1. M. Dugger, Jlab User Meeting, June 2012 1 First data with FROST First data with FROST Michael Dugger* Arizona State University *Work at ASU is supported by the U.S. National Science Foundation

2. M. Dugger, Jlab User Meeting, June 2012 2Outline General motivations General motivations Polarization observables to be discussed Polarization observables to be discussed Experimental details Experimental details Preliminary results for several polarization observables Preliminary results for several polarization observables Conclusions Conclusions

3. M. Dugger, Jlab User Meeting, June 2012 3 Motivation: Baryon resonances Masses, widths, and coupling constants not well known for many resonances Masses, widths, and coupling constants not well known for many resonances Many models: relativised 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

4. M. Dugger, Jlab User Meeting, June 2012 4 Observables to be shown Observables to be shown γ p → p π 0 E γ p → n π + E, G γ p → p η E γ p → K + Λ E, Σ, G γ p → K + Σ 0 E γ p → p π + π - I s, P z, P ○ z Single pseudoscalar photoproduction

5. M. Dugger, Jlab User Meeting, June 2012 5 Isospin overlaps for reactions involving π 0 and π + Δ+Δ+ N* Differing isospin overlaps of 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*

6. M. Dugger, Jlab User Meeting, June 2012 6 “Isospin filters” Resonance spectrum has many broad overlapping states isospin filters The ηp and K + Λ systems have isospin ½ and limit one-step excited states of the proton to be isospin ½. The final states ηp and K + Λ act as isospin filters to the resonance spectrum. γ p → π + nγ p → η p

7. M. Dugger, Jlab User Meeting, June 2012 7 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 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 Yi is the hyperon polarization. We can obtain recoil polarization information without a recoil polarimeter and the reaction is said to be “self-analyzing”

8. M. Dugger, Jlab User Meeting, June 2012 8 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 HOWEVERHOWEVER, 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

9. M. Dugger, Jlab User Meeting, June 2012 9 Helicity amplitudes and observables for single pseudoscalar photoproduction Differential cross section Beam polarization Target asymmetry Recoil polarization 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! g9a g9b

10. M. Dugger, Jlab User Meeting, June 2012 10 Photoproduction of π + π - p states 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!

11. M. Dugger, Jlab User Meeting, June 2012 11 Cross sections are not enough. Finding missing resonances requires lots of different observables. Cross sections are not enough.

12. M. Dugger, Jlab User Meeting, June 2012Outline General motivations Polarization observables to be discussed Polarization observables to be discussed Experimental details Experimental details Preliminary results for several polarization observables Preliminary results for several polarization observables Conclusions Conclusions

13. M. Dugger, Jlab User Meeting, June 2012 13 Bremsstrahlung photon tagger Jefferson Lab Hall B bremsstrahlung photon tagger E γ = 20-95% of E 0 E γ up to ~5.5 GeV Circular polarized photons with longitudinally polarized electrons Circular polarized photons with longitudinally polarized electrons Oriented diamond crystal for linearly polarized photons Oriented diamond crystal for linearly polarized photons 61 backing counters

14. M. Dugger, Jlab User Meeting, June 2012 14 Circular photon beam from longitudinally polarized electrons Electron beam polarization > 85% Circular beam polarization k = E γ /E e Counts H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959)

15. M. Dugger, Jlab User Meeting, June 2012 15 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 very preliminary Currently, only very preliminary values of P γ

16. M. Dugger, Jlab User Meeting, June 2012 16 FROST in Hall B FROST in Hall B

17. M. Dugger, Jlab User Meeting, June 2012 17 FROST target FROST target Butanol composition: C 4 H 9 OH Butanol composition: C 4 H 9 OH Each bound proton is paired with a bound neutron → No polarization of the bound nucleons Each bound proton is paired with a bound neutron → 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

18. M. Dugger, Jlab User Meeting, June 2012 18 Frozen spin butanol (C 4 H 9 OH) P z ≈ 80% Target depolarization: τ ≈100 days 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

19. M. Dugger, Jlab User Meeting, June 2012 19 S. Strauch

20. M. Dugger, Jlab User Meeting, June 2012 20 FROST running conditions g9a: First running of FROSTg9b: Second running of FROST Longitudinally polarized target Circular and linear photon polarization Transversely polarized target Circular and linear photon polarization

21. M. Dugger, Jlab User Meeting, June 2012 21Outline General motivations Polarization observables to be discussed Polarization observables to be discussed Experimental details Preliminary results for several polarization observables Preliminary results for several polarization observables Conclusions

