in

Not the best time to be giving a perspective on QCD in the domain of spectroscopy

On second thought....

R L Jaffe JLab June 2004 Anxious times for friends of exotics... • SPRing - 8 I & II • Old phase shift analyses • CLAS I & II • CDF (uudds*, uuddc*, • Saphir uussd*) • Diana @ ITEP • HyperCP & E690 (FNL) • Compendium • E690(uuddc*) • Hermes • Zeus (uuddc*) • Zeus • HERA-B (ddssu*) • COSY-TOF • Aleph, Delphi, OPAL • NA49 (uussd*, ...) • STAR & Phenix • H1 (uuddc*) • FOCUS (uussd*) • BaBar (uudds*, uuddc*)

R L Jaffe JLab June 2004 QCD

• Deep Inelastic ★★★★ • Chiral dynamics ★★★ • Lattice (brute force) ★★★ • QGP (thermal equilibrium) ★★ • Spectroscopy ★ Relatively quiet for many years Now reawakening!

R L Jaffe JLab June 2004 Spectroscopy • Actually extraordinarily successful • Great breakthroughs occured before the advent of QCD! • Quarks are the effective degrees of freedom in QCD

confinement & quarksquarksquarks QUARKSQUARKSQUARKS chiral symmetry gluons gluons PIONS PIONS Remarkable!breaking

Short distances LongR L Jaffdistancese JLab June 2004 Models • Match naturally to DIS degrees of freedom • & -- spectroscopy & electroweak interactions • Never fully consistent with relativity -- relativistic single models but not field theoretic • Not the basis of a systematic expansion improving in accuracy

R L Jaffe JLab June 2004 Chiral Soliton Models • Non-strange, ground state baryons • Negative parity baryons via scattering theory. • Extension to s-quarks -- controversial at best • Relation to QCD? Motivated by large Nc but large Nc gives quark Hartree picture (Witten). Skyrme? One flavor? • No place for mesons or heavy quark hadrons! R L Jaffe JLab June 2004 Systematic large N expansions Jenkins, Manohar, Dashen • Somewhat systematic and apparently quite predictive • New flavor symmetries at large N • Relations without dynamics • No insight into mesons

R L Jaffe JLab June 2004 Personally... • Quark models got a bad rap in the past 20 years. • They’ve given us great insight into spectrocopy, and • They offer the best present hope of a comprehensive, reasonably predictive, and heuristic approach to the QCD spectrum. • But they have many theoretical problems! With these thoughts in mind... R L Jaffe JLab June 2004 DoesDoes thethe ϴϴ exist?exist? YES NO

Lots to do... A different agenda 10 questions for the Thoughts on immediate future spectroscopy

DIQUARK CORRELATIONS IN QCD

R L Jaffe JLab June 2004 Key to symbols... Programmatic ! implications for JLab

Theoretical difficulty raising questions about the Theta

R L Jaffe JLab June 2004 10 questions about exotics 1. What are the parity, width, spin, and ! isospin of the Theta? • Parity is crucial Positive causes problems: CSM, correlated quarks Negative causes more problems: Resonate? ! − !(KN) =0|Θ(1/2 )" = 1 • Width is bizarre: < 20 MeV, < 5 MeV, < 1 MeV, <.2 MeV ... Quantify unnaturalness: Λ (1520) D-wave width to KN is ~7MeV Jain & Jaffe (t.b.p.) • J = 1/2 or 3/2 or ...?

• I = 0 ! -- though even that is challenged! R L Jaffe JLab June 2004 2. What is the Theta production mechanism? !

