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

Outline What (and where) is HIGS?  What (and where) is HIGS? What have we done so far at HIGS?  What have we done so far at HIGS?  polarized Compton scattering study of IVGQR  elastic Compton scattering on 6 Li high energy (60-86 MeV) and low energy (3-5 MeV) What are we planning to do at HIGS?  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

Background Information on HIGS

United States

North Carolina

Duke University

TUNL HIGS TUNL Triangle Universities Nuclear Laboratory

Duke Free-Electron Laser Lab

Storage Ring and Booster Circularly and linearly polarized  rays, nearly monoenergetic (E   2 – 90 MeV) Utilizes Compton backscattering to generate  rays Booster Injector LINAC RF Cavity Mirror Optical Klystron FEL

HIGS Photon Beam to target room

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  ~10 7 Hz at MeV  ~10 8 Hz below 15 MeV  low beam-related background  no bremsstrahlung typical of tagged photons

Polarized Compton Scattering for IVGQR Systematics

Giant Resonances L = 1 L = 2 T = 0T = 1  collective nuclear excitations  GDR and ISGQR well known IVGQR poorly known  IVGQR poorly known isovector  photon as isovector probe use pol. photons for IVGQR  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 ratio of H/V scattered photons is sensitive to E1/E2 interference sign difference in interference term at forward/backward angles sign difference in interference term at forward/backward angles

Photon Asymmetry in IVGQR pure E1 E1/E2 interference

HINDA Array HINDA HIGS NaI Detector Array 55 o 125 o

209 Bi Results for 209 Bi

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

Results for 124 Sn

IVGQR Systematics 89 Y 209 Bi Pitthan Sn

Compton Scattering on 6 Li

World Data Set D(,)D  Lucas – Illinois (1994) E  = 49, 69 MeV  Hornidge – SAL (2000) E  = MeV  Lundin – Lund (2003) E  = 55, 66 MeV  Myers and Shonyozov (coming 2013) (coming 2013) Illinois, GW, UK, Lund E  = MeV

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

Summary of Neutron Results  Neutron scattering  Schmiedmayer (91)  n = 12.6  1.5(stat)  2.0(syst)  Quasi-free Compton scattering  Kossert (03)  n = 12.5  1.8(stat)(syst)  1.1(model) +1.1 –0.6  n = (stat) (syst) 1.1(model) +0.6 –1.1    Elastic Compton scattering  data from Lucas (94), Hornidge (00), Lundin (03)  n = 11.6  1.5 (stat)  0.6 (Baldin)  n = (stat)  0.6 (Baldin)  Hildebrandt 05  n = 11.1  1.8 (stat)  0.4 (Baldin)  0.8 (theory)  n = (stat)  0.4 (Baldin)  (0.8 (theory)  Griesshammer 12

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

HINDA Array HINDA HIGS NaI Detector Array

Experimental Setup

Sample Spectra 6 Li( ,  ) 6 Li E  = 60 MeV Full and Empty Targets Full  Empty subtraction

Cross Section for 16 O(,) 16 O

Cross Section for 6 Li(,) 6 Li sum rule:   +  = 14.5 L. Myers et al. Phys. Rev. C86 (2012) E  = 60 MeV

(, ) = (10.9, 3.6)  = 2  = 2  sum rule:   +  = 14.5 E  = 60 MeV  7.4% E  = 80 MeV  12.8% E  = 100 MeV  20.9%

E  = 86 MeV Cross Section for 6 Li(,) 6 Li preliminary

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

Nuclear Polarizability of 6 Li (and 4 He?)

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

Nuclear Polarizability of 6 Li  E =   M =  0.012

E  = 3.0 MeV 6 Li( ,  ) 6 Li  = 55   = 90   = 55   = 0   = 125   = 0   = 125   = 90 

E  = 4.2 MeV 6 Li( ,  ) 6 Li  = 55   = 90   = 55   = 0   = 125   = 0   = 125   = 90 

Compton Scattering on the Proton and Deuteron

Compton Scattering on Deuterium  unpolarized photon beam and unpolarized deuterium target  first use of our new LD 2 cryogenic target  scattering angles 45 o, 80 o, 115 o, 150 o (E  = 65, 100 MeV)  requires 300 hrs (65 MeV) hrs (100 MeV)  detectors: eight 10”12” NaI’s (HINDA array)  arranged symmetrically left/right

LH 2 /LD 2 /LHe Cryogenic Target  paid by GWU and TUNL  procured from vendors  assembled at HIGS  first run Oct. 2013? (3.5 K  24 K)

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

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

Sum-Rule-Independent Measurement of  p (point)

Polarizability of the Proton

Scintillating Target simulations: R. Miskimen

Nucleon Spin Polarizability forward and backward spin polarizabilities

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

Spin Polarizabilities of the Proton first determination of proton  E1E1  measure  2x for first determination of proton  E1E1  circularly polarized photon beam transverse  scintillating active transverse polarized target (P ~ 80%)  scattering angles 65 o, 90 o, 115 o (E  = 100 MeV)  requires 800 hrs for  E1E1 = 1  detectors: eight 10”12” NaI’s  4 in plane, 4 out of plane Circular polarization

Spin Polarizabilities of the Proton expand simulations: R. Miskimen

Summary Early measurements of Compton scattering at HIGS  Early measurements of Compton scattering at HIGS  polarized A(,)A for A = (IVGQR systematics)  6 Li(,) 6 Li at 60, 86 MeV (nucleon polarizability)  polarized 6 Li(,) 6 Li at MeV (nuclear polarizability) Next generation of experiments on light nuclei  Next generation of experiments on light nuclei  D(,)D at 65 and 100 MeV (neutron polarizability) polarized  polarized p(,)p at 82 MeV (proton electric polarizability) polarized  polarized 4 He(,) 4 He at 3-15 MeV (nuclear polarizability) double-polarized  double-polarized Compton scattering on proton/deuteron nucleon spin polarizability HIGS can contribute high-quality polarized data!  HIGS can contribute high-quality polarized data!  stay tuned for further developments in the future…

Extra slides

Phenomenological Formalism

Cross-Section Ratios for Deuterium  N = 1

Level Scheme of 6 Li

Nuclear Polarizability

Calculations by Trento Group Bacca 2002  photoabsorption on 6 Li Lorentz Integral Transform method extend calculations to case of Compton scattering

NaI Detectors Pb collimator Paraffin n shield 10"  10" NaI core detector 3" thick optically isolated NaI shield segments (8 in total)

E  = 3.0 MeV E  = 4.2 MeV  = 55   = 125 

Nuclear Polarizability of 4 He  E =  (stat)  (syst)  M =  (stat)  (syst)

Nuclear Polarizability of 4 He  E =  (stat)  (syst)  M =  (stat)  (syst)

Compton Scattering with scintillating target Light Output Missing Energy (MeV) deuteronproton simulations: R. Miskimen

Nucleon Spin Polarizability  classical analogy: Faraday rotation of linearly polarized light in a spin-polarized medium  four spin polarizabilities:  1, …, 4  forward spin polarizability:  0 =  1 –  2 – 2 4  backward spin polarizability:   =  1 +  2 + 2 4  expt. asymmetries with circularly polarized photons   x : target spin  photon helicity (in reaction plane)   z : target spin parallel to photon helicity