1. B. G. Ritchie - MENU 2013 - October 2013 1 *Work at ASU is supported by the U.S. National Science Foundation Barry G. Ritchie* Arizona State University Latest results from FroST at Jefferson Lab at Jefferson Lab

2. 2 Nucleon excited states γ p → π + n B. G. Ritchie - MENU 2013 - October 2013 As a composite system, the nucleon has a specific spectrum of excitations: the nucleon resonances. This nucleon resonance spectrum has many broad overlapping states, making disentangling the spectrum difficult. 

3. B. G. Ritchie - MENU 2013 - October 2013 3 The state of our knowledge 22 Δ * states: 7 with **** 3 with *** 7 with ** 5 with * Nucleon Nearly half the states have only fair or poor evidence! Most states need more work to learn details Are there missing states? 26 N * states: 10 with **** 5 with *** 8 with ** 3 with *

4. 4 Models predict (lots of)excitations Many nucleon models have offered “predictions” for the nucleon resonance spectrum -- constituent quark model diquark collective models instanton-induced interactions flux-tube models lattice QCD (your favorite here) - BUT… THE BIG MYSTERY: Most models predict many more resonance states than have been observed. B. G. Ritchie - MENU 2013 - October 2013

5. 5 Example: R.G. Edwards et al. Phys. Rev. D87 054506 (2013) Example: Lattice QCD results for N * resonances 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 generally is the same as NRQMs Many of these predicted states are poorly determined or missing. m π = 524 MeV m π = 391 MeV

6. EXPERIMENT BARYON MODELS REACTION MODEL AMPLITUDE ANALYSIS cross sections, spin observables multipole amplitudes, phase shifts effective Lagrangians, Isobars, etc… 6 Solving a mystery: “The Case of the Missing Resonances” LQCD, quark models, etc… B. G. Ritchie - MENU 2013 - October 2013

7. 7 Gathering clues: helicity amplitudes

8. 8 8 helicity states: 4 initial, 2 final → 4∙2 = 8 possible complex amplitudes Parity reduces these to 4 complex amplitudes H i (8 W-dependent functions) Overall phase unobservable → 7 W-dependent functions Suggests complete determination possible with 7 observables/experiments HOWEVER HOWEVER, not all possible observables are linearly independent → a minimum of 8 observables / experiments Helicity amplitudes for γ + p → p + pseudoscalar helicity +1 photons (ε + ): helicity -1 photons (ε - ): → Parity → Initial helicity final helicity B. G. Ritchie - MENU 2013 - October 2013

9. 9 Linkage between helicity amplitudes and the 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 + B. G. Ritchie - MENU 2013 - October 2013

10. Conducting the investigation B. G. Ritchie – MENU 2013 – Rome 10 Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E FroST g9b g9a

11. 11 B. G. Ritchie - MENU 2013 - October 2013 The detective’s tools: FroST and friends

12. CLAS (1997-2012) Lest we forget: CLAS was very good for detecting charged particles CLAS had large acceptance 12 B. G. Ritchie - MENU 2013 - October 2013

13. 13 Hall B Bremsstrahlung Photon Tagger (not dead yet!) 61 backing counters B. G. Ritchie - MENU 2013 - October 2013 Jefferson Lab Hall B bremsstrahlung photon tagger had: E γ = 20-95% of E 0 E γ up to ~5.5 GeV Circular polarized photons with longitudinally polarized electronsCircular polarized photons with longitudinally polarized electrons Oriented diamond crystal for linearly polarized photonsOriented diamond crystal for linearly polarized photons

14. B. G. Ritchie - MENU 2013 - October 2013 14 Doped butanol and dynamic nuclear polarization): Butanol with paramagnetic radical TEMPO Polarize unpaired TEMPO electrons to 99.999% with B = 5 T and T = 0.3 K Transfer electron polarization to free protons with microwaves at ~140 GHz Remove microwaves Cool to T = 30 mK and use B = 0.5 T holding field Put target in CLAS and run experiment Frozen Spin Target - FroST Frozen Spin Target - FroST

15. B. G. Ritchie – MENU 2013 - Rome 15 Transverse polarization – g9b Longitudinal polarization – g9a Complete assembly – g9a Holding coils

16. 16 Frozen spin butanol (C 4 H 9 OH) P z ≈ 80% Target depolarization: τ ≈100 days FroST performance For g9a (longitudinal orientation) 10% of allocated time was used polarizing target For g9b (transverse orientation) 5% of allocated time was used polarizing target B. G. Ritchie - MENU 2013 - October 2013

17. 17 FroST’s first clues: Single pion photoproduction

18. 18 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 * B. G. Ritchie - MENU 2013 - October 2013

19. 19 Theoretical analyses In the plots that follow, you will see many curves from: SAID: A two-stage PWA where stage 1 is the fit to data stage 2 is the extraction of resonance parameters BnGa (Bonn-Gatchina): A single stage PWA MAID: Isobar analysis Note: The SAID results labeled “new” in this section of the talk include the new Σ data from ASU/CLAS. Later sections of the talk show SAID results that do not have the new Σ data included.

