1. 1 Overview of Spectroscopy Results in Meson Photoproduction with Polarization Observables M. Dugger, HADRON, September 2015

2. 2Outline Motivations Motivations Helicity amplitudes Helicity amplitudes Reactions and results Reactions and results PDG then and now PDG then and now M. Dugger, HADRON, September 2015

3. 3 Nucleon resonances γ p → π + n The nucleon resonance spectrum has many broad overlapping states, making disentangling the spectrum difficult  M. Dugger, HADRON, September 2015

4. 4 Resonance Rating System Nucleon resonances are rated using stars: * Poor evidence of existence **Fair evidence of existence ***Likely evidence of existence, or certain and properties need work ****Existence is certain and properties well explored M. Dugger, HADRON, September 2015

5. 5 Resonance status for N * and Δ 26 N * states: 10 with **** 5 with *** 8 with ** 3 with * Nucleon 22 Δ states: 7 with **** 3 with *** 7 with ** 5 with * Nearly half the states have only fair or poor evidence! Most states need more work to learn details Are there missing states? M. Dugger, HADRON, September 2015

6. 6Resonances Masses, widths, and coupling constants not well known for many resonances Masses, widths, and coupling constants not well known for many resonances Many models: quark model, Goldstone- boson exchange, diquark and collective models, instanton-induced interactions, flux-tube models, lattice QCD… Big Puzzle: Most models predict more resonance states than observed M. Dugger, HADRON, September 2015

7. Brief look at the non-relativistic quark model Harmonic oscillator states Non-harmonic perturbation Spin-spin hyperfine interaction including tensor part Spin-spin interactionTensor interaction M. Dugger, HADRON, September 2015

8. Oscillator + spin-spin interaction Oscillator + spin-spin + tensor interaction Brief look at the non-relativistic quark model Oscillator state: N = 1; S = 1/2,3/2; negative parity; P wave Notation: X 2S+1 L π J P, where π is permutation symmetry

9. 9 R.G. Edwards et al. Phys. Rev. D84 074508 (2011) Example: Lattice QCD results for N * resonances Mass(π) = 524 MeV Mass(π) = 396 MeV Noticeable change as the π mass becomes more realistic Number of low-lying states (boxed regions) remains the same for the two π-masses, and is the same as the non- relativistic quark model M. Dugger, HADRON, September 2015

10. 10 Low-lying Resonance States Lattice QCD is consistent with non- relativistic quark model for number of low-lying states Negative parityPositive parity Missingresonances

11. More than resonances t Born t-channel Born term: nucleon propagator t-channel: vector meson propagator The ρ 0, ω, and φ have same quantum numbers as the photon → Vector Meson Dominance The ρ 0, ω, and φ have same quantum numbers as the photon → Vector Meson Dominance The meson-NN coupling can be extracted from the Born term 11 M. Dugger, HADRON, September 2015

12. 12Outline Motivations Motivations Helicity amplitudes Helicity amplitudes Reactions and results Reactions and results PDG then and now PDG then and now M. Dugger, HADRON, September 2015

13. 13 8 helicity states: 4 initial, 2 final → 4∙2 = 8 Amplitudes are complex but parity symmetry reduces independent numbers to 8 Overall phase unobservable → 7 independent numbers HOWEVER HOWEVER, not all possible observables are linearly independent and it turns out that there must be a minimum of 8 observables / experiments Helicity amplitudes for γ + p → p + pseudoscalar helicity +1 photons (ε + ): helicity -1 photons (ε - ): Parity symmetry → Initial helicity Final helicity M. Dugger, HADRON, September 2015

14. 14 The alphabet soup of observables for pseudo-scalar photoproduction Most experiments are done with photon and/or target polarization Hyperons are “self analyzing” and allow for recoil polarization measurements without using recoil polarimeter M. Dugger, HADRON, September 2015

15. 15 Helicity amplitudes and observables for single pseudoscalar photoproduction Differential cross section Beam polarization  Target asymmetry T Recoil polarization P Double polarization observables Need at least 4 of the double observables from at least 2 groups for a “complete experiment” π 0 p, π + n, and η p will be nearly complete K + Λ will be complete! Longitudinal target Transverse target + Polarizedphotons M. Dugger, HADRON, September 2015

16. 16 Finding missing resonances requires lots of different observables. Cross sections are not enough! M. Dugger, HADRON, September 2015

17. 17Outline Motivations Motivations Helicity amplitudes Helicity amplitudes Reactions and results Reactions and results Conclusions Conclusions M. Dugger, HADRON, September 2015

18. 18 Status of CLAS meson photoproduction ✔ - published ✔ - acquired Not shown in table: Not shown in table: ω, ρ and multi-meson observables M. Dugger, HADRON, September 2015 See Priyashree Roy, Thursday at 11:05 (session 2) for ω and ρ CLAS results

