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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
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
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






Compton scattering at higs with polarized photons

TUNL

HIGS

TUNL

Triangle Universities Nuclear Laboratory



Compton scattering at higs with polarized photons

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


Compton scattering at higs with polarized photons

HIGS Photon Beam

to target room


Compton scattering at higs with polarized photons

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


Polarized compton scattering for ivgqr systematics
Polarized Compton Scatteringfor IVGQR Systematics


Compton scattering at higs with polarized photons

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


Compton scattering at higs with polarized photons

Photon Asymmetry in IVGQR

E1/E2 interference

pure E1


Compton scattering at higs with polarized photons

HINDA Array

HIGS NaI Detector Array

55o

55o

125o

125o


Compton scattering at higs with polarized photons

209Bi

Results for 209Bi


Compton scattering at higs with polarized photons

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



Compton scattering at higs with polarized photons

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


Compton scattering at higs with polarized photons

Lundin

Lucas

Lucas, Lundin

Hornidge

EFT Fits to Deuteron Data

Griesshammer 2012


Summary of neutron results

  • 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%)


Compton scattering at higs with polarized photons

HINDA Array

HIGS NaIDetector Array



Compton scattering at higs with polarized photons

Sample Spectra

Full and Empty Targets

Full  Empty subtraction

6Li(g,g)6Li

Eg = 60 MeV


Compton scattering at higs with polarized photons

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


Compton scattering at higs with polarized photons

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

L. Myers et al.

Phys. Rev. C86

(2012)

Eg = 60 MeV

sum rule: a+b= 14.5


Compton scattering at higs with polarized photons

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


Compton scattering at higs with polarized photons

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

Eg = 86 MeV

preliminary


Compton scattering at higs with polarized photons

D(g,g)D

Lundin (Lund) – 55 MeV

Lucas (Illinois) – 49 MeV

LIT Method for Compton Scattering

Bampa 2011


Nuclear polarizability of 6 li and 4 he
Nuclear Polarizabilityof 6Li (and 4He?)


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


Compton scattering at higs with polarized photons

aE = 0.163  0.064

bM = 0.018  0.012

Nuclear Polarizability of 6Li


Compton scattering at higs with polarized photons

q = 55 f = 90

q = 125 f = 90

6Li(g,g)6Li

Eg = 3.0 MeV

q = 55 f = 0

q = 125 f = 0


Compton scattering at higs with polarized photons

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 the proton and deuteron
Compton Scattering on the Proton and Deuteron


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


Compton scattering at higs with polarized photons

Cryogenic Target

LH2/LD2/LHe

(3.5K  24 K)

  • paid by GWU and TUNL

  • procured from vendors

  • assembled at HIGS

  • first run Oct. 2013?


Compton scattering at higs with polarized photons

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


Sum rule independent measurement of a p1

(point)

(point)

Sum-Rule-Independent Measurement of ap



Compton scattering at higs with polarized photons

Scintillating Target

simulations: R. Miskimen


Nucleon spin polarizability

forward and backward spin polarizabilities

Nucleon Spin Polarizability


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…




Cross section ratios for deuterium

DbN=1

Cross-Section Ratios for Deuterium




Compton scattering at higs with polarized photons

Calculations by Trento Group

  • photoabsorption on 6Li

    • Lorentz Integral Transform method

    • extend calculations to case of Compton scattering

Bacca 2002


Compton scattering at higs with polarized photons

NaI Detectors

Paraffin n shield

10" 10" NaI core detector

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

Pb collimator


Compton scattering at higs with polarized photons

q = 55

q = 125

Eg = 3.0 MeV

q = 55

q = 125

Eg = 4.2 MeV


Compton scattering at higs with polarized photons

Nuclear Polarizability of 4He

aE = 0.061  0.007 (stat)

 0.020 (syst)

bM = 0.007  0.001 (stat)

 0.002 (syst)


Compton scattering at higs with polarized photons

Nuclear Polarizability of 4He

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

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


Compton scattering at higs with polarized photons

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