linearly polarised photons and determining the ...€¦ · information provided by the photon...

Linearly polarised photons and determining thepolarisation degree

Simon Gardner

NSTAR2019Bonn

11th June 2019

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Motivation - N∗ programme

N∗ programme reliant on linear polarisation.

Beam Target Recoil Target + Recoilx ′ y ′ z ′ x ′ x ′ z ′ z ′

x y z x z x zUnpol σ0 T P Tx′ Lx′ Tz′ Lz′Linear Σ H P G Ox′ T Oz′Circular F E Cx′ Cz′

Motivation - Selection of Measurements

Experiment Reaction Obs Energy Syst Error Method YearYerevan pγ → pπ0 Σ 0.5→ 1.1GeV 3.2% ANB 2001Max III 12C(, p)11B Σ 40→ 50MeV 5% ANB 2016Clas pγ → pπ0 Σ 1.1→ 1.8GeV 4% Brems Fit 2013CBELSA pγ → pπ0 G 0.6→ 1.3GeV 2.7% ANB 2017A2 pγ → pπ0 Σ 320→ 650MeV 3% Brems Fit 2016GlueX pγ → pπ0 Σ 8.1→ 9.0GeV 1.5% Triplet Pol 2017

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Generation of Coherent Bremsstrahlung

γEγ =E0−E1

+

-E0

v0

-E1

v1

(MeV)γE100 200 300 400 500 600 700 800 900 1000

Inte

nsity

Generated using diamondradiator.Cover full range beam energy.Understood but complexpolarisation energy dependence.

Generation of Coherent Bremsstrahlung

γEγ =E0−E1

+

-E0

v0

-E1

v1

(MeV)γE100 200 300 400 500 600 700 800 900 1000

Inte

nsity

Generated using diamondradiator.Cover full range beam energy.Understood but complexpolarisation energy dependence.

[022,044...] primary contributions.Other vectors angled to not overlap with region.http://nuclear.gla.ac.uk/ kl/GlueX/cbremscans/scan.gif

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Coherent Bremsstrahlung Fit

Currently widely used in most labs.Pros:Information provided by the photon tagger.Polarisation over whole tagged photon energy range.Cons:Very sensitive to orientation of diamond lattice.Indirect measurement.Requires runs with amorphous radiator.Parameters can vary with the same χ2; giving an uncertainty onthe polarisation of about 5%.

(MeV)γE400 500 600 700 800 900 1000

Coh

eren

t Enh

ance

men

t

1.0

1.2

1.4

1.6

1.8

2.0

2.2022

044

Irθ

rφ

θ

φ

γE400 500 600 700 800 900 1000

Phot

on P

olar

isat

ion

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Coherent Bremsstrahlung Fit

Currently widely used in most labs.

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Nuclear Physics Reaction

Examples:Coherent π0 production off spin 0 nucleus (4He,12 C ,208 Pb)ρ meson production.π0 production.Pros:Can use standard experimental detectors.Direct continuous post collimation measurement.Cons:Precise measurement previously made.Inherit systematic uncertainty.Essential to confidently separate background channels.Only valid for specific targets or secondary target needs to beadded.

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Pair and Triplet Production

Pros:Electromagnetic processes described precisely by theory.Direct continuous post collimation measurement.No significant background reactions.Cons:Low count rates.Requires designated additional detector.Lower energy coverage

Pair and Triplet Production

200 400 600 800 100012001400160018002000 (MeV)γE

2−10

1−10

1

10

210

(ba

rns)

σ

Ta PairTa TripletBe PairBe Triplet

[NIST Database]

Pair ProductionPhoton Conversion in nuclearfield.γ + N → e+ + e− + NHigher reaction cross section.Lower analysing power.

Triplet ProductionPhoton Conversion in electronfield.γ + e−atomic → e+ + e− + e−recoilLower reaction cross section.Higher analysing power.

Pair and Triplet Production

[M. Dugger et. al. NIM 867 (2017)]

Pair ProductionPhoton Conversion in nuclearfield.γ + N → e+ + e− + NHigher reaction cross section.Lower analysing power.

Triplet ProductionPhoton Conversion in electronfield.γ + e−atomic → e+ + e− + e−recoilLower reaction cross section.Higher analysing power.

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Triplet Polarimeter - GlueX

Systematic uncertainty estimatedat 1.5%Accumulate over beamtime toget enough statistics for binningpolarisation by photon energy.

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Prototype Pair Polarimeter

γ + N → e+ + e− + N0.1→ 1.5 GeV tagged photonbeam.Pairs converted in Tantalum foil.Separated from beamspot bydipole field.

