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Compton Scattering at HIGS with Polarized Photons

Compton Scattering at HIGS with Polarized Photons. Compton@HIGS Collaboration. George Washington University Jerry Feldman Mark Sikora Duke University/TUNL Luke Myers Henry Weller Mohammad Ahmed Jonathan Mueller Seth Henshaw. University of Kentucky Mike Kovash. Outline.

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Compton Scattering at HIGS with Polarized Photons

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  1. Compton Scattering at HIGS with Polarized Photons Compton@HIGS Collaboration • George Washington University • Jerry Feldman • Mark Sikora • Duke University/TUNL • Luke Myers • Henry Weller • Mohammad Ahmed • Jonathan Mueller • Seth Henshaw • University of Kentucky • Mike Kovash

  2. Outline • What (and where) is HIGS? • What have we done so far at HIGS? • polarized Compton scattering study of IVGQR • elastic Compton scattering on 6Li • high energy (60-86 MeV) and low energy (3-5 MeV) • What are we planning to do at HIGS? • elastic Compton scattering on deuterium • neutron polarizability • polarized Compton scattering on proton • proton electric polarizability • double-polarized Compton scattering on proton • proton spin polarizability

  3. Background Information on HIGS

  4. United States

  5. North Carolina

  6. Duke University

  7. TUNL HIGS TUNL Triangle Universities Nuclear Laboratory

  8. Duke Free-Electron Laser Lab

  9. RF Cavity Optical Klystron FEL Booster Injector Mirror LINAC Storage Ring and Booster Circularly and linearly polarized g rays, nearly monoenergetic (Eg= 2–90 MeV) Utilizes Compton backscattering to generate g rays

  10. HIGS Photon Beam to target room

  11. HIGS Photon Beam • monoenergetic photons up to ~90 MeV • energy will reach ~160 MeV by 2015 • 100% linear or circular polarization • high photon beam intensity • ~107 Hz at 20-60 MeV • ~108 Hz below 15 MeV • low beam-related background • no bremsstrahlung typical of tagged photons

  12. Polarized Compton Scatteringfor IVGQR Systematics

  13. DT = 0 DT = 1 L = 1 L = 2 Giant Resonances • collective nuclear excitations • GDR and ISGQR well known • IVGQR poorly known • photon as isovector probe • use pol. photons for IVGQR • map systematics vs. A • nuclear symmetry energy • neutron star eqn. of state • ratio of H/V scattered photons is sensitive to E1/E2 interference • sign difference in interference term at forward/backward angles

  14. Photon Asymmetry in IVGQR E1/E2 interference pure E1

  15. HINDA Array HIGS NaI Detector Array 55o 55o 125o 125o

  16. 209Bi Results for 209Bi

  17. Results for 89Y • extend measurements to 89Y • measured 124Sn last month! • lease 142Nd target from ORNL for $15k • other targets include A ~ 56, 180, 238 89Y preliminary

  18. Results for 124Sn

  19. IVGQR Systematics 89Y 124Sn 209Bi Pitthan 1980

  20. Compton Scattering on 6Li

  21. World Data SetD(g,g)D • Lucas – Illinois (1994) Eg = 49, 69 MeV • Hornidge – SAL (2000) Eg = 85-105 MeV • Lundin – Lund (2003) Eg = 55, 66 MeV • Myers and Shonyozov (coming 2013) Illinois, GW, UK, Lund Eg = 58-115 MeV

  22. Lundin Lucas Lucas, Lundin Hornidge EFT Fits to Deuteron Data Griesshammer 2012

  23. Quasi-free Compton scattering • Kossert (03) • Elastic Compton scattering • data from Lucas (94), Hornidge (00), Lundin (03) an = 11.6  1.5 (stat)  0.6 (Baldin) an = 11.1  1.8 (stat)  0.4 (Baldin) 0.8 (theory) bn = 3.6 1.5 (stat)  0.6 (Baldin)  +1.1 –0.6 an = 12.5  1.8(stat) (syst)  1.1(model) bn = 4.1 1.8 (stat)  0.4 (Baldin)  (0.8 (theory)  +0.6 –1.1 bn = 2.7 1.8(stat) (syst) 1.1(model)  Hildebrandt 05  Griesshammer 12 Summary of Neutron Results an = 12.6  1.5(stat)  2.0(syst) • Neutron scattering • Schmiedmayer (91)

