Hadron Spectroscopy: Results and Ideas.

Transcription

1 Hadron Spectroscopy: Results and Ideas. E. Klempt SFB/TR16 Helmholtz-Institut für Strahlen und Kernphysik Universität Bonn Nußallee 14-16, D Bonn, GERMANY International Workshop on NEW PARTIAL WAVE ANALYSIS TOOLS FOR NEXT GENERATION HADRON SPECTROSCOPY EXPERIMENTS June -, 1 Camogli, Italy

2 Hadron Spectroscopy: results and ideas 1. Why baryon spectroscopy. New results and PDG related issues 3. Baryon resonance spectrum: interpretation Parity doublets and chiral symmetry AdS/QCD SU(6) O(3) Dynamically generated resonances versus C.D.D. poles 4. New results from ELSA 5. Summary

3 1. Why Baryon Spectroscopy? Mass of the Universe: Dark energy 73% Dark matter 3% Intergalactic gas 3.6% } atoms Stars.4% Mass of atoms Mass of quarks 1% Mass of electrons.1% Field energy 99% What are these objects?

4 What are constituent quarks? Mass is field energy! M N =< N 9α s 4π (B E ) + flavors m i ψi ψ i N >. How to explore constituent quarks? xf Nucleon tomography: H1 and ZEUS Combined PDF Fit xg (.5) xs (.5) -3 1 HERAPDF.1 (prel.) exp. uncert. model uncert. - 1 Q = 1 GeV xu v xd v HERA Structure Functions Working Group April Goal: Distribution of linear and angular momenta of gluons and quarks in space Collectivity is lost! x σ tot Nucleon spectroscopy: [µb] E γ [GeV] W [GeV] M. Fuchs et al. (CB-ELSA collab.) in preparation Wave length matches the size of constituents Explores collective response!

5 Questions: - Are constituent quarks the relevant degrees of freedom? - What are the effective forces between them? Findings: - Linear Regge trajectories - Many more resonances expected in symmetric quark models than observed 3 Diquark substructure? QCD strings? AdS/QCD? H. Forkel and E. Klempt, Phys. Lett. B 679, 77 (9). Mass [MeV] J π L T J 1 **** * S ** 19 ** ** *** **** **** 144 **** 939 ****?? proton? 7 ** 9 8 * ** S S *** **** **** **** ** 19 **** 1675 **** 6 *** 5 **** 1/+ 3/+ 5/+ 7/+ 9/+ 11/+ 13/+ 1/ 3/ 5/ 7/ 9/ 11/ 13/ P11 P13 F15 F17 H19 H1 11 K1 13 S11 D13 D15 G17 G19 I1 11 I1 13? Non-strange N -resonances U. Löring, B. Metsch, H. Petry, Eur. Phys. J. A 1, 395 (1). Constituent quarks confinement potential + residual interaction wrong degrees of freedom?

6 Excited baryons from Lattice QCD MeV 31 R.Edwards et al., arxiv: [hep ph] (13) N(938) m = 4 MeV π 13 Exhibits the features SU(6) O(3)-symmetry (m π =4 MeV) Counting of levels consistent with non-rel. quark model Striking similarity with quark model No parity doubling The lattice seems not to solve the problems!

7 Hadron Spectroscopy: results and ideas 1. Why baryon spectroscopy. New results and PDG related issues 3. Baryon resonance spectrum: interpretation Parity doublets and chiral symmetry AdS/QCD SU(6) O(3) Dynamically generated resonances versus C.D.D. poles 4. New results from ELSA 5. Summary