Two Timepix3 detectors.Scintillation detectors formtrigger.Expected systematic error of< 2%.20 minutes of running underMainz conditions.

Ta Convertor

TPix2

TPix1

Trig2

Trig1

Magnet e−

e+

Prototype Pair Polarimeter

Tests - May - 2019

Location of the pair polarimeterfor tests.

e−

Radiator

Electron Beam Dump

CollimatorTarget

PID

Recoil Polarimeter

CB

TAPS

VETO

Photon Beam Dump

Wall

Pair PolarimeterPair Spectrometer

Tests - May - 2019

0 50 100 150 200 2500

50

100

150

200

250

tpx1Entries 6467905

Mean x 145.1

Mean y 168.5

Std Dev x 70.86

Std Dev y 44.17

Integral 1

Skewness x 0.2953−

Skewness y 0.7797−

Kurtosis x 1.021−

Kurtosis y 1.283

0 0 0

0 1 0

0 0 0

0.05

0.1

0.15

0.2

0.25

3−10×

tpx1Entries 6467905

Mean x 145.1

Mean y 168.5

Std Dev x 70.86

Std Dev y 44.17

Integral 1

Skewness x 0.2953−

Skewness y 0.7797−

Kurtosis x 1.021−

Kurtosis y 1.283

0 0 0

0 1 0

0 0 0

0 50 100 150 200 2500

50

100

150

200

250

tpx1Entries 1.517116e+07

Mean x 145.1

Mean y 168.1

Std Dev x 71.24

Std Dev y 44.02

Integral 1

Skewness x 0.2924−

Skewness y 0.7725−

Kurtosis x 1.035−

Kurtosis y 1.282

0 0 0

0 1 0

0 0 0

0.05

0.1

0.15

0.2

0.25

3−10×

tpx1Entries 1.517116e+07

Mean x 145.1

Mean y 168.1

Std Dev x 71.24

Std Dev y 44.02

Integral 1

Skewness x 0.2924−

Skewness y 0.7725−

Kurtosis x 1.035−

Kurtosis y 1.282

0 0 0

0 1 0

0 0 0

0 50 100 150 200 2500

50

100

150

200

250

Asymmetry_tpx1-tpx1

Entries 17

Mean x 98.9

Mean y 129.3−

Std Dev x 134.1

Std Dev y 288.5

Integral 17.46−

Skewness x 0.6148

Skewness y 2.072−

Kurtosis x 2.114−

Kurtosis y 6.29−

0 0 0

0 17− 0

0 0 0

0.05−

0.04−

0.03−

0.02−

0.01−

0

0.01

0.02

0.03

0.04

0.05

Asymmetry_tpx1-tpx1

Entries 17

Mean x 98.9

Mean y 129.3−

Std Dev x 134.1

Std Dev y 288.5

Integral 17.46−

Skewness x 0.6148

Skewness y 2.072−

Kurtosis x 2.114−

Kurtosis y 6.29−

0 0 0

0 17− 0

0 0 0

0 50 100 150 200 2500

50

100

150

200

250

para1Entries 9101080

Mean x 157.6

Mean y 127.4

Std Dev x 70.96

Std Dev y 23.8

Integral 1

Skewness x 0.4944−

Skewness y 0.07293

Kurtosis x 0.8856−

Kurtosis y 4.985

0 0 0

0 0 0

0 0 0

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

para1Entries 9101080

Mean x 157.6

Mean y 127.4

Std Dev x 70.96

Std Dev y 23.8

Integral 1

Skewness x 0.4944−

Skewness y 0.07293

Kurtosis x 0.8856−

Kurtosis y 4.985

0 0 0

0 0 0

0 0 0

0 50 100 150 200 2500

50

100

150

200

250

perp1Entries 9082553

Mean x 157.7

Mean y 127.5

Std Dev x 70.92

Std Dev y 24.26

Integral 1

Skewness x 0.4968−

Skewness y 0.0629

Kurtosis x 0.8791−

Kurtosis y 4.42

0 0 0

0 1 0

0 0 0

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

perp1Entries 9082553

Mean x 157.7

Mean y 127.5

Std Dev x 70.92

Std Dev y 24.26

Integral 1

Skewness x 0.4968−

Skewness y 0.0629

Kurtosis x 0.8791−

Kurtosis y 4.42

0 0 0

0 1 0

0 0 0

0 50 100 150 200 2500

50

100

150

200

250

Asymmetry_para1-perp1

Entries 154

Mean x 86.44

Mean y 123.2

Std Dev x 56.99

Std Dev y 29.32

Integral 154.2−

Skewness x 0.1171

Skewness y 3.546−

Kurtosis x 1.223−

Kurtosis y 71.41−

0 0 0

