Compton Scattering at HIGS Compton Scattering at HIGS

with Polarized Photonswith Polarized Photons

George Washington UniversityGeorge Washington University Jerry FeldmanJerry Feldman Mark SikoraMark Sikora

Duke University/TUNL Luke Myers Luke Myers Henry Weller Mohammad Ahmed Jonathan Mueller Seth Henshaw

Compton@HIGS CollaborationCompton@HIGS 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 6Li 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 Background

Information on Information on

HIGSHIGS

United States

North Carolina

Duke University

TUNLHIGSHIGS

TUNLTUNLTriangle Universities Nuclear Laboratory

Duke Free-Electron Laser Lab

Storage Ring and Booster

Circularly and linearly polarized Circularly and linearly polarized rays, nearly rays, nearly monoenergeticmonoenergetic ( (EE 2 2––90 MeV) 90 MeV)

Utilizes Compton backscattering to generate Utilizes Compton backscattering to generate raysrays

Booster InjectorBooster Injector

LINACLINAC

RF CavityRF Cavity

MirrorMirror

Optical KlystronOptical Klystron

FELFEL

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 ScatteringPolarized Compton Scattering

for IVGQR Systematicsfor IVGQR Systematics

Giant Resonances

L = 1

L = 2

T = 0 T = 1 collective nuclear excitations

GDR and ISGQR well known

IVGQR poorly knownIVGQR poorly known

photon as isovectorisovector probe

use pol. photons for IVGQRuse 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 ratio of H/V scattered photons is sensitive to E1/E2 interferenceE1/E2 interference

• sign difference in interference term at forward/backward anglessign difference in interference term at forward/backward angles

Photon Asymmetry in IVGQR

pure E1 E1/E2 interference

HINDA Array HIHIGS NNaI DDetector AArray

55o 55o

125o

125o

209Bi

Results for 209Bi

Results for 89Y

measured measured 124124Sn last month!Sn last month!

lease 142Nd target from ORNL for $15k

other targets include A ~ 56, 180, 238

extend measurements to extend measurements to 8989YY

%18%110

88.123.8

2.07.270

S

E

EWSR

MeV

MeV

89Y

preliminary

Results for 124Sn

IVGQR Systematics

89Y

209Bi

Pitthan 1980

124Sn

Compton Scattering Compton Scattering

on on 66LiLi

World Data Set

D(,)D

Lucas – Illinois (1994)Lucas – Illinois (1994)EE = 49, 69 MeV = 49, 69 MeV

Hornidge – SAL (2000)Hornidge – SAL (2000)EE = 85-105 MeV = 85-105 MeV

Lundin – Lund (2003)Lundin – Lund (2003)EE = 55, 66 MeV = 55, 66 MeV

Myers and ShonyozovMyers and Shonyozov (coming 2013)(coming 2013)Illinois, GW, UK, LundIllinois, GW, UK, Lund

EE = 58-115 MeV = 58-115 MeV

EFT Fits to Deuteron Data

LundinLundinLucasLucas

Lucas, LundinLucas, Lundin HornidgeHornidge

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 = 2.7 1.8(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 = 3.6 1.5 (stat) 0.6 (Baldin)

Hildebrandt 05

n = 11.1 1.8 (stat) 0.4 (Baldin) 0.8 (theory)n = 4.1 1.8 (stat) 0.4 (Baldin) (0.8 (theory)

Griesshammer 12

Experiment on 6Li at HIGS

energies: EE = 60, 86 MeV = 60, 86 MeV

angles: = 40°-160° = 40°-160° ( = 17°)

target: solid 12.7 cm long 12.7 cm long 66LiLi cylinder (plus empty)

detectors: eight 10”eight 10”12” NaI’s12” 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 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)