8 . New results and PDG related issues J. Beringer et al. (Particle Data Group), Phys. Rev. D86, 11 (1). Resonance Rating N pp Resonance Rating N pp Resonance Rating N pp N(144)1/ + **** 13 N(15)3/ **** 17 N(1535)1/ **** 15 N(165)1/ **** 18 N(1675)5/ **** 14 N(168)5/ + **** 17 N(1685) * N(17)3/ *** 15 N(171)1/ + *** 14 N(17)3/ + **** 17 N(186)5/ + ** 9 N(1875)3/ *** 16 N(188)1/ + ** N(1895)1/ ** 17 N(19)3/ + *** 18 N(199)7/ + ** 9 N()5/ + ** 11 N(4)3/ + * N(6)5/ ** 13 N(1)1/ + * N(15)3/ ** 11 N(19)7/ **** 11 N()7/ **** 7 N(5)9/ **** N(6)11/ *** N(7)13/ + ** (13) **** 8 (16)3/ + *** 1 (16)1/ **** 1 (17)3/ **** 11 (175)1/ + * (19)1/ ** 13 (195)5/ + **** 11 (191)1/ + **** 13 (19)3/ + *** 1 (193)5/ *** (194)3/ * 5 (195)7/ + **** 13 ()5/ + ** (15)1/ * ()7/ * (3)9/ + ** (35)3/ * (39)7/ + * (4)11/ + **** (4)9/ **** (75)13/ ** (95)15/ + ** E.g.: V. Kuznetsov et al., Phys. Lett. B 647, 3 (7); V. Kuznetsov et al., Phys. Rev. C 83, 1 (11); I. Jaegle et al., Eur. Phys. J. A 47, 89 (11). M. Ablikim et al. [BES Collaboration], Phys. Rev. D 8, 54 (9). A. V. Anisovich, R. Beck, E. Klempt, V. A. Nikonov, A. V. Sarantsev and U. Thoma, Eur. Phys. J. A 48, 15 (1); N pp particle properties were determined; 4 in total. Be cautious, there are ambiguities! Promoted to three-star resonance

9 PDG related issues 1. Naming scheme: ++ (4): Need to know quantum numbers by heart ++ (4)H 3,11 : Refers to π + p scattering. Need to know that H corresponds to L = 5. Not straightforward to calculate N ω partial wave (which is also L = 5). ++ (4)11/ + is self explanatory and used in the new PDG edition.. Baryon part in PDG emphasizes properties of poles rather than of Breit-Wigner parameters 3. Branching ratios often not defined

10 γp pπ and γp pπ 14 1 Cascades via (13), N(15)3/, N(168)5/ + σ tot, µb CB-TAPS TAPS GRAAL CB-ELSA pπ / 3 Peak position change, pole positions remain M(γp), GeV/c ) 4 /c ) (GeV (pπ M ) 4 /c ) (GeV (pπ M ) 4 /c ) (GeV (pπ M M (pπ ) (GeV /c ) 4 M (pπ ) (GeV /c ) 4 M (pπ ) (GeV /c )

11 Three definitions of branching ratios: 1. BR a = Γ a /Γ BW, m BW Γ a = g a ρ a(m BW ), where the energy dependent partial is defined by s Γa (s) = g a ρ a(s), g a coupling constant, ρ a phase space. BRa = 1 satisfied.. BR = threshold ds π ga ρ(s) (m BW s) +(. ga ρ a(s)) a This definition allows for subthreshold decays. It corresponds to intuition but BR a 3. BR pole (channel b) = = 1 needs to be imposed. Res(πN b) Res(πN Nπ) (Γ pole /). The latter definition uses only pole related quantities.

