποηη (at rest)

m2(π0 KLmiss)

m2( π

0K

Lseen

)

0.4

0.6

0.8

1

1.2

1.4

1.8

2

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 GeV2

fo (1500)• K

LK

L

pp • πoKLK

L

37.500 events

1.2 1.3 1.4 1.5 1.6 1.7 GeV2

2.4

2.6

2.8

3.0

M2πη’

M2 ηη

’

f0(1500)

pp π°ηη'pp 5 π°

Phase

Spac

e

1000 1200 1400 1600

2000

4000

6000

CB Data

M4πο

Ulrich Wiedner

Decay properties

3

4

1

0

? ?

f0(1500)

K

ηη

π

π

ηη'

K

3

0.7 ± 0.3

0.8 ± 0.3

0.6 ± 0.3

L=0

π

π

ηη

K

K

Glueball

ηη'

Ulrich Wiedner

Ulrich Wiedner

Can this decay pattern be explained ?

Glueball-meson mixing

Interpretation difficult !

Help from theory ?

J. Sexton et al., Phys.Rev.Lett. 75, 4563 (1995):

C. Amsler, F. Close, Phys.Rev. D53, 295 (1996); F. Close, LEAP96:

G G

q

q

f0(1370) = -0.50 |G> + 0.13 |ss> + 0.86 |1/√2 (uu+dd)>

f0(1500) = 0.61 |G> - 0.61 |ss> + 0.43 |1/√2 (uu+dd)>

f0(1710) = 0.60 |G> - 0.76 |ss> + 0.22 |1/√2 (uu+dd)>

f0(1710) = 0.88 |G> + 0.33 |ss> + 0.34 |1/√2 (uu+dd)>

f0(1500) = -0.22 |G> + 0.91 |ss> – 0.36 |1/√2 (uu+dd)>

f0(1370) = -0.43 |G> + 0.25 |ss> + 0.87 |1/√2 (uu+dd)>

Ulrich Wiedner

Crystal Barrel sees a new isovector state:a0(1450): M = 1450 ± 40 MeV πη

Γ = 270 ± 40 MeV

The old possible nonet of scalar mesons:

A new possible nonet:

S

I3

a0(980)a0(980) a0(980)

K0(1430)K0(1430)

K0(1430)K0(1430)

0*

0*–*

+*

+–

f0(980) ?

S

I3

a0(1450)a0(1450) a0(1450)

K0(1430)K0(1430)

K0(1430)K0(1430)

0*

0*–*

+*

+–

? ?

Isoscalar 0++ resonances seen by Crystal Barrel

+ other experiments:

Too many resonances

f0(1450): M = 1446 ± 5 MeV 4πΓ = 56 ± 12 MeV

f0(1590): M = 1581 ± 10 MeV ηη' ηη 4πΓ = 180 ± 17 MeV

f0(1525): M = 1525 MeV ΚΚΓ = 90 MeV

fJ(1710): M = 1709 ± 5 MeV ΚΚ ππΓ = 140 ± 12 MeV

f0(975): M = 980 ± 20 MeV ππΓ = 100 ± 20 MeV

f0(1370): M = 1365 ± 50 MeV ππ ηη 4πΓ = 270 ± 80 MeV

f0(1500): M = 1511 ± 8 MeV ππ ηη ηη'Γ = 116 ± 17 MeV KK

Decay mode

Ulrich Wiedner

Ulrich Wiedner

Interpretation of the results:

f0(980), a0(980): KK-molecules

f0(1370): Nonet member

f0(1525), f0(1710): Nonet member

f0(1500) = f0(1590) = f0(1450): Exotic

Why is the f0(1500) an exotic?

Can we learn something from thedecay width ?

