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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
20000
25000
30000
35000
40000
45000
50000
55000
60000
Cou
nts
Polarisation Extraction
6− 4− 2− 0 2 4 6
6−
4−
2−
0
2
4
6
0
200
400
600
800
1000
1200
6− 4− 2− 0 2 4 6
6−
4−
2−
0
2
4
6
0
200
400
600
800
1000
1200
6− 4− 2− 0 2 4 6
6−
4−
2−
0
2
4
6
0
100
200
300
400
500
600
6− 4− 2− 0 2 4 6
6−
4−
2−
0
2
4
6
0
100
200
300
400
500
600
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
12000
14000
16000
18000
20000
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
500
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