− + • ϴ has been seen in γA → K (K p)X − γA → K (KSp)X " ep → e (KSp)X ZEUS + pp → Σ (KSp) νA → (KSp)X... • ϴ or its partners have not been seen at BaBar CDF, Hyper-CP, E-690 (at FNAL) H1(ϴ) & ZEUS (ϴc) HERA-B FOCUS ALEPH & DELPHI & OPAL(?) ... R L Jaffe JLab June 2004 3. Where are the exotic SU(3) partners of ! the ϴ? −− • Ξ (ddssu¯) + • Ξ (ssuud¯) • Must exist and must be relatively light in all sensible models -- despite early controversy

-- Ξ has been seen at NA49 But not confirmed! (in trouble)

R L Jaffe JLab June 2004 4. Where are the heavy quark partners of the ϴ?

• Strong arguments that light ϴ implies stable c- and b- analogues

• And even lighter negative parity states are allowed for c- and b- Stewart, Wessling & Wise

+ Θc has been seen at H1 But not confirmed by Zeus! (in trouble)

R L Jaffe JLab June 2004 5. Where are the cryptoexotic partners of the ϴ? ! + Θ • All schemes for the Θ for also predict non-exotic SU(3) partners N8 N1−0

• CSM → other members of Λ Σ 8 Σ1−0 antidecuplet

• Correlated quark models → antidecuplet and octet! − − − 0 + Ξ 3/2 Ξ3/2 Ξ3/2 Ξ 3/2 − 0 Ξ Ξ Candidate for Roper 1/2 1/2 and other extraneous baryons Octet and Antidecuplet Ambitious, important, and complex program!

R L Jaffe JLab June 2004 6. Are there other exotic baryon multiplets?

• CSM: teeming with exotics... 10* 27, 35, 28, ... • Uncorrelated quark models also predict many exotics, but typically non-resonant. • Correlated quark models Predict no further light, prominent exotics !

7. What are the relation to and implications for exotic and cryptoexotic qqq*q* mesons? • Quark models that predict the Θ typically predict exotic and cryptoexotic -- supernumerary -- mesons • The scalar saga! Amsler & Tornqvist P.R. (2004)

R L Jaffe JLab June 2004 8. Where are the spin-parity partners of the Θ?

• CSM -- 1/2+ only • Quark models invariably 1/2+ and 3/2+ nearby

9. What can electroweak interactions tell us about the Θ and friends? • γp → Θ γp → N(1440), N(1700), ... ! − • In principle νn → µ Θ

R L Jaffe JLab June 2004 10 What is the dynamical lesson for QCD in general (if the Θ exists)?

• Diquarks -- with or without exotic baryons -- an ! organizing principle for QCD spectroscopy (more later).

• CSM -- mixed messages Diakonov, Petrov, Polyakov Cohen; Itzhaki, Klebanov, Ouyang & Rastelli

R L Jaffe JLab June 2004 • Large Nc -- indications are strong that ! exotic baryons do not occur at dominant order in Nc as Nc → ∞. Manohar-Jenkins approach can derive useful relations among masses and couplings beyond leading order.

• Lattice QCD -- First wave of simulations now available: Sazaki; Csikor, Fodor, Katz, and Kovacs; (MIT/JLab lattice group):

Binding not established but negative parity Theta seems consistently to be lighter than positive parity!

R L Jaffe JLab June 2004 DoesDoes thethe ϴϴ exist?exist? YES NO

A different agenda Lots to do... Thoughts on baryon 10 questions for the spectroscopy immediate future

DIQUARK CORRELATIONS IN QCD

R L Jaffe JLab June 2004 Some facts about the spectrum....

• Resonances have been observed in every non-exotic baryon and meson channel • Despite years of effort, no resonance has ever been observed in any channel • Ditto for baryons, except for the θ! • One glaring extraneous multiplet among all hadrons: The light nonet of scalar mesons. • What dynamical principle can account for this qualitative systematics?

R L Jaffe JLab June 2004 Degrees of freedom in the spectrum • QUARKS ★★★ • PIONS ✓ • GLUONS ? • DIQUARKS ! • DIQUARKS ? The color, flavor, spin antisymmetric diquark is an important but underappreciated ingredient in QCD!