Quark models and other nonets:

287±14

MeV270±40

MeV

Γ (K*) < Γ (a0) < Γ ss) < Γ (nn)

Γ (f0(1500)) ηη, ηη ', KK ~ 15 MeV

Γ (f0(1500)) 4π, ππ ~ 100 MeV

Γ (f0(1500)) ππ ~ 20 - 30 MeV

no ss state

no nn state

The width of the f0(1500)Γ = 116±17 MeV

does not fit into the 0++ nonet

Ulrich Wiedner

Meson Productionin

γγ Collisions

... acts as an "Anti-Glueball Filter".

e+

e–

Coupling toelectric charges

Ulrich Wiedner

γγ Collisions from ALEPH

(Anti-Glueball Filter)

no f0(1500)

upper limit:Γ(γγ → f0(1500)) • BR(f0(1500) → π+π−) < 0.31 keV

Phys. Lett. B472 (2000) 189.

Ulrich Wiedner

Glueball – meson mixing occurs when both decayinto the same final states.

The light scalar (0++) glueball can decay solelyinto pseudoscalar mesons and ρρ, just like anyother light quark meson.

mixing unavoidable

Solution:

Understand the complete light-quark mesonspectrum experimentally and theoretically.

Ulrich Wiedner

N 2S+1LJ

1 1S0

1 3S1

1 1P1

1 3P0

1 3P1

1 3P2

1 1D2

1 3D1

1 3D2

1 3D3

1 3F4

2 1S0

2 3S1

2 3P2

3 1S0

JPC

0–+

1––

1+–

0++

1++

2++

2–+

1––

2––

3––

4++

0–+

1––

2++

0–+

I = 1

π

ρ

b1(1235)

a0(1450)∗

a1(1260)

a2(1320)

π2(1670)

ρ(1700)

ρ3(1690)

a4(2040)

π(1300)

ρ(1450)

π(1800)

I = 0

η, ηη'

ω, φφ

h1(1170), h1(1380)

f0(1370)∗ , f0(1710)∗

f1(1285), f1(1420)

f2(1270), f2'(1525)

η2(1645), η2(1870)

ω(1650)

ω3(1670), φφ3(1850)

f4(2050), f4(2220)

η(1295), ηη(1440)

ω(1420), φφ(1680)

f2(1810), f2(2010)

η(1760)

I = 1/2

K

K*(892)

K1B†

K0*(1430)

K1A†

K2*(1430)

K2(1770)

K*(1680)‡

K2(1820)

K3* (1780)

K4*(2045)

K(1460)

K*(1410)‡

K2* (1980)

K(1830)

ud, uu, dd uu, dd, ss su, sd

Review of Particle Physics 2000

contributions from LEAR experiments

Ulrich Wiedner

Higher mass glueballs (e.g. 2++) can have decaymodes that are OZI suppressed for (u and d) mesonslike φφ or φη.

The observation of such decay modes makes astrong case for a glueball appearance.

Glueballs with exotic quantum numbers do notmix with mesons and should be narrow (bumphunting).

Lattice based calculations:

NO light mesons may exist > 3.2 GeV(string breaking and color screaning)

M. Brisodova et al., Phys. Lett. B460, 1 (1999)M. Brisudova et al., Phys. Rev. D61, 054013 (200)

Higher-mass Glueballs

ANY glueball could be narrow if MG > 3.2 GeVand

ANY signal (besides cc states) could be a glueballor exotic

Ulrich Wiedner

C. Morningstar, M. Peardon; Phys. Rev. D 60 (1999) 034509

Charmonium

4000

2000

0++2++ 1+– 2-+ 3++ 1++ 1-- 3--

0-+ 0+- 1-+ 2+- 2-- 0-- 3-+3+-

JPC

UKQCD Collaboration, G. S. Bali et al., Phys. Lett. B309 (1993) 378.