19. Data from first round of double polarization measurements M. Dugger, HADRON, September 2015 Polarization observables from the proton CBELSA/TAPS

20. 20 Data There are several labs performing polarization measurements There are too many reactions and observables for me to do justice to the work that has been performed I will just show some examples of reactions specific features along with samples of data Talks at HADRON that include polarization observables: Helicity Asymmetry Measurements for π 0 photoproduction on the CLAS Frozen Spin Target: Igor Strakovsky, Thursday at 9:35 (session 1) Polarization Observables in Vector Meson Production decaying to Multi-pion-Final States using a Transversely Polarized Target and Polarized Photons at CLAS, Priyashree Roy, Thursday at 11:05 (session 2) Baryon Spectroscopy – Recent Results from the CBELSA/TAPS Experiment, Jan Hartmann, Thursday at 11:45 (session 2) Polarization Observables in η and π Production using a Polarized Target with the Crystal Ball/TAPS at MAMI, Natalie Walford, Thursday at 12:05 (session 2) Baryon spectroscopy from JLab, David Ireland, Thursday at 3:10 (plenary session) M. Dugger, HADRON, September 2015

21. 21 Isospin combinations for reactions involving π 0 and π + Δ+Δ+ N*N* Differing isospin compositions for N* and Δ + for the π 0 p and π + n final states The π 0 p and π + n final states can help distinguish between the Δ and N * M. Dugger, HADRON, September 2015

22. 22 Isospin photo-couplings Using both proton and neutron targets allows decomposition of iso-singlet and iso-vector photo-couplings C 0, C 1 γp→nπ + : γn→pπ - : Example: M. Dugger, HADRON, September 2015

23. 23 T for γ p → n π + Preliminary results CLAS results agree well with previous data G9b: FROST (new) M. Dugger, HADRON, September 2015

24. 24 F for γ p → n π + Early stage results Predictions get much worse at higher energies SAID13 are predictions based on preliminary fits to CLAS pion Σ measurements (new) G9b: FROST M. Dugger, HADRON, September 2015

25. 25 E for γ p → p π 0 ELSA results Black solid: BnGa fit Black dashed: BnGa previous to fit Blue solid: MAID Red solid: SAID (CM12) Red dashed: SAID (SN11) See Igor Strakovsky, Thursday at 9:35 (session 1) for CLAS results and more about this observable M. Gottschall et al., PRL 112, 012003 (2014)

26. 26 E for γ p → π + n S. Strauch, CLAS Collaboration, submitted to PRC Blue short dash: Julich (14E) Blue long dash: Julich (14 prediction) Green solid: SAID (st14E) Green dash-dotted: SAID (st14 prediction) Models needed data to obtain reasonable agreement See Dave Ireland, Thursday at 3:10 (plenary session) for more CLAS π observables

27. 27 M. Dugger, HADRON, September 2015 Preliminary CLAS results (Tsuneo Kageya) Deuteron target: HD- ICE Red: SAID prediction Blue: BnGa prediction E for γ n → π - p

28. 28 G for γ p → p π 0 A. Thiel et al., PRL 109, 102001 (2012) ELSA results Blue dotted: MAID Red dashed: SAID Black solid: BnGa Discrepancies between the different model predictions can be traced to the E 0+ and E 2- multipoles See Jan Hartmann’s talk (Thursday session 2) for more CBELSA/TAPS results

29. 29 “Isospin filters” isospin filters The ηp, and ωp systems have isospin ½ and limit one-step excited states of the proton to be isospin ½. Final states like ηp, ωp act as isospin filters to the resonance spectrum. γ p → π + nγ p → η p M. Dugger, HADRON, September 2015

30. 30 T and F for η photoproduction C.X. Akondi et al., PRL 113, 102001 (2014) See Natalie Walford, Thursday at 12:05 (session 2) for more about MAMI results and these observables Black circles: MAMI Pink triangles: Bonn Red dashed: MAID Green long dashed: Gissen Black dash dotted: BG2011-02 Blue dotted: SAID GE09 Black: Legendre fits Model predictions do not reproduced results of the data CLAS results coming soon

31. 31 E-observable for η photoproduction on proton I. Senderovich, CLAS Collaboration, submitted to PRL Cross section for γ n → η n shows strong enhancement in narrow region around W = 1685 MeV not seen in cross sections of γ p → η p Looking for structure near W = 1685 MeV in other observables for the γ p → η p reaction Hint of structure at W = 1685 MeV but not conclusive evidence of narrow resonance

