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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






TUNL

HIGS

TUNL

Triangle Universities Nuclear Laboratory



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


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

    • ~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


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


Photon Asymmetry in IVGQR

E1/E2 interference

pure E1


HINDA Array

HIGS NaI Detector Array

55o

55o

125o

125o


209Bi

Results for 209Bi


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



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


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%)


HINDA Array

HIGS NaIDetector Array



Sample Spectra

Full and Empty Targets

Full  Empty subtraction

6Li(g,g)6Li

Eg = 60 MeV


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


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

L. Myers et al.

Phys. Rev. C86

(2012)

Eg = 60 MeV

sum rule: a+b= 14.5


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


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

Eg = 86 MeV

preliminary


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


aE = 0.163  0.064

bM = 0.018  0.012

Nuclear Polarizability of 6Li


q = 55 f = 90

q = 125 f = 90

6Li(g,g)6Li

Eg = 3.0 MeV

q = 55 f = 0

q = 125 f = 0


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


Cryogenic Target

LH2/LD2/LHe

(3.5K  24 K)

  • paid by GWU and TUNL

  • procured from vendors

  • assembled at HIGS

  • first run Oct. 2013?


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



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




Calculations by Trento Group

  • photoabsorption on 6Li

    • Lorentz Integral Transform method

    • extend calculations to case of Compton scattering

Bacca 2002


NaI Detectors

Paraffin n shield

10" 10" NaI core detector

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

Pb collimator


q = 55

q = 125

Eg = 3.0 MeV

q = 55

q = 125

Eg = 4.2 MeV


Nuclear Polarizability of 4He

aE = 0.061  0.007 (stat)

 0.020 (syst)

bM = 0.007  0.001 (stat)

 0.002 (syst)


Nuclear Polarizability of 4He

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

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


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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