6000

[MeV]

Ulrich Wiedner

Charmonium States and PredictedGlueballs

0.5 1.0 1.5 2.0 2.5 3.0

0.5

1.0

1.5

2.0

2.5

3.0

1

10

100

a2(1320)

a2(1320)

ρ–(770)

ρ(1400)

52,576 events

m2 (η

π−)

[G

eV/c

2 ]2

m2(ηπ−) [GeV/c2]2

pd π–π η + pspectator

(<100 MeV/c)

Ulrich Wiedner

Decay: (ηπ)L=1

Mass: 1400 ± 30 MeV

Width: 310 ± 70 MeV

Quantum Numbers: JPC = 1–+ (I =1)

not possible from qq

Properties of the ρ(1400)

Previous indications of this resonance:

P = (–)L+1

C = (–)L+S

J = L + S

π–p (π η)n (GAMS/CERN, 100 GeV/c, 1988)π–p (π η)n (VES/Serpukhov, 100 GeV/c, 1993)π–p (π η)n (E852/Brookhaven, 18 GeV/c, 1997)

M: 1300 – 1400 MeV, G: 150 – 400 MeV

Ulrich Wiedner

• Complicated analysis (x 10 more amplitudes for high L-waves, exchange)• Dominant a2(1320); feedthrough to P+ wave, background (few percent) • Phase motion relative to a2(1320) indication of resonance

D+

P+

1.0

5000

10000

15000

1.2 1.4 1.6 GeV

1.0 1.2 1.4 1.6 1.8

Eve

nts

/ 0

.04

Ge

V

a2(1320)

ρ(1320)

Ph

ase

Diff

ere

nce

[ra

d]

∆φ (D

+ -

P+)

0.5

0.

1.0

1.5

exotic wave

mηπ

Phase [rad]

vs. production in 18 GeV/c π− beam (BNL-E852)

Hybrid production in pp annihilation

Ulrich Wiedner

1 32 GeV2

a2(1320)

ρ(1400)

A second exotic particle (JPC=1–+)

Crystal Barrel:

pp π+π–η'

π1(1600): M = 1563 ± 30 MeV/c2Γ = 195 ± 50 MeV/c2

preliminary, LEAP2000 conference

BNL (E852):

π–p ρπ–p

π1(1600): M = 1593 ± 8 MeV/c2Γ = 168 ± 20 MeV/c2

Phys. Rev. Lett. 81 (1998) 5760

Ulrich Wiedner

preliminary, Joerg Reinhardt, Bonn

()S a2(1320) a0(1450) 1 lnL

(1585,160)

22.72 77.28 - - - 164.2

18.68 80.78 0.53 - - 158.31

33.75 40.35 0.01 25.9 - 134.1

24.26 64.0 1.23 2.39 8.04 126.63

22.72 77.28 - - - 164.2

18.68 80.78 0.53 - - 158.31

27.15 64.7 1.33 - 6.82 127.83

24.26 64.0 1.23 2.39 8.04 126.63

(1567.7,158.2)

26.93 64.5 1.28 - 7.08 127.28

(1563,195.0)

23.64 61.3 1.24 3.76 10.1 125.86

Fit of Dalitz plot

Ulrich Wiedner

Two-BodyThresholds

ΣcΣc

ΛcΛc

ΩsΩs

ΞsΞs

DD

ΣsΣs

ΛsΛs

ΞcΞc

LEAR

p M

omen

tum

[GeV

/c]

ΩcΩc

Mesons and Exotics

6

3

4

2

1

5

Light Mesonsπ,η,ω,φ,ρ,f,a,h,K

Charmed MesonsD, Ds

CharmoniumJ/Ψ, χ, Ψ(2S)

Bottom MesonsB, Bs

ssgddguug

ccgccqq

qqqq

Predicted "Exotics"qq Mesons

Mas

s [G

eV/c2

]

ggggg

at rest

2

4

6

8

10

12

1415

Ulrich Wiedner

DissociationEnergy

23S1

11S0

21P1

21S0

13S1

23P1

23S1 23P2

23P0

n = 1

n = 2

Rel

ativ

e E

nerg

y (e

V)

Positronium

7

6

5

4

3

2

1

0

L = 0Singlet Triplet

L = 1Singlet Triplet

Charmonium

23S1 ψ'