12 Hadron Spectroscopy: results and ideas 1. Why baryon spectroscopy. New results and PDG related issues 3. Baryon resonance spectrum: interpretation Parity doublets and chiral symmetry AdS/QCD SU(6) O(3) Dynamically generated resonances versus C.D.D. poles 4. New results from ELSA 5. Summary

13 3. Baryon resonance spectrum: interpretation 3.1 Parity doublets and chiral symmetry In the limit of massless quarks: 1. Pseudoscalar mesons become massless Goldstone bosons. Parity partners acquire the same mass 3. Spontaneous symmetry breaking leads to hadronic masses Vector mesons Nucleon mass M N Its parity partner N(1535)1/ acquires a mass 7 MeV 1 MeV 15 MeV N(165)1/ N(17)3/ N(1675)5/ ()7/ a.o. N(171)1/ + N(17)3/ + N(168)5/ + (195)7/ + N(1895)1/ N(188)3/ N(6)5/ N(18)7/ N(187)1/ + N(189)3/ + N(9)5/ + N(15)7/ + Nucleon resonances organized as parity doublets (solution BnGa11-). Restoration of chiral symmetry? L. Y. Glozman, Phys. Rept. 444, 1 (7) Meson and baryon resonances on the leading Regge trajectory have no parity partner!

14 3. AdS/QCD M (GeV ) 3/ +(13) N= 1/ (16) 3/ (17) 3/ +(16) 1/ +(191) 3/ +(19) 5/ +(195) 7/ +(195) 1/ (19) 3/ (194) 5/ (193) 5/ (3) 7/ () 1/ + 3/ + 5/ +() 7/ + 5/ + 7/ +(39) 9/ +(3) 11/ +(4) 3/ 5/ (35) 7/ 9/ (4) / 11/ 5/ + 7/ + 9/ + 11/ + 9/ + 11/ + 13/ + 15/ +(95) 11/ 13/ (75) N=1 7/ 9/ L+N Regge trajectory of resonances: M L + N: non-relativistic concept! Mass is stored in strings which expand L + N (l 1, l ), (n 1, n ) = (L, N) Constituent quark mass is ill-defined AdS/QCD: H. Forkel and E. Klempt, Phys. Lett. B 679, 77 (9). M = a (L +N+3/) b α D Two-parameter fit reproduces mass spectrum better than quark models, Skyrme models (or LQCD)!

15 3.3 SU(6) O(3) J P = (56, + ) S = 3/; L = ; N= 1/ +(191) 3/ +(19) 5/ +(195) 7/ +(195) S = 1/; L = ; N= N 3/ + (17) N 5/ +(16) (7, + ) S = 1/; L = ; N= 3/ + 5/ + S = 3/; L = ; N= N 1/ + (188) N 3/ +(19) N 5/ +() N 7/ +(199) S = 1/; L = ; N= N 3/ + N 5/ + nd (, 1 + ) S = 1/; L = 1; N= N 1/ + N 3/ + (56, + ) S = 3/; L = ; N=1 3/ +(16) S = 1/; L = ; N=1 N 1/ + (144) (7, + ) S = 1/; L = ; N=1 1/ +(175) does not exist S = 3/; L = ; N=1 N 3/ + S = 1/; L = ; N=1 N 1/ + (171) 4th shell (7, 1 1 ) S = 1/; L = 1; N= 1/ (16) 3/ (17) 1 st S = 3/; L = 1; N= N 1/ (165) N 3/ (17) N 5/ (1675) S = 1/; L = 1; N= N 1/ (1535) N 3/ (15) th (56, + ) S = 3/; L = ; N= 3/ +(13) S = 1/; L = ; N= N 1/ + (939) Some multiplets are fully, others completely empty. Why?

16 There is a spin-doublet N 1/ (188), N 3/ (189). There is no close-by N 5/ There is no close-by spin triplet. There is 1/ (19), 3/ (194), 5/ (193) SU(6): 56 = A symmetric spin-flavor wave function with L = 1 excludes N =. These resonances are radial excitations belonging to the third shell There are for negative-parity resonances N 3/ (13), N 5/ (75), N 7/ (185), N 9/ (5). These may form a spin quartet There is no evidence for a (N 3/, N 5/ ) doublet There is a 7/ (); likely, 5/ is missing (GWU: 3 MeV). SU(6): 7 = These resonances can be assigned to the third shell L = 3