32. Flavor-singlet Goldberger-Treiman relation m N = mass of nucleon G A (0) = nucleon flavor-singlet axial charge F = invariant decay constant (reduces to F π if U A (1) anomaly were turned off) G A (0) = 0.213 ± 0.138 Taking F = F π and N F = 3 allows a rough calculation of g GNN given g η´NN N F = Number of flavors g η´NN = η´-nucleon-nucleon coupling constant g GNN = gluon-nucleon-nucleon coupling constant The η' is the only isosinglet pseudoscalar meson. This property can be used to indirectly probe gluonic coupling to the proton The η´ isosinglet Needed to go from η 0 to physical η´ M. Dugger, HADRON, September 2015 32

33. 33 Beam asymmetry for γ p → η´ p 1. F. Huang, H. Haberzettl and K. Nakayama, Phys. Rev. C 87, 054004 (2013). 2. W.-T. Chiang, S. N. Yang, L. Tiator, M. Vanderhaegen and D. Drechsel, Phys. Rev. C 68, 045202 (2003). 3. X.-H. Zhong and Q. Zhao, Phys. Rev. C 84, 065204 (2011). 4. V. A. Tryasuchev, Phys. Part. Nucl. Lett. 10, 315 (2013). Blue dashed: [1] Red dotted: [2] Green dot-dashed: [3] Orange long dashed: [4] Black: a sin 2 θ cosθ GRAAL data: P. Levi Sandri et al., arXiv: 1407.6991v2 Predictions do not match the data CLAS data coming soon

34. 34 Photoproduction of π π p states of π π p states 64 observables 28 independent relations related to helicity amplitude magnitudes 21 independent relations related to helicity amplitude phases Results in 15 independent numbers Good for discovering resonances that decay into other resonances! M. Dugger, HADRON, September 2015

35. 35 A small sample of I s for γ p → p π 0 π 0 V. Sokhoyan, et al., CBELSA/TAPS Collaboration, Eur. Phys. J. A 51, 95 (2015) σ = σ 0 {1+ P γ [I s sin(φ) + I c cos(φ)]} CBELSA/TAPS data Much more data than shown I c not shown Black: BnGa full fit Green: BnGa without N(1900)3/2 + M. Dugger, HADRON, September 2015 Dalitz plot Clear evidence for intermediate states: Δ(1232)π N(1520)3/2 - π N(1680)5/2+ π N f 0 (980)

36. 36 N(1900)J P →N(1520)3/2 - π 0 M. Dugger, HADRON, September 2015 3/2 + 5/2 - 3/2 - 5/2 + 7/2 + JPJP Best fit V. Sokhoyan, et al., CBELSA/TAPS Collaboration, Eur. Phys. J. A 51, 95 (2015) Data from region II See Jan Hartmann’s talk (Thursday session 2) for more CBELSA/TAPS results

37. 37 Interpretation of the p π 0 π 0 data using ρ λ oscillators M. Dugger, HADRON, September 2015 L=2 L=1 ρ = (x 1 – x 2 )/sqrt(2) Antisymmetric under 1↔2 λ = (x 1 +x 2 -2x 3 )/sqrt(6) Symmetric under 1↔2 If L=2 with both ρ and λ oscillators excited, then there must be an intermediate state Resonances where only one oscillator is excited have a much reduced chance to decay into an intermediate resonance High mass resonances should have a three-particle component that excludes a simple quark-diquark picture of baryon resonances V. Sokhoyan, et al., CBELSA/TAPS Collaboration, Eur. Phys. J. A 51, 95 (2015)

38. 38 Self-analyzing reaction K + Y (hyperon) The weak decay of the hyperon allows the extraction of the hyperon polarization by looking at the decay distribution of the baryon in the hyperon center of mass system: where I is the decay distribution of the baryon, α is the weak decay asymmetry (α Λ = 0.642 and α Σ0 = -⅓ α Λ ), and P Y is the hyperon polarization. We can obtain recoil polarization information without a recoil polarimeter and the reaction is said to be “self-analyzing” M. Dugger, HADRON, September 2015

39. 39 The alphabet soup of observables for pseudo-scalar photoproduction Most experiments are done with photon and/or target polarization Hyperons are “self analyzing” and allow for recoil polarization measurements without using recoil polarimeter M. Dugger, HADRON, September 2015

40. 40 Observables C x and C z for γ p → K + Λ Without P 13 (1900) With P 13 (1900) Open circles: C z Filled circles: C x Inclusion of P 13 (1900) helped improve fit Data: R. Bradford et al., CLAS Collaboration, PRC 75, 035205 (2007) Fits: V.A. Nikonov et al., Phys. Lett. B 662, 245 (2008) M. Dugger, HADRON, September 2015

41. 41 Spin and parity of the Λ(1405) K. Moriya et al., CLAS Collaboration, Phys. Rev. Lett. 112, 082004 (2014) Reaction: γ p→K + Λ(1405) where Λ(1405) →Σ + π - 2.55 < W < 2.85 GeV and 0.6 < cos(θ c.m K+ ) < 0.9 Polarization = 0.45 Decay distribution consistent with J = 1/2 Q is the polarization transfer: Odd: independent of θ Σ Even: dependent on θ Σ odd parityeven parity J P = ½ - J P = ½ +

