Linear Linear PolarizationPolarization PropertiesProperties of Radiative Electron of Radiative Electron Capture Capture RevealedRevealed forfor RelativisticRelativistic ProjectilesProjectiles

Thomas Stöhlker

Gesellschaft für Schwerionenforschung (GSI)/Darmstadt and University of Frankfurt

ExperimentD. Banas, H.F. Beyer, F. Bosch, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Reuschl, D. Sierpowski, X. Ma, U. Spillmann, J. Rzadkiewicz, S. Tashenov and the ESR-Team

Atomic Physics Group, GSI-Darmstadt, GermanyIMP, Lanzhou, ChinaUniversity of Cracow, PolandUniversity of Frankfurt, Germany

in collaboration with

TheoryJ. Eichler, S. Fritzsche, A. Ichihara, T. Shirai, A. Surzhykov

Theoretische Physik, HMI-Berlin, GermanyJAERI, JapanUniversity of Kassel, Germany

Photoeffect, Radiative Electron Capture, and Polarization

Relativistic Quantum Dynamics

Polarization Studies of Radiative Capture Transitions: ExperimentA Diagnostic Tool to Identify Spin-Polarized Ion Beams

Detector Developments

Towards Polarization Studies of Inner Shell Transitions in Heavy Ions

Summary and Outlook

MotivationMotivationPolarization Studies for Hard X-Rays

Relativistic Particle Dynamcis(free-bound and free-free transitions):Synchrotron Radiation, Inverse Compton scattering Bremsstrahlung, and Recombination are the main photon processes in plasmas with distinct photon polarization features• Diagnostic tool to indentify spin polarized particle beams• Diagnostic tool to identify Thomson scattered photons from

laser produced relativistic electron bunches

Atomic Structure(bound-bound transitions): Excited states in heavy ions formed in atomic collisions areusually strongly aligned which translates in a polarization of theemitted photons

Radiative Recombination (RR) / Electron Capture (REC)

EKIN

ωh

electroncontinuum

bound states

• Electron capture into a bound ionic state by emission of a photon

• Time-reversed photionization

• Only possible capture/recombination process for bare ions colliding with electrons

KINEEω B +=h

8E L

E K

E KIN

Photoionization Radiative Electron Capture

hω

e-

e-hω

Relativistic Quantum Dynamics

Experiments at the Jet-Target

Stored Ions (Z=Q)

Dipole Magnet

Gas Jet

EKIN

ωhK

L

K-REC

∞

Electron transfer fromthe targetatom into theHCI

...ωZeZ

1)(Q

Q

++→

++−

−+

h

Particle Counter(MWPC)

Ge Detector

50 100 150 200 250 300 350

0

200

400

Lyα1 K-R

EC

8-RE

C

M-R

EC L-R

EC

Lyβ

Lyα2

Ere

igni

sse

Photonenenergie (keV)

Coincidence

Experimental REC Studies

0 .01

0 .1

1

10

100

1000

1 10 100

ad iaba tis ity pa ram eter η

cros

s se

ctio

n pe

r tar

get e

lect

ron

σ(ba

rn)

0 .1 1 10 beam ene rgy [G eV /u ] (fo r A u 79+ ions)

0 .01

0 .1

1

10

100

1000

1 10 100

ad iaba tis ity pa ram eter η

cros

s se

ctio

n pe

r tar

get e

lect

ron

σ(ba

rn)

0 .1 1 10 beam ene rgy [G eV /u ] (fo r A u 79+ ions)

complete relativistic calculationsfor Au 79+ (Eichler et. al)dipole approximation

K

KIN

EEη =

Total REC cross sections for bare ionsup to uranium (20 MeV/u – 170 GeV/u)