0 154− 0

0 0 0

0.1−

0.08−

0.06−

0.04−

0.02−

0

0.02

0.04

0.06

0.08

0.1

Asymmetry_para1-perp1

Entries 154

Mean x 86.44

Mean y 123.2

Std Dev x 56.99

Std Dev y 29.32

Integral 154.2−

Skewness x 0.1171

Skewness y 3.546−

Kurtosis x 1.223−

Kurtosis y 71.41−

0 0 0

0 154− 0

0 0 0

Troubles with timing

Prototype Pair Polarimeter - Simulation

0 50 100 150 200 250 300 350 400Electron Energy

15000

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55000

60000

Cou

nts

Polarisation Extraction

6− 4− 2− 0 2 4 6

6−

4−

2−

0

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4

6

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6− 4− 2− 0 2 4 6

6−

4−

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6− 4− 2− 0 2 4 6

6−

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6− 4− 2− 0 2 4 6

6−

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Polarisation Extraction

0→0.25→0.5→0.75→1 degree of polarisationyDiff

Entries 1650255

Mean 0.00146

Std Dev 1.323

Underflow 0

Overflow 0

Integral 1.65e+06

Skewness 0.005735

Kurtosis 2.277

6− 4− 2− 0 2 4 60

2000

4000

6000

8000

10000

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yDiffEntries 1650255

Mean 0.00146

Std Dev 1.323

Underflow 0

Overflow 0

Integral 1.65e+06

Skewness 0.005735

Kurtosis 2.277

yDiffEntries 1651679

Mean 0.0008885

Std Dev 1.34

Underflow 0

Overflow 0

Integral 1.652e+06

Skewness 0.002614

Kurtosis 2.139

6− 4− 2− 0 2 4 60

2000

4000

6000

8000

10000

12000

14000

16000

18000

yDiffEntries 1651679

Mean 0.0008885

Std Dev 1.34

Underflow 0

Overflow 0

Integral 1.652e+06

Skewness 0.002614

Kurtosis 2.139

yDiffEntries 1652318

Mean 0.0006896

Std Dev 1.357

Underflow 0

Overflow 0

Integral 1.652e+06

Skewness 0.001678

Kurtosis 2.005

6− 4− 2− 0 2 4 60

2000

4000

6000

8000

10000

12000

14000

16000

18000

yDiffEntries 1652318

Mean 0.0006896

Std Dev 1.357

Underflow 0

Overflow 0

Integral 1.652e+06

Skewness 0.001678

Kurtosis 2.005

yDiffEntries 1653380

Mean 0.0007004

Std Dev 1.375

Underflow 0

Overflow 0

Integral 1.653e+06

Skewness 0.002158

Kurtosis 1.879

6− 4− 2− 0 2 4 60

2000

4000

6000

8000

10000

12000

14000

16000

yDiffEntries 1653380

Mean 0.0007004

Std Dev 1.375

Underflow 0

Overflow 0

Integral 1.653e+06

Skewness 0.002158

Kurtosis 1.879

yDiffEntries 1654162

Mean 0.0006502

Std Dev 1.392

Underflow 0

Overflow 0

Integral 1.654e+06

Skewness 0.001783

Kurtosis 1.752

6− 4− 2− 0 2 4 60

2000

4000

6000

8000

10000

12000

14000

16000

yDiffEntries 1654162

Mean 0.0006502

Std Dev 1.392

Underflow 0

Overflow 0

Integral 1.654e+06

Skewness 0.001783

Kurtosis 1.752

6− 4− 2− 0 2 4 6

6−

4−

2−

0

2

4

6

yDiffEntries 873990

Mean x 0.4607

Mean y 0.0003787

Std Dev x 1.202

Std Dev y 1.323

Integral 8.74e+05

Skewness x 0.4089−

Skewness y 0.002773

Kurtosis x 2.263

Kurtosis y 2.288

0 0 0

0 873990 0

0 0 0

0

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1000

1500

2000

2500

3000

yDiffEntries 873990

Mean x 0.4607

Mean y 0.0003787

Std Dev x 1.202

Std Dev y 1.323

Integral 8.74e+05

Skewness x 0.4089−

Skewness y 0.002773