42. 42 T observable for γ p → K + Λ Data: Red: CLAS (preliminary from Natalie Walford) Black: Bonn78 Green GRAAL09 Models: Red: RPR-Ghent Blue: MAID Purple dashed: BnGa GRAAL and CLAS data agree fairly well More observables for this reaction and K + Σ 0 coming soon See Dave Ireland, Thursday at 3:10 (plenary session) for more CLAS hyperon observables

43. 43 New experiment coming online: BGO-OD at ELSA M. Dugger, HADRON, September 2015

44. 44 PDG: then and now Since 2010: Eight resonance states have been added: N(1685) ? ? * N(1860)5/2 + ** N(1875)3/2 - *** N(1880)1/2 + ** N(1895)1/2 - ** N(2040)3/2 + * N(2060)5/2 - ** N(2120)3/2 - ** Three resonance states have been removed: N(2080)D 13 ** N(2090)S 11 * N(2200)D 15 ** The N(1900)3/2 + has been upgraded from ** to *** The Δ(1940)3/2 - has been upgraded from * to ** M. Dugger, HADRON, September 2015

45. 45 Thanks for your time M. Dugger, HADRON, September 2015

46. 46 Title M. Dugger, HADRON, September 2015

47. 47 Title M. Dugger, HADRON, September 2015

48. 48 Temporary M. Dugger, HADRON, September 2015

49. 49 Experiment Baryon models Reaction model Amplitude analysis Linking experiment and theories cross sections spin observables LQCD quark models etc… multipole amplitudes phase shifts effective Lagrangians isobars etc… M. Dugger, HADRON, September 2015

50. 50 Circular photon beam from longitudinally- polarized electrons Incident electron beam polarization > 85% Circular beam polarization k = E γ /E e Counts H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959) M. Dugger, HADRON, September 2015

51. 51 Linearly polarized photons Coherent bremsstrahlung from 50-μ oriented diamond Two linear polarization states (vertical & horizontal) Analytical QED coherent bremsstrahlung calculation fit to actual spectrum (Livingston/Glasgow) Vertical 1.3 GeV edge shown M. Dugger, HADRON, September 2015

52. 52 FROST target FROST target Butanol composition: C 4 H 9 OH Butanol composition: C 4 H 9 OH C and O are even-even nuclei → No polarization of the bound nucleons C and O are even-even nuclei → No polarization of the bound nucleons Carbon target used to represent bound nucleon contribution of butanol Carbon target used to represent bound nucleon contribution of butanol M. Dugger, HADRON, September 2015

53. 53 Frozen spin butanol (C 4 H 9 OH) P z ≈ 80% Target depolarization: τ ≈100 days Performance: target polarization For g9a (longitudinal orientation) 10% of allocated time was used polarizing target For g9b (transverse orientation) 5% of allocated time was used polarizing target M. Dugger, HADRON, September 2015

54. 54 HDICE target HDICE target A.M. Sandorfi Deuteron+Hydrogen target Neutron and proton polarization possible M. Dugger, HADRON, September 2015

55. ✦ Look at the matrix element: ✦ Approximate the axial current as being conserved: ✦ Obtain 2 m N F(q 2 ) = q 2 G(q 2 ) ✦ Take as q → 0: G(q 2 ) → f π (1/q 2 ) g πNN, where f π is the pion decay constant and m π = 0 ✦ Goldberger-Treiman: 2 m N F(0) = f π g πNN, Note: F(0) is the isotriplet axial- vector form factor at q 2 = 0 ✦ Do the same calculation for the flavor singlet axial current to get: 2 m N G A (0) = f g η0NN, where η 0 is the unphysical flavor singlet goldstone boson Goldberger-Treiman M. Dugger, HADRON, September 2015

56. Why do baryon spectroscopy ? Continuous spectrum Absorption spectrum Emission spectrum Atomic spectroscopy: H + γ → H* → H + γ Intensity vs. wavelength Atomic spectroscopy was a very useful tool in determining the quantum description of the atom. Quantum mechanics for H* → H + γ reproduces the observed spectrum Ne + H Ne Only 350nm700nm n1n1 n4n4 n3n3 n2n2 Baryon models must also be tested experimentally M. Dugger, HADRON, September 2015

57. 57 pi0 beam asymmetry M. Dugger, HADRON, September 2015

58. 58 γ p → p π π γ p → p π π Next slide Linear beam and unpolarized target: Λ i = δ ʘ = 0 M. Dugger, HADRON, September 2015

59. 59 Conclusion M. Dugger, HADRON, September 2015

60. 60 Title M. Dugger, HADRON, September 2015