23P1 χ1

23P2 χ221P1 hc

21S0 η'c

11S0 ηc

13S1 ψ

Rel

ativ

e E

nerg

y (M

eV)

Qua

si-b

ound

sta

tes

Bou

nd s

tate

s

DD threshold

23P0 χ0

L = 0Singlet Triplet

L = 1Singlet Triplet

1000

900

800

700

600

500

400

300

200

100

0

–100

Ulrich Wiedner

Ulrich Wiedner

ηc'

ηc

χ2

χ1 χ0

χ0,1,2 γJ/ψ

Charmonium Spectrum

Ulrich Wiedner

Singlet Triplet Singlet Triplet Singlet Triplet

3.0

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

Mas

s [G

eV]

L = 0 L = 1 L = 2

ηc

χ1

J/ψ

ηc'

ψ'

χ0

χ2hc

1D23D2

DD threshold

0–+

0–+

1--

1--

1+– 2++

1++

0++

2–+ 2--

(13.2)

(0.09)

(13.5)

(0.88)(<1.1)

(<8)

(0.27)

(2.0)

Charmonium spectrum ...

... "clean" and understood.

Identification of additional states easier than inthe light meson sector.

e+

e–

e+

e–

JPC = 1–– J = 0, 2C = +

p

p

p

p

J = 0, 2, ... J = 1C = + C = –

Meson production: e+e– vs. pp

2-γ experiments difficult, since it is mostly1-γ annihilation restricted q.n. (1––).

All quantum numbers possible all mesons can be produced directly.

Ulrich Wiedner

Production:Crystal Ball

γ e+e–

γ J/ψ

pp χ1,2

Formation:

σm (beam) = 0.5 MeV

E 760 (Fermilab)

γ γ e+e–

γ γ J/ψ

e+e– ψ'

γ χ1,2

Ulrich Wiedner

Decay of charmed hybrids

c

cg

µ+

µ−

cc

Decay of charm into leptons provides a clean "tag".

Charmonium

Charmed Hybrid

η

Ulrich Wiedner

Glueball Production in ccg Decays

Charmed Hybrid

Charmed Hybrid

Charmonium

Glueball

Glueball

Glueball

Ulrich Wiedner

Cascade decay

C = +

Same C parity µ+

µ−

Decay by annihilation

C = –(suppressed by αs)

Indications for a J/ψφ resonances?

BABAR can expect ~300 events within 5 years.

M2 (J

/)(

GeV

2 /c4 )

M2( K)(GeV2/c4)

2031099-00424.0

2.016.0

17.0

18.0

19.0

20.0

21.0

22.0

23.0

5.04.54.03.53.02.5

4.35 GeV/c24.5 GeV/c2

New Results from CLEO

Phys. Rev. Lett. 84, 1393 (2000)

B J/ψφK

4.7 GeV/c2

Ulrich Wiedner

The new GSI Accelerator Complex

Par

alle

l Ope

rati

on o

f B

eam

s

e – cooling

HE

SR

Mom

entum Spread:

δp/p ≥ 7×10

–6

Max. L

uminosity:

2×10

32 cm–2 s

–1

Max. M

agnetic Rigidity:

50 Tm

( ⇔ 15 G

eV/c p )

Circulating p: ≤ 2×

1012

Beam

radius at target:0.03 m

m

Ulrich W

iedner

Universal Detector

Detector features:tracking of charged particles measurement and identification of γ, e±, µ±, π±, K±, p, p high rate capability sophisticated and fast trigger scheme

Ulrich Wiedner

JPCFermion-Antifermion

Ulrich Wiedner

How to make resonances?

Produktion experiments:

Formation experiments:

all quantum numbers possible

identical quantum numbers

P = (–)L+1

C = (–)L+S

J = L + S

Signal in production but no signal in formation

Production vs. Formation

Formation experiments cannot produce exotic JPC.