Kurtosis x 2.263

Kurtosis y 2.288

0 0 0

0 873990 0

0 0 0

6− 4− 2− 0 2 4 6

6−

4−

2−

0

2

4

6

yDiffEntries 1040401

Mean x 0.4642

Mean y 0.001355

Std Dev x 1.19

Std Dev y 1.339

Integral 1.04e+06

Skewness x 0.4409−

Skewness y 0.0031

Kurtosis x 2.436

Kurtosis y 2.145

0 0 0

0 1040401 0

0 0 0

0

500

1000

1500

2000

2500

3000

3500

yDiffEntries 1040401

Mean x 0.4642

Mean y 0.001355

Std Dev x 1.19

Std Dev y 1.339

Integral 1.04e+06

Skewness x 0.4409−

Skewness y 0.0031

Kurtosis x 2.436

Kurtosis y 2.145

0 0 0

0 1040401 0

0 0 0

6− 4− 2− 0 2 4 6

6−

4−

2−

0

2

4

6

yDiffEntries 1008168

Mean x 0.469

Mean y 0.001068

Std Dev x 1.174

Std Dev y 1.356

Integral 1.008e+06

Skewness x 0.4501−

Skewness y 0.0007782−

Kurtosis x 2.546

Kurtosis y 2.008

0 0 0

0 1008168 0

0 0 0

0

500

1000

1500

2000

2500

3000

3500

yDiffEntries 1008168

Mean x 0.469

Mean y 0.001068

Std Dev x 1.174

Std Dev y 1.356

Integral 1.008e+06

Skewness x 0.4501−

Skewness y 0.0007782−

Kurtosis x 2.546

Kurtosis y 2.008

0 0 0

0 1008168 0

0 0 0

6− 4− 2− 0 2 4 6

6−

4−

2−

0

2

4

6

yDiffEntries 959027

Mean x 0.4749

Mean y 0.0004641−

Std Dev x 1.157

Std Dev y 1.375

Integral 9.59e+05

Skewness x 0.4538−

Skewness y 0.001215−

Kurtosis x 2.665

Kurtosis y 1.89

0 0 0

0 959027 0

0 0 0

0

500

1000

1500

2000

2500

3000

yDiffEntries 959027

Mean x 0.4749

Mean y 0.0004641−

Std Dev x 1.157

Std Dev y 1.375

Integral 9.59e+05

Skewness x 0.4538−

Skewness y 0.001215−

Kurtosis x 2.665

Kurtosis y 1.89

0 0 0

0 959027 0

0 0 0

6− 4− 2− 0 2 4 6

6−

4−

2−

0

2

4

6

yDiffEntries 1008781

Mean x 0.4781

Mean y 0.001724

Std Dev x 1.147

Std Dev y 1.392

Integral 1.009e+06

Skewness x 0.4804−

Skewness y 0.00874

Kurtosis x 2.85

Kurtosis y 1.758

0 0 0

0 1008781 0

0 0 0

0

500

1000

1500

2000

2500

3000

3500

yDiffEntries 1008781

Mean x 0.4781

Mean y 0.001724

Std Dev x 1.147

Std Dev y 1.392

Integral 1.009e+06

Skewness x 0.4804−

Skewness y 0.00874

Kurtosis x 2.85

Kurtosis y 1.758

0 0 0

0 1008781 0

0 0 0

Polarisation Extraction

0.0 0.2 0.4 0.6 0.8 1.0Target

0.015

0.010

0.005

0.000

0.005

Resid

ual

Regression

0.0 0.2 0.4 0.6 0.8 1.0Target

0.0

0.2

0.4

0.6

0.8

1.0

Pred

ictio

n

Regression

0 100 200 300 400 500Y-Position

30

20

10

0

10

20

Fit G

radi

ent

Linear regression of histogram bins contents.

Fit line to the change in histogram bin fraction with polarisation.Less than 0.5% error, would improve additional simulations.

Outline

1 Motivation2 Generation of Coherent Bremsstrahlung3 Coherent Bremsstrahlung Fit4 Nuclear Physics Reaction5 Pair and Triplet Production6 Triplet Polarimeter - GlueX7 Prototype Pair Polarimeter8 Coherent Bremsstrahlung of the Future

Coherent Bremsstrahlung of the Future

Running at Bonn, Mainz and J-Lab for nowSpeculative facilities:

DAΦNE

ILC (International Linear Collider) - 125 GeV real photons

Summary

Current methods for determining the degree of polarisationare no longer good enough.

GlueX has proved the effectiveness of a polarimeter.

A pair polarimeter would increase allow measurements atMainz rates.

END