K

∞

ωh

Ekin

0 20 40 60 80 100 120 140 160 1800

1

2

3

4

5

6

7

complete relativistic calculations (Eichler et al.)nonrelativistic dipole distribution

dσ/dΩ

[arb

itrar

y un

its]

magnetic transitions

observation angle θ [deg]

laboratory frameU92+=>N2, 309.7 MeV/u

photon angular distributionstudies for REC

Kinematical Identification of Spin-FlipTransitions from Continuum States into

the 1s-Ground State

Photon PolarizationPhoton Polarization

E

B

e- Electron is ejectedalong the electric field

Nonrelativistic dipoleapproximation

E

B

e-

E

B

e- Electron is ejectedalong the electric field

Nonrelativistic dipoleapproximation

Photoionizationnon-relativistic dipole approximation: 100 % polarization for all emission angles

e-

E

Radiative Electron Capture

KK--REC Photon PolarizationREC Photon Polarization

0 30 60 90 120 150 180-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

1.25

degr

ee o

f lin

ear p

olar

izat

ion

angle θ (deg)0 30 60 90 120 150 180

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

1.25

300 MeV 500 MeV 800 MeV

degr

ee o

f lin

ear p

olar

izat

ion

angle θ (deg)

K-REC into bare uranium ions(U92+ + e- ⇒ U91+ + ħω )

non-relativisticdipole approximation:100 % polarizationfor all emission angles

large relativistic contributions

Eichler et al., PRA, 2001Surzykov et al., PRA, 2001

Energy and Charge DependenceEnergy and Charge Dependence

0 30 60 90 120 150 1800.0

0.2

0.4

0.6

0.8

1.0

degr

ee o

f lin

ear p

olar

izat

ion

angle θ (deg)

100 MeV/u 300 MeV/u 500 MeV/u

Argon (Z=18)

0 30 60 90 120 150 180-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

20 MeV/u 100 MeV/u 300 MeV/u 500 MeV/u 800 MeV/u

degr

ee o

f lin

ear p

olar

izat

ion

angle θ (deg)

Uranium (Z=92)

10-1 100 101 102 103 104 105 106 107

energy (eV)

Micropattern gascounters

CCD cameras

x-ray optics

Photon Polarimetry

Bragg reflection

Photoabsorption

Thomson scatteringCompton scattering

Wollaston prism

Crystal optics

Lyquid crystals

LCD

Segmented solidstate detectors

2D Position Sensitive Ge(i) Detectors

MicroMicro--Strip Germanium Detector Development:Strip Germanium Detector Development:

Energy Resolved X-Ray Imager, Timing, Multi-Hit Capability

• precision spectroscopy• Doppler tuned spectroscopy• atomic lifetime studies

• polarization studies• Compton cameras• x-ray îmager

e.g. medical applications

Interaction of electro-magnetic radiationwith matter

- photoelectric effect

- Compton scattering

- pair production100 101 102 103 104 105

10-4

10-3

10-2

10-1

100

101

102

103

104

atte

nuat

ion

1/cm

energy (KeV)

Photabsorption

ComptonPair Production

TotalK

L

Germanium

Compton Scattering

0 30 60 90 120 150 1800

50

100

150

150 keV

phot

on e

nerg

y (k

eV)

scattering angle0 30 60 90 120 150 180

0

50

100

150

200

250

250 keV

phot

on e

nerg

y (k

eV)

scattering angle

hωe-

θc

)cos1(1'

2 celcm

θωωω−+

=h

hh

Polarization Measurementby Means of Compton scattering

Klein-Nishina equation

)cos θsin2'

'()'(21 2222

0 ϕωω

ωω

ωωσ

−+=Ω h

h

h

h

h

hrdd

hω

hω ´θ

ϕ

E

0

30

60

90

120

150

180

210

240

270

300

330

ϕ

E

Pixel Detector -Coincidence Technique

hω

coincidence

hω′∆Eel

E= hωE= ∆Εel + hω′50 100 150 200 250 300

0

5000

10000

15000

20000

25000

Lyβ

energy (KeV)

Lyα

K-R

EC

L-R

EC

M-,

N-..