HINDA Array HIHIGS NNaI DDetector AArray

Experimental Setup

Sample Spectra

6Li(,)6Li E = 60 MeV

Full and Empty Targets Full Empty subtraction

Cross Section for 16O(,)16O

Cross Section for 6Li(,)6Li

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

EE = 60 MeV = 60 MeV

7.4%

EE = 80 MeV = 80 MeV

12.8%

EE = 100 MeV = 100 MeV

20.9%

E = 86 MeV

Cross Section for 6Li(,)6Li

preliminary

Bampa 2011

Lundin (Lund) – 55 MeVLucas (Illinois) – 49 MeVLucas (Illinois) – 49 MeV

D(D(,,)D)D

LIT Method for Compton Scattering

Nuclear Polarizability Nuclear Polarizability

of of 66Li (and Li (and 44He?)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 6Li

E = 0.163 0.064

M = 0.018 0.012

E = 3.0 MeV

6Li(,)6Li

= 55 = 90

= 55 = 0 = 125 = 0

= 125 = 90

E = 4.2 MeV

6Li(,)6Li

= 55 = 90

= 55 = 0 = 125 = 0

= 125 = 90

Compton ScatteringCompton Scattering

on the on the

Proton and DeuteronProton and Deuteron

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 (E = 65, 100 MeV)

requires 300 hrs (65 MeV) + 100 hrs (100 MeV)

detectors: eight 10”12” NaI’s (HINDA array) arranged symmetrically left/right

LHLH22/LD/LD

22/LHe/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 HIHIGS NNaI DDetector AArray

55o

125o

55o

125o

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 90measure scattered photons at 90oo (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)

(point)

Polarizability of the Proton

Scintillating Target

simulations: R. Miskimen

Nucleon Spin Polarizability

forward and backward spin polarizabilities

Polarization Observables

xy

z

k

k

d

RCP (+)

LCP ()

Circular polarization

Circular polarization

Linear polarization

z2

x2

||

||

3

Spin Polarizabilities of the Proton

measure 2x for first determination of proton first determination of proton E1E1E1E1

circularly polarized photon beam scintillating active transversetransverse polarized target (P ~ 80%)

scattering angles 65o, 90o, 115o (E = 100 MeV)

requires 800 hrs for E1E1 = 1

detectors: eight 10”12” NaI’s 4 in plane, 4 out of plane

Circular polarization

x2

Spin Polarizabilities of the Proton

expandexpand

simulations: R. Miskimen

Summary

Early measurements of Compton scattering at HIGSEarly measurements of Compton scattering at HIGS polarized A(,)A for A = 89-209 (IVGQR systematics)

6Li(,)6Li at 60, 86 MeV (nucleon polarizability)

polarized 6Li(,)6Li at 3.0-4.2 MeV (nuclear polarizability)

Next generation of experiments on light nucleiNext generation of experiments on light nuclei D(,)D at 65 and 100 MeV (neutron polarizability)

polarizedpolarized p(,)p at 82 MeV (proton electric polarizability)

polarizedpolarized 4He(,)4He at 3-15 MeV (nuclear polarizability)

double-polarizeddouble-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

,,,,, 21 ERERERERER SGSGQDGR

)(1)()()()(, 102211 EGREEEEGR gr

A

NZgEfgEfER

)()()(, 120 EQDQDQD gqFr

A

NZEfER

4

1

2

1

2

011 )()()(, EOgAc

EgA

c

EZrqFER ME

SG

QDGRSG r

A

NZqFER 022 )(,

Phenomenological Formalism

Cross-Section Ratios for Deuterium

N = 1

Level Scheme of 6Li

Nuclear Polarizability

Calculations by Trento Group

Bacca 2002

photoabsorption on 6Li• 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

= 55 = 125

= 125

Nuclear Polarizability of 4He

E = 0.061 0.007 (stat) 0.020 (syst)

M = 0.007 0.001 (stat) 0.002 (syst)

Nuclear Polarizability of 4He

E = 0.061 0.007 (stat) 0.020 (syst)

M = 0.007 0.001 (stat) 0.002 (syst)

Compton Scattering with scintillating targetLig

ht

Ou

tpu

t

Missing Energy (MeV)

deuteron proton

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 – 24

backward spin polarizability: = 1 + 2 + 24

expt. asymmetries with circularly polarized photons x : target spin photon helicity (in reaction plane)

z : target spin parallel to photon helicity