R L Jaffe JLab June 2004 And, lest we forget, where are the degrees of freedom in QCD spectroscopy? • are a hard slog • apparently not narrow • indistinct • supernumerary, but other non QQ* states. • Hybrids may be clearer • spin-parity exotics, eg. 1–+ • hybrid baryons, eg. L=1 [56] and Δ(5/2–)! • Λ(1405)?

( R L Jaffe JLab June 2004 Correlations in Quark Spectroscopy

★ Well known s L uR 1 1 0 ˜ f c s λj !σj QQ uL dL s ★ What about Q Q ? ˜ !σ R λi i dR ★ Channels: + − + − QcΓQ ⇒ 0 , 0 , 1 , 1

★ Mean field Flavor Color Spin A A A [q1, q2] survival: 3 ( ) 3 ( ) 0 ( ) 3 (A) 6 (S) 1 (S) 6 (S) 3 (A) 1 (S) {q1, q2} 6 (S) 0 (A)

R L Jaffe JLab June 2004 Diquarks “Bad” “Good” {qq} Symmetric 6 [qq] – Antisymmetric 3 VECTOR [ud] {dd} {ud} {uu} SCALAR I3 {sd} {su} ˜ λj !σj [ds] [su]

˜ λi !σi {ss} Flavor Color Spin ∆E ⇔ 3 (A) 3 (A) 0 (A) -8 [q1, q2] QQ 6 (S) 3 (A) 1 (S) 8/3 R L Jaffe JLab June 2004 Diquarks Long history in QCD, but never in the mainstream (D. Lichtenberg) • Certain regularities in spectroscopy • Absence of L = 2 [20] of SU(6) • Systematic analysis of baryon and meson resonances. More later -- A. Selem & F. Wilczek in preparation • Condensation in quark matter at high density • QQ condenses in flavor antisymmetric channel generating color-flavor locked superconductivity • ∆I = 1/2 rule in nonleptonic weak decays • dominance gives good description of non- perturbative effects. • Systematic study by Neubert, Stech & collaborators in late 1980’s. R L Jaffe JLab June 2004 Diquark regularities in DIS • Baryon parton distribution function regularities follow from QQ en 2 F2 (x, Q ) 1 cf. Close & Thomas lim ep 2 = Known since 1960’s x→1 F2 (x, Q ) 4 ∆d 1 ∆u Recent JLab results lim = − lim = 1 x→1 d 3 x→1 u nucl-ex/0308011

+ − • Regularities in fragmentation ratios in e e to hadrons

Fragmentation Suggests ratios measured dominance of at LEP (Delphi) -- favored diquark. Σ/Λ ! 1

R L Jaffe JLab June 2004 Characterizing diquarks • Formally define color antitriplet diquarks in the presence of an infinitely heavy spectator quark (or Polyakov line)

Flavor antisymmetric Spin zero [ud]AQ MA

Flavor antisymmetric Spin zero [us]AQ MA + ∆A Flavor symmetric Spin one [ud]S Q MS Flavor symmetric Spin one [us]S Q MS + ∆S • Awaiting lattice calculations, estimate from charm and strange systems: M M 1 M ∗ M M M[ −S −M A]|Q = !2 (ΣQM) +− M(ΣQ)" − (ΛQ) [ S A]]s = 2053MeV [ S A]]c = 212 MeV

• Similarly: [∆S − ∆A]s = 80 MeV

R L Jaffe JLab June 2004 Limits on diquarks from higher twist... A. Vainshteyn & RLJ (in progress) “But aren’t strong correlations in QCD ruled out by the absence of large twist-four corrections to DIS?”

“How pointlike can diquarks be?”

2 1 / Q corrections to DIS are known to be small, and limit non-perturbative scales in QCD beyond Λ These limits constrain diquarks because twist-four operators include ones sensitive to diquark correlations... R L Jaffe JLab June 2004 Leading twist Twist four -- diquark operator However: “Good” diquark is spinless and does not contribute at twist four ! S !ψγµψ ψγν ψ" − Traces Dimension-6, spin-2 ⇒ twist-4, but only if quarks are coupled to maximum spin.

