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Quarks in Hadrons Quarks in Hadrons 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) • Neutrino 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 gluons PIONS PIONS PIONS Remarkable!breaking Short distances LongR L Jaffdistancese JLab June 2004 Quark Models • Match naturally to DIS degrees of freedom • Mesons & Baryons -- spectroscopy & electroweak interactions • Never fully consistent with relativity -- relativistic single particle 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 baryon 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- pentaquarks 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) N N− partners 8!10 • 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 meson 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 exotic meson 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 hadron 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 gluon degrees of freedom in QCD spectroscopy? • Glueballs 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 ˜λ !σ VECTOR j j [ud] {dd} {ud} {uu} ˜ λi !σi SCALAR I3 {sd} {su} [ds] [su] {ss} 3 (A) 0 (A) Flavor Color Spin ∆E ⇔ 3 (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..
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