REC

single pixel spectrum

50 100 150 200 250 300048

12

energy (KeV)

50 100 150 200 250 300048

12recoil electron

Compton photon

50 100 150 200 250 3000

1000

2000

3000

4000K-REC

L-RECM,..-REC

energy (KeV)

coincident sum spectrum

4 x 7 mm 15 m

m

4 x

7 m

m

Preliminary

Compton Kinematics

180 160 140 120 100 80 60 40 20 0

0

20

40

60

80

100

120

140

160

180

200

220

240

260

ener

gy (k

eV)

scattering angle (θ)180 160 140 120 100 80 60 40 20 0

0

50

100

150

200

250

300

350

400

ener

gy (k

eV)

scattering angle (θ)

)cos1(1'

2 celcm

θωωω−+

=h

hhhω

e-

θc

keV 240ω=h keV 350ω=h

Compton photon

Recoil electron

ℏω'

Preliminary

Polarization Experiment (U92+ + e- ⇒ U91+ + ħω )

gas

ta

rget

ion beam (400 MeV/u)

EKIN

ωhK

L

K-REC

∞

hω

E

hω´

⊥I

6000 6500 7000 7500 80000

3

6

9

coun

ts (a

rb. u

nits

)

energy (channels)

I⊥ (∆E+hω´)

∆E hω´||I

6000 6500 7000 7500 80000

3

6

9

coun

ts (a

rb. u

nits

)

energy (channels)

I⊥ (∆E+hω´)I(∆E+hω´)

Preliminary

K-REC radiation isstrongly polarized

polarization iswithin the scattering plane

Experiment

Polarization Measurement for RadiativeRecombination Transitions (U92+ + e- ⇒ U91+ + ħω )

0

30

60

90

120

150

180

210

240

270

300

330

ion beam (400 MeV/u)

targ

etga

s

K-REC

hω

E

GSI ESR Storage Ring

Preliminary

Preliminary Results

0 30 60 90 120 150 180-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

100 MeV/u 400 MeV/u 800 MeV/u

degr

ee o

f the

line

ar p

olar

isat

ion

observation angle θlab(deg)

Angular dependence

50 100 150 200 250 300 350 400 450 500 5500.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

degr

ee o

f the

line

ar p

olar

izat

ion

projectile energy (MeV/u)

Energy dependence

θ=60o

Experiment: Tachenov et al., PHD Thesis 2005

Exact Relativistic Treatment Eichler et al., PRA, 2001Surzykov et al., PRA, 2001

Preliminary

Crossover PhenomenonCrossover Phenomenon

0 30 60 90 120 150 180-0,50

-0,25

0,00

0,25

0,50

0,75

1,00

300 MeV 500 MeV 800 MeV

degr

ee o

f lin

ear p

olar

izat

ion

angle θ (deg)

E

B

e- Electron is ejectedalong the electric field

Nonrelativistic dipoleapproximation

E

B

e-

E

B

e-Electron is ejected

along the magnetic field

e-

e-

along the electric field

K-REC polarizationPhotoionization

]Bv[EF ×+∝

Ion Beam Spin PolarizationIon Beam Spin Polarizationfor spin polarized particles, the Stokes parameter P2is non-zero => polarization plane and scattering plane are not equal

Ψion beam

E

S

0 30 60 90 120 150 180-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Stokes Parameters P1

P2

degr

ee o

f lin

ear p

olar

izat

ion

angle θ (deg)

Uranium 500 MeV/u

1

22tan PP=Ψ

ψ degree of ion beamspin polarization⇒

A.Surzhykov, Kassel Uni

900

9001 II

IIP +−=

13545

135452 II

IIP +−=

Detection of spin polarized ion beams

gas

ta

rget

ion beam

hω

unpolarized ion beamsspin polarized ion beams

EKIN

ωhK

L

K-REC

∞

A.Surzhykov et al., PRL 94, 203202 (2005)

0

30

60

90

120

150

180

210

240

270

300

330

0

30

60

90

120

150

180

210

240

270

300

330

Energy Resolution Position Resolution (2D/3D)

Timing

ESRFESRF

at ESRF: systematic studies of the detector responce for the 2Dpolarimeter (e.g. polarization sensitivity)

50 keV to 500 keV

Detector

LN2-Dewar128+48 preamplifier

Photons

∅ 360 mm

~700 mm

2D 2D µµstripstrip detectordetector systemsystem

Front: 128 strips pitch ~250µm

Back: 48 strips pitch ~1167µm

Crystal sizeheigth: 32 mmwidth: 56 mmthickness: 11 mm

X

Y

E1 (X1)

E1 (Y1)