R L Jaffe JLab June 2004 Diquarks in the Hadron Spectrum

3¯ 3¯ 0 QQ f c s ⇒QQ

QQ behaves like a bosonic antiquark in both color and flavor. [ud] [ds] [su] spin singlet , color antitriplet , flavor antitriplet which should dominate spectroscopy when it can form

R L Jaffe JLab June 2004 No Exotic Mesons RLJ 1977 2 2 In principle Q Q could include 10f 10f 27f

However 3¯f 3f QQ ⊗ QQ ⇒8f ⊕1f Compare 3f 3f q¯ ⊗ q ⇒8f ⊕1f

A nonet with JPC = 0++ For which there is good evidence!

R L Jaffe JLab June 2004 Scalar Nonet Scalar Meson _ _ Nonet [su] [ds] Hidden Strangeness _ _ [su][ud] [ud] _ [su][ds] [ud] _ } _ [ud][ud] [ds][ds] + _ [ds] [su] [su][su]

R L affe CERN March 2004 Summary of Scalar Meson Data – QQ -NONET KNOWN SCALAR MESONS s–s MASS

f (1500) – 1500 MeV 0 us a (1450) 0 κ(1430) – f 0 (1370) ud – uu–+dd –– a (980) QQQQ -NONET 1000 MeV 0 f 0 (980) – [su][d–s] κ(800) [su][–su–] –– + – [ud][ds] ( [sd][–sd])

f 0 (600) – – [ud][ud] 500 MeV

-1 0 1 Isospin

R L Jaffe JLab June 2004 Dibaryons Q6 • Short distance repulsion in NN [u,d] is a spinless . Consider deuteron: [ud][ud][ud], anti- symmetric in color! Requires overall antisymmetry in space: −−→ −−→ −−→ COALESCED[u, d] × ST[AuTE, d ]IS· [MUCHu, d] MORE MASSIVE THAN DEUTERON 3 • Only one s-wave Q Q state H-dibaryon [u, d][d, s][s, u] • However, these contain ! So LESSPauli blockingBOUND diminishes THAN NAIVEattraction. ESTIMA IndeedTES? naive (!) H is not pure

R L Jaffe JLab June 2004 Pentaquarks Q4Q

3f 3f 3f QQ ⊗ QQ ⊗ q¯ ⊃ 1f ⊕ 8f ⊕ 8f ⊕ 10f

1f ⊕ 8f Negative parity s-waves

8 ⊕ 10 2 f f Positive parity p-waves [ud] –s

– 2_ [ud][us]s [ud] d [su][ud]–s – – [su][ud]d [su][ud]d 2_ [su] s – 2– 2– [ds][su]d [ds] u – [su] d [ds][su]d

R L Jaffe JLab June 2004 Binding and prominence? • s-wave [u,d][d,s]u* etc. • Not exotic (1 + 8 ) • Odd parity • Very likely broad into open channels • p-wave [u,d][u,d]s* etc. • 8 + 10* • Narrow width from color/flavor/spin recoupling. • Pay the cost of orbital excitation in order to enjoy good diquark binding. • Predict overall mass scale?? • Other light quark exotic SU(3) representations are quite unlikely ---

R L Jaffe JLab June 2004 HIgher Exotics?

