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Compton Scattering at HIGS with Polarized Photons. [email protected] 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
Compton Scattering at HIGS with Polarized Photons

[email protected] 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
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
slide7

TUNL

HIGS

TUNL

Triangle Universities Nuclear Laboratory

slide9

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

slide10

HIGS Photon Beam

to target room

slide11

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
slide13

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
slide14

Photon Asymmetry in IVGQR

E1/E2 interference

pure E1

slide15

HINDA Array

HIGS NaI Detector Array

55o

55o

125o

125o

slide16

209Bi

Results for 209Bi

slide17

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

slide19

IVGQR Systematics

89Y

124Sn

209Bi

Pitthan 1980

world data set d g g d
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

slide22

Lundin

Lucas

Lucas, Lundin

Hornidge

EFT Fits to Deuteron Data

Griesshammer 2012

summary of neutron results

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)
experiment on 6 li at higs
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%)
slide25

HINDA Array

HIGS NaIDetector Array

slide27

Sample Spectra

Full and Empty Targets

Full  Empty subtraction

6Li(g,g)6Li

Eg = 60 MeV

slide29

Cross Section for 6Li(g,g)6Li

L. Myers et al.

Phys. Rev. C86

(2012)

Eg = 60 MeV

sum rule: a+b= 14.5

slide30

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

slide31

Cross Section for 6Li(g,g)6Li

Eg = 86 MeV

preliminary

slide32

D(g,g)D

Lundin (Lund) – 55 MeV

Lucas (Illinois) – 49 MeV

LIT Method for Compton Scattering

Bampa 2011

nuclear polarizability
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
slide35

aE = 0.163  0.064

bM = 0.018  0.012

Nuclear Polarizability of 6Li

slide36

q = 55 f = 90

q = 125 f = 90

6Li(g,g)6Li

Eg = 3.0 MeV

q = 55 f = 0

q = 125 f = 0

slide37

q = 55 f = 90

q = 125 f = 90

6Li(g,g)6Li

Eg = 4.2 MeV

q = 55 f = 0

q = 125 f = 0

compton scattering on deuterium
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
slide40

Cryogenic Target

LH2/LD2/LHe

(3.5K  24 K)

  • paid by GWU and TUNL
  • procured from vendors
  • assembled at HIGS
  • first run Oct. 2013?
slide41

HINDA Array

HIGS NaIDetector Array

55o

55o

125o

125o

sum rule independent measurement of a p
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
slide45

Scintillating Target

simulations: R. Miskimen

polarization observables
Polarization Observables

Circular polarization

RCP (+)

Circular polarization

LCP ()

Linear polarization

spin polarizabilities of the proton
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

spin polarizabilities of the proton1
Spin Polarizabilities of the Proton

expand

simulations: R. Miskimen

summary
Summary
  • Early measurements of Compton scattering at HIGS
    • polarized A(g,g)A for A = 89-209 (IVGQR systematics)
    • 6Li(g,g)6Li at 60, 86 MeV (nucleon polarizability)
    • polarized 6Li(g,g)6Li at 3.0-4.2 MeV (nuclear polarizability)
  • Next generation of experiments on light nuclei
    • D(g,g)D at 65 and 100 MeV (neutron polarizability)
    • polarizedp(g,g)p at 82 MeV (proton electric polarizability)
    • polarized4He(g,g)4He at 3-15 MeV (nuclear polarizability)
    • double-polarized Compton scattering on proton/deuteron
      • nucleon spin polarizability
  • HIGS can contribute high-quality polarized data!
    • stay tuned for further developments in the future…
slide57

Calculations by Trento Group

  • photoabsorption on 6Li
    • Lorentz Integral Transform method
    • extend calculations to case of Compton scattering

Bacca 2002

slide58

NaI Detectors

Paraffin n shield

10" 10" NaI core detector

3" thick optically isolated NaI shield segments (8 in total)

Pb collimator

slide59

q = 55

q = 125

Eg = 3.0 MeV

q = 55

q = 125

Eg = 4.2 MeV

slide60

Nuclear Polarizability of 4He

aE = 0.061  0.007 (stat)

 0.020 (syst)

bM = 0.007  0.001 (stat)

 0.002 (syst)

slide61

Nuclear Polarizability of 4He

aE = 0.061  0.007 (stat)  0.020 (syst)

bM = 0.007  0.001 (stat)  0.002 (syst)

slide62

Compton Scattering with scintillating target

Light Output

Missing Energy (MeV)

deuteron

proton

simulations: R. Miskimen

nucleon spin polarizability1
Nucleon Spin Polarizability
  • classical analogy: Faraday rotation of linearly polarized light in a spin-polarized medium
  • four spin polarizabilities: g1, …,g4
    • forward spin polarizability: g0 = g1 – g2 – 2g4
    • backward spin polarizability: gp = g1 + g2 + 2g4
  • expt. asymmetries with circularly polarized photons
    • Sx : target spin  photon helicity (in reaction plane)
    • Sz : target spin parallel to photon helicity
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