22. M. Dugger, Jlab User Meeting, June 2012 22 Dilution factor and helicity asymmetry E Dilution factor and helicity asymmetry E Theoretically: Experimentally: → where Y represents yield and d is the dilution, which is the ratio of hydrogen events to total events: Note: Bound nucleons have no polarization → E bound = 0

23. M. Dugger, Jlab User Meeting, June 2012 23 γ p → p η γ p → p η Arizona State University Brian Morrison, Michael Dugger, and Barry Ritchie

24. M. Dugger, Jlab User Meeting, June 2012 24 Helicity asymmetry for η photoproduction at threshold Helicity asymmetry for η photoproduction at threshold S 11 (1535) dominates at threshold Since the S 11 (1535) is an L=0, s = ½, resonance, this resonance can only couple to helicity = ½ initial state. S 11 dominance forces E ≈ 1.0 at, and near, threshold for all scattering angles Provides an analytic check

25. M. Dugger, Jlab User Meeting, June 2012 Scale factors γ p →p π + π - X Scale factors = Butanol/Carbon Carbon Butanol Bound nucleon events z (cm) m 2 X (GeV 2 ) Counts

26. M. Dugger, Jlab User Meeting, June 2012 N 1/2 + N 3/2 N 1/2 - N 3/2 Scaled carbon W = 1525 MeV cos(θ c.m. ) = -0.3 Sample η fits from γ p → p X m X (GeV) Counts

27. M. Dugger, Jlab User Meeting, June 2012 E at threshold for p η ☺ SAID MAID Bonn-Gatchina PRELIMINARY PRELIMINARY PRELIMINARY PRELIMINARY γ+ p → p + X p 0 = 1.00 ± 0.04 γ + p → p + X (n.c.) p 0 = 1.02 ± 0.04 γ + p → p + X (γ det.) p 0 = 0.99 ± 0.04 γ + p → p + X (γ det. n.c.) p 0 = 0.98 ± 0.04 *n.c. implies no charged particles other than the proton. cos(θ c.m. ) W = 1525 MeV All have E=1, within statistical uncertainties

28. M. Dugger, Jlab User Meeting, June 2012 28 Helicity asymmetry at fixed energies Helicity asymmetry at fixed energies SAID MAID Bonn-Gatchina PRELIMINARY PRELIMINARYPRELIMINARY PRELIMINARY PRELIMINARYPRELIMINARY PRELIMINARYPRELIMINARYPRELIMINARY Preliminary data prefers SAID for W >1.75 GeV E cos(θ c.m. )

29. M. Dugger, Jlab User Meeting, June 2012 29 γ p → π + n γ p → π + n University of South Carolina Steffen Strauch

30. M. Dugger, Jlab User Meeting, June 2012 30 E: γ p→π + n for W = 1.25 to 1.70 GeV PreliminaryDataPreliminaryData

31. M. Dugger, Jlab User Meeting, June 2012 31 E: γ p → π + n for W = 1.70 to 2.25 GeV For W> 1.75 GeV none of the models represents the data well. For W< 1.75 GeV all of the models represent the data fairly well. Preliminary Data

32. M. Dugger, Jlab User Meeting, June 2012 32 γ p → p π 0 γ p → p π 0 The George Washington University Hideko Iwamoto and Bill Briscoe

33. M. Dugger, Jlab User Meeting, June 2012 First data with FROST W = 1.433 GeV W = 1.465 GeV W = 1.497 GeV W = 1.588 GeVW = 1.558 GeVW = 1.528 GeV

34. M. Dugger, Jlab User Meeting, June 2012 34 First data with FROST W = 1.617 GeVW = 1.646 GeV W = 1.674 GeVW = 1.702 GeV W = 1.730 GeV W = 1.809 GeV W = 1.783 GeVW = 1.756 GeV

35. M. Dugger, Jlab User Meeting, June 2012 First data with FROST W = 1.835 GeV W = 1.860 GeV W = 1.885 GeVW = 1.910 GeVW = 1.934 GeV W = 2.041 GeV W = 1.994 GeV W = 1.959 GeV Agreement with models breaks down for W > 1850 MeV

36. M. Dugger, Jlab User Meeting, June 2012 36 γ p → K + Λ and γ p→ K + Σ 0 γ p → K + Λ and γ p→ K + Σ 0 Catholic University of America Liam Casey and Franz Klein

37. M. Dugger, Jlab User Meeting, June 2012 37 Helicity asymmetry E for K + Λ Helicity asymmetry E for K + Λ

38. M. Dugger, Jlab User Meeting, June 2012 38 Helicity asymmetry for K + Λ Helicity asymmetry for K + Λ None of the models represents the data well None of the models represents the data well