• Good-good [qq] ⊗ [qq] ⇒ ⊗ _ 6 3 Hea • Good-bad [qvyq] ⊗ {qq} ⇒ ⊗ ⇒ 10 ⊗ 27 ⊗ .... , broad, 1obscur5' 3 e {qq} {qq} ... 27 35 .... • Bad-bad ⊗ ⇒ ⊗ ⊗ _ ⇒ ⊗ ⊗ 15 15' 6 First occurance of odd parity antidecuplet ¯ ¯ 6f ⊗ 3f ⇒ 8f ⊕ 10f Only possible ¯ 3f ⊗ 3f ⇒ 8f ⊕ 1f prominent exotic

R L Jaffe JLab June 2004 Diquark consequences/predictions if a light prominent uudds* exists * • 8 + 10* -- cryptoexotics including Roper • Light exotic cascades in both 8 and 10* • Positive parity for [qq][qq]q* 10* • No other light, prominent exotics, esp 27 • Possible stable charm and bottom analogues: uuddc* and uuddb* • Spin 1/2 and 3/2 nearby for each p-wave. Discussed in detail elsewhere....

* Shared by many correlated quark pictures (Karliner, Lipkin; Nussinov and now many others) R L Jaffe JLab June 2004 Octet and Antidecuplet masses and assignments. Fit to candidates: N(1440) Roper; Θ (1530); Σ (1660). Rough Mass Estimates Nearest 50 MeV – V M + 3∆ + 2α Σs uusss 1950 e

M –

1850 M + 2∆ + 2α Ξ Ξ ssuud 3/2

S –

S M + 2∆ + α Νs uudss 1750 A

M – M + ∆ + α Λ Σ(1660)*uudsd 1650 M + ∆ Θ(1530) * uudd–s 1550 – M Ν(1440)* uuddd 1450

*input R L Jaffe JLab June 2004 A longer perspective...

Including • Ordinary mesons and baryons • Ground state and beyond • • Pentaquarks (if they exist)

R L Jaffe JLab June 2004 Ingredients in a diquark paradigm for spectroscopy F. Wilczek, A. Selem

1. quarks and diquarks RLJ 2. lying on linear Regge trajectories without prominent “daughters” 3. and with negligible L•S interactions.

• Distinct from conventional -- mean field -- in which radial excitations are prominent and multiquark states (eg. diquark - antidiquark) are not • Lots of spectroscopic tests in the meson, baryon, and tetraquark sectors. • Re-invigorated by considerations of exotic spectroscopy.

R L Jaffe JLab June 2004 Diquarks in non-exotic spectroscopy* • Vast data on baryon resonances can be ordered by diquark structrure: • Good diquarks are lighter than bad [u,d] ---- q {u,d} ---- q • Linear Regge trajectories N (good) ∆ N (bad) • No spin orbit forces • Small example: L=0 939 1/2+ 1232 3/2+ nonstrange baryons L=1 1520 3/2- ... 1675 5/2- • Left over states are candidates for qqqqq* L=2 1680 5/2+ 1950 7/2+ 1990 7/2+ 8 + 10* L=3 ... 2400 9/2- 2250 9/2- • Excess mesons fit into L=4 2220 9/2+ 2420 11/2+ ... Selem and Wilczek in preparation scalar nonet... L=5 2600 11/2- 2750 13/2- ... * Selem and Wilcek, a small L=6 2700 13/2+ 2950 15/2+ ... sample R L Jaffe JLab June 2004 Conclusions -- a theorist’s perspective

• The Θ ( 1 5 3 0 ) may or may not be real. • The (quark model) ideas in which I have most faith cannot fix the overall mass scale of the qqqqq* sector • They do not decisively favor stability for the Θ ( 1 5 3 0 ) because the favorable correlation (diquark) can only be realized in the p-wave -- at the cost of excitation energy. • Chiral soliton model? Take your choice: a. Itzaki et al & Cohen: cannot be trusted in exotic sector b. Diakonov et al: decisively predicts stable, narrow

R L Jaffe JLab June 2004 • If the ϴ is real... • Exotic and cryptoexotic light quark spectroscopy • Heavy quark exotic spectroscopy • A long, strong, and clear experimental program • Whether or not the ϴ survives • Spectroscopy has broadly re-emerged as an important challenge in QCD • Diquark correlations seem to play an important, indeed central, role in the QCD spectrum, with important consequences for both meson and baryon spectroscopy

R L Jaffe JLab June 2004