20. 20 Observables: T and F Observables: T and F B. G. Ritchie - MENU 2013 - October 2013 Experiment: g9b: FroST Configuration: Circular photon polarization Circular photon polarization Transverse target polarization Transverse target polarization Unpolarized photon (add circular beams) No recoil polarization Reaction: γ p → n π + Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E

21. B. G. Ritchie - MENU 2013 - October 2013 21 T for γ p → n π + Early stage results CLAS results agree well with previous data (new) g9b: Michael Dugger

22. B. G. Ritchie - MENU 2013 - October 2013 22 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: Michael Dugger

23. 23 Observable: E Observable: E B. G. Ritchie - MENU 2013 - October 2013 Configuration: Circular photon polarization Circular photon polarization Longitudinal target polarization Longitudinal target polarization No recoil polarization Reactions : γ p → p π 0 and γ p → n π + Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E Experiment: g9a: FroST

24. B. G. Ritchie - MENU 2013 - October 2013 24 E for γ p → p π 0 Early stage results Predictions better at lower energies (new) g9a: Michael Dugger

25. B. G. Ritchie - MENU 2013 - October 2013 25 E for γ p → n π + Steffen Strauch PRELIMINARY Predictions worse at higher energies SAID SAID (new) MAID Cos(θ π c.m. ) W = 1.25 GeV W = 1.27 GeV W = 1.29 GeVW = 1.31 GeVW = 1.33 GeVW = 1.35 GeV W = 1.47 GeVW = 1.45 GeV W = 1.43 GeVW = 1.41 GeVW = 1.39 GeVW = 1.37 GeV W = 1.49 GeV W = 1.51 GeV W = 1.53 GeVW = 1.55 GeVW = 1.57 GeVW = 1.59 GeV W = 1.71 GeVW = 1.69 GeV W = 1.67 GeVW = 1.65 GeV W = 1.63 GeV W = 1.61 GeV W = 1.73 GeV W = 1.75 GeVW = 1.77 GeVW = 1.81 GeVW = 1.83 GeV W = 1.9 GeV W = 2.19 GeVW = 2.13 GeVW = 2.07 GeV W = 2.02 GeVW = 1.98 GeVW = 1.94 GeV g9a:

26. 26 Observable: G Reactions: γ p → n π + Observable: G Reactions: γ p → n π + B. G. Ritchie - MENU 2013 - October 2013 Configuration: Linear photon polarization Linear photon polarization Longitudinal target polarization Longitudinal target polarization No recoil polarization Experiment: g9a: FroST Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E

27. B. G. Ritchie - MENU 2013 - October 2013 27 G for γ p → n π + g9a: ▬ SAID -- MAID - Bonn-Gatch Jo McAndrew PRELIMINARY W=2030-2080 MeV W=1640-1680 MeV W=1840-1880 MeV W=1475-1500 MeV Early stage results Photon polarizations are approximate ◊ Bussey et al

28. B. G. Ritchie - MENU 2013 - October 2013 28 Additional clues from FroST: Single eta or kaon photoproduction

29. 29 “Isospin filters” Final states of ηp and K + Λ systems have isospin ½, and limit one-step excited states of the proton to be isospin ½. isospin filters Thus, the final states ηp and K + Λ can serve as isospin filters to the resonance spectrum. γ p → π + nγ p → η p B. G. Ritchie - MENU 2013 - October 2013

30. 30 Observables: T and F Observables: T and F B. G. Ritchie - MENU 2013 - October 2013 Configuration: Circular photon polarization Circular photon polarization Transverse target polarization Transverse target polarization Unpolarized photon (add circular beams) No recoil polarization Reaction: γ p → η p Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E Experiment: g9b: FroST

31. B. G. Ritchie – MENU 2013 – Rome 31 T for γ p → η p g9b: Ross Tucker

32. B. G. Ritchie – MENU 2013 – Rome 32 F for γ p → η p g9b: Ross Tucker

33. 33 Observable: E Observable: E B. G. Ritchie - MENU 2013 - October 2013 Configuration: Circular photon polarization Circular photon polarization Longitudinal Target polarization Longitudinal Target polarization No recoil polarization Reaction : γ p → η p Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E Experiment: g9a: FROST

34. B. G. Ritchie - MENU 2013 - October 2013 34 E for γ p →  p Predictions are generally inconsistent with data at all energies at more forward angles (new) g9a: Igor Senderovich