39. M. Dugger, Jlab User Meeting, June 2012 39 Helicity asymmetry for K + Σ 0 Helicity asymmetry for K + Σ 0 Models represents the data better than for K + Λ Models represents the data better than for K + Λ

40. M. Dugger, Jlab User Meeting, June 2012 40 Σ and G observables Σ and G observables Σ is a single polarization observable (beam asymmetry) G is a double polarization observable

41. M. Dugger, Jlab User Meeting, June 2012 41 γ p → π + n γ p → π + n The University of Edinburgh Jo McAndrews and Dan Watts

42. M. Dugger, Jlab User Meeting, June 2012 Create an asymmetry and fit a function to obtain G: Asymmetry +ve polarised target G Observable Extraction PRELIMINARY! p3 = p γ p z fG Example of extraction for G for π + n Example of extraction for G for π + n Asymmetry -ve polarised target

43. M. Dugger, Jlab User Meeting, June 2012 Preliminary results of G for π + n PRELIMINARY Early stage results with very preliminary linear beam polarization values

44. M. Dugger, Jlab User Meeting, June 2012 44 γ p → K + Λ University of Glasgow Stuart Fegan and Ken Livingston

45. M. Dugger, Jlab User Meeting, June 2012 45 Σ for K + Λ Σ for K + Λ Since the beam asymmetry Σ does not rely upon target polarization, bound nucleons can have Σ ≠ 0 Dilution must be carefully determined The beam asymmetry is used only for purposes of checking data consistency PRELIMINARY

46. M. Dugger, Jlab User Meeting, June 2012 46 P γ P z G for K + Λ P γ P z G for K + Λ E γ = 1.5 GeV Can clearly see sign change between +z and –z target polarization data PRELIMINARY

47. M. Dugger, Jlab User Meeting, June 2012 47 γ p → p π + π - γ p → p π + π - Florida State University Sungkyun Park and Volker Crede

48. M. Dugger, Jlab User Meeting, June 2012 48 γ p → p π + π - γ p → p π + π -

49. M. Dugger, Jlab User Meeting, June 2012 49 γ p → p π + π - γ p → p π + π -

50. M. Dugger, Jlab User Meeting, June 2012 50 I S for p π + π - I S for p π + π - φπ+φπ+

51. M. Dugger, Jlab User Meeting, June 2012 51 P ○ z for p π + π - P ○ z for p π + π - φπ+φπ+

52. M. Dugger, Jlab User Meeting, June 2012 52 P z for p π + π - P z for p π + π - φπ+φπ+

53. M. Dugger, Jlab User Meeting, June 2012 53 P z for p π + π - P z for p π + π - φπ+φπ+

54. M. Dugger, Jlab User Meeting, June 2012 54 FROzen Spin Target “FROST” (g9b) Transversely polarized target  Transversely polarized target Beam: Circular polarization; Linear polarization; Un-polarized FT (for pseudoscalars) Data obtained for Σ, F, H, P and T (for pseudoscalars) Data is in calibration phase right now Data is in calibration phase right now BeamTargetObservable σ 0 = unpolarized cross section, P T = transverse beam polarization P 0 = circular polarization, P z = longitudinal target polarizaion CircularTransverse Linear Transverse

55. M. Dugger, Jlab User Meeting, June 2012 55 A very early look at T for γ p → π + n A very early look at T for γ p → π + n Arizona State University Michael Dugger and Barry Ritchie

56. M. Dugger, Jlab User Meeting, June 2012 56 A quick attempt at T from uncalibrated CLAS data A quick attempt at T from uncalibrated CLAS data Used only 2 uncalibrated runs E γ from 0.65 to 1.2 GeV cos(θ π c.m. ) = 0.95 Target offset (in φ) is within one standard deviation of the set value (- 60 degrees) The measured value of T is within 1.14 standard deviations of SAID T SAID = -0.440 T = -0.34 ± 0.09

57. M. Dugger, Jlab User Meeting, June 2012 57 Conclusion Conclusion Models fit preliminary FROST pion helicity asymmetry data best when W < 1.75 GeV Preliminary FROST helicity asymmetry data for η p favors SAID for W > 1.75 GeV None of the models shown represents the K + Λ data well but do much better for K + Σ 0 Σ and G measurements are at an early stage of analysis and use very preliminary linear beam polarization values, but are progressing nicely lots There is lots of data for the π + π - p channel, and the preliminary I S observable from FROST compares well with g8b Very preliminary looks at data from the second running of FROST (transverse target) are promising

58. M. Dugger, Jlab User Meeting, June 2012 58 Acknowledgements ✦ NSF ✦ DOE ✦ CLAS Collaboration