17 3 rd J P = (56,1 3 ) S = 3/;L = 1; N=1 1/ (19) 3/ (194) 5/ (193) S = 1/;L = 1; N=1 N 1/ (188) N 3/ (187) (7,3 3 ) S = 1/;L = 3; N= 5/ (3) 7/ () S = 3/;L = 3; N= N 3/ (17) N5/ (7) N 7/ (19) N 9/ (5) S = 1/;L = 3; N= (56,3 3 ), (,3 3 ), (7, 3 ), (7,1 3 ), (7,1 3 ), (,1 3 ) : Many states predicted, no candidates known There are two multiplets completely filled, six multiplets completely empty. Why? Minimal and maximal moments of inertia? Consequence of string dynamics?

18 3.4 dynamically generated resonances versus C.D.D. poles σ; Λ(145); ρ; (13); Meson-meson interactions: Meson resonances can be interpreted as Meson-baryon interactions: q q q qq q q qg gg m 1 m mesons tetraquarks hybrids glueballs molecules Baryon resonances can be interpreted as qqq qqqq q qqqg b 1 m baryons pentaquarks hybrids molecules Are all these Fock components realized and mix? Even the quark model predicts too many baryon states!

19 Two examples: The quark model predict five negativeparity N resonances N(1535)1/ can be generated dy- ] [GeV M 6 π (36) namically from N η ΣK interactions 4 π (7) [a] M - 1/ (16) 3/ - (17) - N 1/ (165) - N 3/ (17) - N 5/ (1675) π (18) 1 π (13) (13) - N 1/ (15) - N 3/ (1535) π (14) n q q meson resonances fall onto Regge trajectories q qg hybrids are predicted

20 A third example: scalar mesons Jaffe: Four quarks in S-wave, pairs of quarks in color 3 (antiquarks in 3), energetically favored over q q with orbital excitation. d suū S u sd d f, a = n ns s, 98 MeV dūs s 1 (uū + d d)s s u ddū 1 u ds s (uū d d)s s I 3 κ = n sn n, σ = n nn n, 67 MeV 46 MeV sūd d s duū 9 q q, 9 q qq q states SU(4)

21 Including c quarks: There are 36 tetraquark states with quark pairs in color 3, 16 of them have a q q component, are flavor exotics. There is a subset of 1 tetraquark states with open charm having a symmetry where the two quarks can form a 3 and two antiquarks a 3, 6 of them have a q q component. 4 of them are flavor exotics. c d uū ; c d s s ; c d d s ; c d sū ; c d u s cū d d ; cū s s ; cū u s ; cū s d ; cū d s D (4) = c n(uū + d d + s s)/ 3; D s (317) Flavor exotics have never been observed. So even if the dominant configuration has a four-quark nature, the q q component is essential to form a bound or resonant state! Conclusion: The Fock expansion is realized in the form ψ(q) > = α 1 qqq(q) > + α qqqq q(q) > + α 3 qqqg(q) > + α 4 b 1 m (Q) > and there are no additional states beyond the quark model (perhaps exotics, perhaps chemistry of heavy-light systems) This does not exclude that mesons like a (98) have a large or even dominant K K configuration but the raison d etre is their q q component.

22 Hadron Spectroscopy: results and ideas 1. Why baryon spectroscopy. New results and PDG related issues 3. Baryon resonance spectrum: interpretation Parity doublets and chiral symmetry AdS/QCD SU(6) O(3) Dynamically generated resonances versus C.D.D. poles 4. New results from ELSA 5. Summary

23 3. New Results from ELSA ELSA A step forward towards a complete experiment

24 CBELSA/TAPS: Double pol. exp. γ p pπ (A. Thiel, Bonn) Linearly polarized photons, longitudinally polarized target ( ) dσ dσ (Φ) = dω dω 1 P lin γ Σ cos(φ) + Plin γ P zgsin(φ) Target 45 Target φ Target + 45 Target φ γ p pπ (E γ =75-1 MeV) Clear effect from G observed φ φ