Production experiments can produce exotic JPC.

A detector should be suited for both:

production and formation

very interesting

Ulrich Wiedner

The HESR is not only a unique facility, it is theonly one that allows to study:

Hybrids in e+e–:

Glueballs, Hybrids, Hadrons

Lattice:WEAK direct production even of 1–– states,since wavefunction at the origin is small.

B-decays lack statistics.

Central production in pp collisions:

Difficult to see even normal charmonium states.

C. Michael, Nucl. Physt. A655, 12c (1999)

Ulrich Wiedner

* For selected decay mode

** L = 2×1032 cm–2s–1, 50 % detection and accelerator efficency Integrated luminosity = 4 pb–1/ day

*** 1% B.R. for this decay mode

Charmonium Production in pp

cc JPC M [MeV]Γtot

[MeV]Decay mode

σ(M)* [pb]

Events/day**

ηc 0–+ 2980 13.2 γγ 550 4400

ηc 0–+ 2980 13.2 φφ 3100 24800

ηc' ??? 0–+ 3594 γγ 120 960

J/ψ 1–– 3097 0.087 e+e–/µ+µ– 630000 5040000

ψ' 1–– 3686 0.277 e+e–/µ+µ– 4480 35840

ψ' 1–– 3686 0.277 J/ψ X 17600 140800

χc0 0++ 3415 14 γγ 30 240

χc0 0++ 3415 14 γ J/ψ 52 416

χc1 1++ 3511 0.88 γ J/ψ 3600 28800

χc2 2++ 3556 2.0 γ J/ψ 3700 29600

χc2 2++ 3556 2.0 γγ 220 1760

ccg 1–– (4100) (0.2) (J/ψη***) (120) (960)

ccg 1–+ (4000) ??? (J/ψ ω,φ,γ) (9) (75)

Ulrich Wiedner

D mesons interactwith rest nucleus

pA ψ + (A–1)

D

p3.5 – 4.5 GeV

ψ (cc) decays into DD

D

p – Nucleus Interaction

Ulrich Wiedner

ψ(3770)

ψ(3770)

ψ(4160)

D–= dc

D+= dc

D0= uc

D0= uc–Ds = sc

+Ds = sc

quark – nucleusinteraction

=d (or d) – nucleus

interaction*

quark – nucleusinteraction

=u (or u) – nucleus

interaction*

quark – nucleusinteraction

=s (or s) – nucleus

interaction*

* ignoring c (or c) – nucleus interaction

Ulrich Wiedner

• rate at different nuclear targets

• angular distributions

• comparison to hydrogen

Experimental techniques:

• wire targets (like in HERAb)

• pellet targets (like in WASA-CELSIUS)

• D – triggers

Ds can be distinguished from D by theirdistinct decay into φ + anything (18 %).

± ±

Measurements:

Ulrich Wiedner

Topics not mentioned

Baryon Pair Production:

charmed: study threshold production for understanding ofc production mechanism

strange: ΩΩ produced via triple kaon exchange?comparison of production rates: ΩΩ vs. φφφ

CP Violation

Charm Physics in Nuclei:

J/Ψ - N cross section: color transparency?

exotic states of nuclear matter?

charmonium nucleus bound states?

mass shift of charmonium states in nuclear matter:( charmonium states are narrow below DD threshold!)

Ulrich Wiedner

Summary

The first QCD exotics have been found in highstatistics and high precision 4π experiments.

Other glueballs and hybrids must exist.

Studying the charmonium energy rangesimplifies life (small, well known states).

Many issues in normal charmonium spectroscopyare still unsettled.

Charmed hybrids (< 4.3 GeV) show up asadditional small states.

A dedicated accelerator with excellent beamproperties designed together with a highstatistics, high precision experiment is aworld class facility for hadron physics.

Their production rate is comparable to those ofnormal mesons in pp annihilations.

Ulrich Wiedner

E760/E835 has prooven how well suited pp isfor precision spectroscopy.