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*Work at ASU is supported by the U.S. National Science Foundation

Latest results from FroST at Jefferson Lab. Barry G. Ritchie* Arizona State University. *Work at ASU is supported by the U.S. National Science Foundation. Nucleon excited states. As a composite system, the nucleon has a specific spectrum of excitations: the nucleon resonances .

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*Work at ASU is supported by the U.S. National Science Foundation

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

  2. Nucleon excited states • 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.  γ p →π+ n B. G. Ritchie - MENU 2013 - October 2013

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

  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. Example: Lattice QCD results for N*resonances • Noticeable change as the πmassbecomes 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. mπ = 524 MeV mπ = 391 MeV Example: R.G. Edwards et al. Phys. Rev. D87 054506 (2013) B. G. Ritchie - MENU 2013 - October 2013

  6. Solving a mystery: “The Case of the Missing Resonances” Experiment cross sections, spin observables Amplitude analysis Reaction model multipole amplitudes, phase shifts effective Lagrangians, Isobars, etc… Baryon models LQCD, quark models, etc… B. G. Ritchie - MENU 2013 - October 2013

  7. Gathering clues: helicity amplitudes B. G. Ritchie - MENU 2013 - October 2013

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

  9. Linkage between helicity amplitudes and the observables for single pseudoscalar photoproduction Differential cross section Beam polarization S 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” • π0p, π+ n, and η p will be nearly complete • K+Λ will be complete! Longitudinal target Transverse target + Polarized photons B. G. Ritchie - MENU 2013 - October 2013

  10. Conducting the investigation FroST g9b g9a B. G. Ritchie – MENU 2013 – Rome

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

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

  13. Hall B Bremsstrahlung Photon Tagger (not dead yet!) • Jefferson Lab Hall B bremsstrahlung photon tagger had: • Eγ= 20-95% of E0 • Eγup to ~5.5 GeV • Circular polarized photons with longitudinally polarized electrons • Oriented diamond crystal for linearly polarized photons 61 backing counters B. G. Ritchie - MENU 2013 - October 2013

  14. Frozen Spin Target - FroST • 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 B. G. Ritchie - MENU 2013 - October 2013

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

  16. FroST performance • Frozen spin butanol (C4H9OH) • Pz≈ 80% • Target depolarization: τ ≈100 days • 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. FroST’s first clues: Single pion photoproduction B. G. Ritchie - MENU 2013 - October 2013

  18. Isospin combinations for reactions involving π0 and π+ • Differing isospin compositions for N* and Δ+ for the π0 p and π+ n final states • Theπ0 p andπ+n final states can help distinguish between the Δand N* Δ+ N* B. G. Ritchie - MENU 2013 - October 2013

  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 Σdata included. B. G. Ritchie - MENU 2013 - October 2013

  20. Observables: T and F Reaction: γp →n π+ • Configuration: • Circular photon polarization • Transverse target polarization • Unpolarized photon (add circular beams) • No recoil polarization • Experiment: • g9b: FroST B. G. Ritchie - MENU 2013 - October 2013

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

  22. F for γ p → n π+ (new) (new) g9b: Michael Dugger • Early stage results • Predictions get much worse at higher energies • SAID13 are predictions based on preliminary fits to CLAS pion Σ measurements (new) B. G. Ritchie - MENU 2013 - October 2013

  23. Observable: E Reactions: γ p → p π0 and γ p → n π+ • Configuration: • Circular photon polarization • Longitudinal target polarization • No recoil polarization • Experiment: • g9a: FroST B. G. Ritchie - MENU 2013 - October 2013

  24. E for γ p → p π0 g9a: Michael Dugger (new) • Early stage results • Predictions better at lower energies B. G. Ritchie - MENU 2013 - October 2013

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

  26. Observable: GReactions: γp → n π+ • Configuration: • Linear photon polarization • Longitudinal target polarization • No recoil polarization • Experiment: • g9a: FroST B. G. Ritchie - MENU 2013 - October 2013

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

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

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

  30. Observables: T and F Reaction: γp →η p • Configuration: • Circular photon polarization • Transverse target polarization • Unpolarized photon (add circular beams) • No recoil polarization • Experiment: • g9b: FroST B. G. Ritchie - MENU 2013 - October 2013

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

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

  33. Observable: E Reaction: γp →η p • Configuration: • Circular photon polarization • Longitudinal Target polarization • No recoil polarization • Experiment: • g9a: FROST B. G. Ritchie - MENU 2013 - October 2013

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

  35. Observables: T and F Reaction: γp →K+L and γ p →K0S+ g9b: • Configuration: • Circular photon polarization • Transverse target polarization • Unpolarized photon (add circular beams) • No recoil polarization Natalie Walford B. G. Ritchie - MENU 2013 - October 2013

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

  37. T for γp →K0S+ Bonn-Gatchina: blue kaonMAID: pink W=1725 MeV Eγ=1117 MeV W=1875 MeV Eγ=1405 MeV W=1775 MeV Eγ=1210 MeV W=1825 MeV Eγ=1306 MeV Preliminary W=2075 MeV Eγ=1826 MeV W=1925 MeV Eγ=1506 MeV W=1975 MeV Eγ=1610 MeV W=2025 MeV Eγ=1717 MeV W=2275 MeV Eγ=2290 MeV W=2225 MeV Eγ=2170 MeV W=2175 MeV Eγ=2053 MeV W=2125 MeV Eγ=1938 MeV

  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 Iis the decay distribution of the baryon, α is the weak decay asymmetry (αΛ= 0.642 and αΣ0 = -⅓ αΛ), and PYis 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. More clues from FroST: multi-pion photoproduction B. G. Ritchie - MENU 2013 - October 2013

  40. Photoproduction 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. γ p → p π+π- unpolarized beam and longitudinal target: δl = Λx = Λy = 0 next slide slide after next longitudinal beam and longitudinal target: δl≠ 0, Λx = Λy = 0 B. G. Ritchie - MENU 2013 - October 2013

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

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

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

  45. Conclusions • 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 B. G. Ritchie - MENU 2013 - October 2013

  46. Conclusions (cont’d) • For K Λand K Σchannels, 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! B. G. Ritchie - MENU 2013 - October 2013

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

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

  49. Circular beam polarization Circular polarization from 100% polarized electron beam Circular polarization Counts • Circular photon beam from longitudinally- polarized electrons • Incident electron beam polarization • > 85% k = Eγ/Ee H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959) B. G. Ritchie - MENU 2013 - October 2013

  50. Linearly polarized photons • Coherent bremsstrahlung from 50-μoriented 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

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