25 CBELSA/TAPS: Double pol. exp. γ p pπ (A. Thiel, Bonn) Linearly polarized photons, longitudinally polarized target: G dσ dσ (Φ) = (1 P dω dω lin γ Σ cos(φ) + P lin γ P z G sin(φ) ) already in the second resonance region: significant differences! related to the E +, E -multipoles 1/, 3/ -partial waves MAID BnGa SAID

26 CBELSA/TAPS: Double pol. exp. γ p pπ (M.Gottschall) Circularly polarized photons, longitudinally polarized target: E MAID BnGa SAID

27 CBELSA/TAPS: Double pol. exp. γ p pη (J. Müller, Bonn) Circularly polarized photons, longitudinally polarized target: E Pol.Observable E preliminary Pol.Observable E preliminary E = 1-1 MeV meson cos θ E = 1-14 MeV meson cos θ MAID BnGa SAID

28 T CBELSA/TAPS: Double pol. exp. γ p pπ (J. Hartmann) Linear photon polarization, transversally polarized target: T MeV < E γ < 675 MeV 675 MeV < E γ < 75 MeV 75 MeV < E γ < 775 MeV 775 MeV < E γ < 85 MeV MeV < E γ < 875 MeV 875 MeV < E γ < 95 MeV 95 MeV < E γ < 975 MeV 975 MeV < E γ < 15 MeV MeV < E γ < 175 MeV 175 MeV < E γ < 115 MeV 115 MeV < E γ < 1175 MeV 1175 MeV < E γ < 15 MeV MeV < E γ < 175 MeV 175 MeV < E γ < 135 MeV 135 MeV < E γ < 1375 MeV 1375 MeV < E γ < 145 MeV preliminary cosθ π our data Booth et al. (1977) Maid Said BnGa

29 Measurement of the recoil polarization: P P.5 65 MeV < E γ < 675 MeV 675 MeV < E γ < 7 MeV 7 MeV < E γ < 75 MeV 75 MeV < E γ < 75 MeV MeV < E γ < 775 MeV 775 MeV < E γ < 8 MeV 8 MeV < E γ < 85 MeV 85 MeV < E γ < 85 MeV MeV < E γ < 875 MeV 875 MeV < E γ < 9 MeV 9 MeV < E < 95 MeV 95 MeV < E γ < 95 MeV γ preliminary our data Bratashevsky et al. (198) Kato et al. (198) Maid Said BnGa cosθ π

30 CBELSA/TAPS: Double pol. exp. γ p pη (J. Hartmann, Bonn) Linear photon polarization, transversally polarized target: T.4 T MeV < E γ < 75 MeV 75 MeV < E γ < 8 MeV 8 MeV < E γ < 85 MeV 85 MeV < E γ < 9 MeV T T 9 MeV < E γ < 95 MeV.5 very 95 MeV < E γ < 1 MeV MeV < E γ < 115 MeV 1 MeV < E γ < 15 MeV preliminary MeV < E γ < 1 MeV MeV < E γ < 15 MeV.5 15 MeV < E γ < 11 MeV MeV < E γ < 13 MeV our data PHOENICS data Maid Said BnGa Note: preliminary dilution factor cos θ η

31 Hadron Spectroscopy: results and ideas 1. Why baryon spectroscopy. New results and PDG related issues 3. Baryon resonance spectrum: interpretation Parity doublets and chiral symmetry AdS/QCD SU(6) O(3) Dynamically generated resonances versus C.D.D. poles 4. New results from ELSA 5. Summary

32 5. Summary Photoproduction experiments begin to make a significant impact on the spectrum of baryon resonances New data are being analyzed at Bonn, Jlab, Mainz Excellent prospects for the future The problem of missing resonances persists The dynamical reason why resonances are missing is unresolved: Chiral symmetry restoration? Are complete multiplets missing? Constituent quarks or strings?