E2 (X2)E2 (Y2)

E2(X2,Y2)

E1(X1,Y1)

Strip Strip DetectorDetector: Analysis of : Analysis of ComptonCompton EventsEvents=> => UseUse Multihit Multihit SensitivitySensitivityhω

a) Double Hits on Front Sideb) Double Hits on Back Sidec) Compare Energy Informationto fix (X1,Y1) and (X2,Y2)

180 160 140 120 100 80 60 40 20 0

020406080

100120140160180200220

ener

gy (k

eV)

scattering angle

scattered photon recoil electron

hωe-

θc

hω′

2D images of the Compton scattering distribution in germanium as function of the scattering angle The data were recored at the ESRF using 98% linearlypolarized photons with en energy of 210 keV.

angulardistributionof theComptonscatteredphotons

Preliminary

Compton Imager and Polarimeterfor Hard X-Rays @ ESR

Polarization Spectroscopy of Photon-Matter Interaction

Preliminary

2D images of the Compton scattering distribution in germaniumas function of the scattering angle The data were recored at the ESRF using 98% linearly polarizedphotons with an energy of 210 keV.

What About Inner Shell Transitions with EnergiesBelow 100 keV ?

0 30 60 90 120 150 180

0.30

0.35

0.40

0.45

0.50

0.55

βA = -0.225 ± 0.017

Rat

io L

yα1/L

yα2

observation angle θ [deg]

1 10 100 1000 10000 1000001E-4

1E-3

0,01

0,1

1

10

100

1000

10000

atte

nuat

ion

(1/c

m)

energy (KeV)

Photabsorption

Compton

Pair Production

Total

K

L150 keV

Germanium

bound-free, free-free transitions

1 10 100 1000 10000 1000001E-4

1E-3

0,01

0,1

1

10

100

1000

10000

K

energy (KeV)

atte

nuat

ion

(1/c

m)

Photabsorption

Compton

Pair Production

Total

56 keV

Silicon

bound-bound transitions

2p3/2 transitionsin high-Z ions

populated by electroncapture

2p3/2 Transitions in High-Z Ions Produced by REC

145 150 155 160 165 170 175 180 185

0

200

400

coun

ts

photon energy [keV]

Lyα22p1/2+2s1/2

1s1/2

2p3/2

elec

tron

capt

ure

E1

µ=+3/2µ=+1/2µ=-1/2µ=-3/2

Lyα12p3/2

0 30 60 90 120 150 180

0.30

0.35

0.40

0.45

0.50

0.55

βA = -0.225 ± 0.017

Rat

io L

yα1/L

yα2

observation angle θ [deg]

Lyα1 transitions

( ) ⎥⎦⎤

⎢⎣⎡ −•+∝ θsin

231β1θW 2

A

Strong AlignmentPRL 79, 3270 (1997)Multipolmixing E1/M2 PRL 88 153001 (2002)

M2 (1%)

HeliumHelium--likelike UraniumUranium::ParityParity ViolationViolation in Heavy Ionsin Heavy Ions

( )1 1 2 1 vE M E p+

( )10 1 ,2S s s ( )3

0 1 ,2P s p

( )31 1 ,2S s s

( )10 1 ,1S s s

2 1E

1010 sτ −≈1310 sτ −≈

( )10 165114.406 eVE S = −

( )30 165113.5 eVE P = −

0.906 eVE∆ = −

Parityadmixture

65 10η −= ⋅

200 400 600 800 1000 1200 1400 1600

100

200

300

400

500

600

700

800

900

2E1

M1

coun

ts

energy (channels)

Check for the Asymmetry in the Linearor Circular Polarization of the 2E1Transitions

gas

ta

rget

ion beam

hω

EKIN

ωh

K

L

K-REC

∞Summary and Outlook

• segmented solid state detectors an excellent tool for polarization studies in the hard X-Ray regime

• for REC: first polarization studies for hard x-rays

• diagnostic tool for spin polarized ion beams

• using Si(Li) strip detectors, such studies can be extended to inner-shell transitions

• towards a study of parity violation experiments in atomic systems at high-Z

• further sensitivity enhancement via 3D readout

• a lots of applications