  24. Experiment on 6Li at HIGS • experiment motivation • exploit higher nuclear cross section to measure a and b • cross section scales as Z2, so factor of 9x higher than 2H • solid 6Li target is simple • provided by Univ. of Saskatchewan • no previous Compton data on 6Li exists(except Pugh 1957) • energies: Eg = 60, 86 MeV • angles: qg = 40°-160° (Dq = 17°) • target: solid 12.7 cm long 6Li cylinder (plus empty) • detectors: eight 10”12” NaI’s (HINDA array) • good photon energy resolution (DEg/Eg < 5%)

  25. HINDA Array HIGS NaIDetector Array

  26. Experimental Setup

  27. Sample Spectra Full and Empty Targets Full  Empty subtraction 6Li(g,g)6Li Eg = 60 MeV

  28. Cross Section for 16O(g,g)16O

  29. Cross Section for 6Li(g,g)6Li L. Myers et al. Phys. Rev. C86 (2012) Eg = 60 MeV sum rule: a+b= 14.5

  30. Eg = 80 MeV 7.4% 12.8% Eg = 60 MeV Eg = 100 MeV (a, b) = (10.9, 3.6) 20.9% Da=2 Db= 2  sum rule: a+b= 14.5

  31. Cross Section for 6Li(g,g)6Li Eg = 86 MeV preliminary

  32. D(g,g)D Lundin (Lund) – 55 MeV Lucas (Illinois) – 49 MeV LIT Method for Compton Scattering Bampa 2011

  33. Nuclear Polarizabilityof 6Li (and 4He?)

  34. Nuclear Polarizability • nuclear polarizability affects energy levels of light atoms • non-negligible corrections for high-precision tests of QED • extraction of nuclear quantities from atomic spectroscopy • nuclear charge radius from Lamb shift in muonic atoms • usually determined from photoabsorption sum rule

  35. aE = 0.163  0.064 bM = 0.018  0.012 Nuclear Polarizability of 6Li

  36. q = 55 f = 90 q = 125 f = 90 6Li(g,g)6Li Eg = 3.0 MeV q = 55 f = 0 q = 125 f = 0

  37. q = 55 f = 90 q = 125 f = 90 6Li(g,g)6Li Eg = 4.2 MeV q = 55 f = 0 q = 125 f = 0

  38. Compton Scattering on the Proton and Deuteron

  39. Compton Scattering on Deuterium • unpolarized photon beam and unpolarized deuterium target • first use of our new LD2 cryogenic target • scattering angles 45o, 80o, 115o, 150o (Eg = 65, 100 MeV) • requires 300 hrs (65 MeV) + 100 hrs (100 MeV) • detectors: eight10”12” NaI’s (HINDA array) • arranged symmetrically left/right

  40. Cryogenic Target LH2/LD2/LHe (3.5K  24 K) • paid by GWU and TUNL • procured from vendors • assembled at HIGS • first run Oct. 2013?

  41. HINDA Array HIGS NaIDetector Array 55o 55o 125o 125o

  42. Sum-Rule-Independent Measurement of ap • linearly polarized photon beam (unpolarized target) • scintillating active target (detect recoils in coincidence) • measure scattered photons at 90o(Eg = 82 MeV) • scattering cross section is independent of bp • extraction of ap is independent of the Baldin sum rule • extraction of ap is model-independent • requires 300 hrs for 5% uncertainty in ap • detectors: four 10”12” NaI’s (HINDA array) • located left, right, up, down

  43. (point) (point) Sum-Rule-Independent Measurement of ap

  44. Polarizability of the Proton

  45. Scintillating Target simulations: R. Miskimen

  46. forward and backward spin polarizabilities Nucleon Spin Polarizability

  47. Polarization Observables Circular polarization RCP (+) Circular polarization LCP () Linear polarization

  48. Spin Polarizabilities of the Proton • measure S2x for first determination of proton gE1E1 • circularly polarized photon beam • scintillating active transversepolarized target (P ~ 80%) • scattering angles 65o, 90o, 115o (Eg = 100 MeV) • requires 800 hrs for DgE1E1 = 1 • detectors: eight10”12” NaI’s • 4 in plane, 4 out of plane Circular polarization

  49. Spin Polarizabilities of the Proton expand simulations: R. Miskimen

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