35. 35 Observables: T and F Observables: T and F B. G. Ritchie - MENU 2013 - October 2013 Configuration: Circular photon polarization Circular photon polarization Transverse target polarization Transverse target polarization Unpolarized photon (add circular beams) No recoil polarization Reaction: γ p → K +  and γ p → K 0   Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E Photon beamTarget xyz Unpolarized0T0 Linearly polarizedH(-P)-G Circularly polarizedF0-E g9b: Natalie Walford

36. W=1725 MeV E γ =1117 MeV W=2125 MeV E γ =1938 MeV W=2025 MeV E γ =1717 MeV W=1975 MeV E γ =1610 MeV W=1925 MeV E γ =1506 MeV W=1875 MeV E γ =1405 MeV W=1825 MeV E γ =1306 MeV W=1775 MeV E γ =1210 MeV W=2275 MeV E γ =2290 MeV W=2225 MeV E γ =2170 MeV W=2175 MeV E γ =2053 MeV W=1675 MeV E γ =1027 MeV T for γ p → K +  Bonn-Gatchina: blue kaonMAID: pink Bonn –data - purple GRAAL data - black

37. W=1725 MeV E γ =1117 MeV W=2125 MeV E γ =1938 MeV W=2075 MeV E γ =1826 MeV W=2025 MeV E γ =1717 MeV W=1975 MeV E γ =1610 MeV W=1925 MeV E γ =1506 MeV W=1875 MeV E γ =1405 MeV W=1825 MeV E γ =1306 MeV W=1775 MeV E γ =1210 MeV W=2275 MeV E γ =2290 MeV W=2225 MeV E γ =2170 MeV W=2175 MeV E γ =2053 MeV T for γ p → K 0   Bonn-Gatchina: blue kaonMAID: pink

38. 38 A “complete” set of clues: Self-analyzing reaction K + Y (hyperon) Hyperon weak decay allows extraction of 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. Get recoil polarization information without a recoil polarimeter: the reaction is “self-analyzing”. No preliminary results yet, but data will be forthcoming. B. G. Ritchie - MENU 2013 - October 2013

39. 39 More clues from FroST: multi-pion photoproduction

40. 40 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! B. G. Ritchie - MENU 2013 - October 2013

41. 41 γ p → p π + π - γ p → p π + π - B. G. Ritchie - MENU 2013 - October 2013 next slide unpolarized beam and longitudinal target: δ l = Λ x = Λ y = 0 slide after next longitudinal beam and longitudinal target: δ l ≠ 0, Λ x = Λ y = 0

42. Spin observable P z for γ p → p π + π - B. G. Ritchie – MENU 2013 – Rome 42 g9a: Sungkyun Park FSU: Winston Roberts Fix & Arenhövel PRELIMINARY

43. Spin observable P z for γ p → p π + π - B. G. Ritchie – MENU 2013 – Rome 43 Fix & Arenhövel s Yuqing Mao g9a: PRELIMINARY

44. 44 FroST results in the full CLAS program for photoproduction from proton ✔ - published ✔ - acquired Not shown in table: Not shown in table: ω and ππ photoproduction observables Preliminary results shown in this talk

45. B. G. Ritchie - MENU 2013 - October 2013 45Conclusions Spin observables will tremendously aid in sleuthing out resonance parameters and finding missing resonances (if they exist) Photon experiments in Hall-B with FroST at JLab have acquired hundreds of data points yielding clues to the missing resonances For most reaction channels, we will have data sufficient for a nearly complete experiment

46. B. G. Ritchie - MENU 2013 - October 2013 46 Conclusions (cont’d) For K Λ and K Σ channels, we will have a complete experiment Double-pion observables offer a “next generation” probe of reaction mechanisms and resonances Data for some reactions and some observables are nearing the publication stage, but much work remains – STAY ON THE CASE!

47. B. G. Ritchie - MENU 2013 - October 2013 47Acknowledgements

48. B. G. Ritchie – MENU 2013 - Rome 48 Molte grazie!

49. 49 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) B. G. Ritchie - MENU 2013 - October 2013

50. 50 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 B. G. Ritchie - MENU 2013 - October 2013

51. 51 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 B. G. Ritchie - MENU 2013 - October 2013

52. 52 Slide from Chris Keith FroST target

53. B. G. Ritchie - MENU 2013 - October 2013 53 Slide from Chris Keith FroST target

54. B. G. Ritchie - MENU 2013 - October 2013 54 Slide from Chris Keith FroST target

55. B. G. Ritchie - MENU 2013 - October 2013 55 Slide from Chris Keith FroST target

56. B. G. Ritchie - MENU 2013 - October 2013 56 Slide from Chris Keith