Threshold production/Compton scattering on the deuteron Bruno - - PowerPoint PPT Presentation

Introduction Experiment Analysis Summary

Threshold π− production/Compton scattering on the deuteron

Bruno Strandberg

The University Of Glasgow Nuclear Physics Group June 6, 2016

Introduction Experiment Analysis Summary

Outline

1

Introduction

2

Experiment Experimental setup Event counting

3

Analysis Backgrounds Signals Expected results

4

Summary

Introduction Experiment Analysis Summary

Introduction

Why measure γ + 2H → π− + 2p (γ + n → π− + p)?

Introduction Experiment Analysis Summary

Why measure γ + 2H → π− + 2p (γ + n → π− + p)? Provides a test for various low-energy QCD models.

Dispersion Theory Effective Field Theories SAID/MAID models

Introduction Experiment Analysis Summary

Why measure γ + 2H → π− + 2p (γ + n → π− + p)? Provides a test for various low-energy QCD models.

Dispersion Theory Effective Field Theories SAID/MAID models

Available cross-section data points below Eγ = 200 MeV [1]:

π0: 1524 π+: 92 π−: 51

Introduction Experiment Analysis Summary

Why measure γ + 2H → π− + 2p (γ + n → π− + p)? Provides a test for various low-energy QCD models.

Dispersion Theory Effective Field Theories SAID/MAID models

Available cross-section data points below Eγ = 200 MeV [1]:

π0: 1524 π+: 92 π−: 51

No π− data below Eγ = 158 MeV. Last known π− measurement in 1994 by Liu (PhD thesis, unpublished).

Introduction Experiment Analysis Summary

Why measure γ + 2H → γ′ + 2H?

Introduction Experiment Analysis Summary

Why measure γ + 2H → γ′ + 2H? Access neutron polarisabilities.

Introduction Experiment Analysis Summary

Why measure γ + 2H → γ′ + 2H? Access neutron polarisabilities. Test for HBχPT.

Introduction Experiment Analysis Summary

Why measure γ + 2H → γ′ + 2H? Access neutron polarisabilities. Test for HBχPT. No data close above pion threshold.

Introduction Experiment Analysis Summary

Experiment - setup

Introduction Experiment Analysis Summary

The experiment was performed at Maxlab in Lund, Sweden.

Introduction Experiment Analysis Summary

The experiment was performed at Maxlab in Lund, Sweden. Mainly a synchrotron radiation facility. For nuclear physics: electron beam with Ee = 190 MeV

Introduction Experiment Analysis Summary

The experiment was performed at Maxlab in Lund, Sweden. Mainly a synchrotron radiation facility. For nuclear physics: electron beam with Ee = 190 MeV Create tagged Bremsstrahlung photon beam from electron beam, Eγ from 140 to 160 MeV.

Tagging magnet Incoming e− Radiator Bremsstrahlung γ Experimental hall Collimator Post-Bremsstrahlung e−

Counter #1 Counter #3 Counter #5 ...

Focal Plane Detector

Counter #2 Counter #4 Counter #6 ... Ch0 Ch1 Ch2 Ch3 Ch4 ...

Introduction Experiment Analysis Summary

BUNI

222 mm 96 mm 761.7 mm 559 mm 150 mm 381mm

CATS

240 mm 210 mm 703 mm 635 mm 138 mm 297 mm

DIANA

372 mm 115 mm 560 mm 510 mm 200 mm 822 mm

z-axis

60➦ 150➦ 120➦

γ

Figure : Floor plan of the experiment at Maxlab in Lund, Sweden.

Introduction Experiment Analysis Summary

Figure : Experimental hall at Maxlab in Lund, Sweden.

Introduction Experiment Analysis Summary

Experiment - event counting

Introduction Experiment Analysis Summary

Reaction γ + 2H → π− + 2p, pion produced on the neutron.

Incoming γ p p π− Liquid deuterium target 150 mm 68 mm

Introduction Experiment Analysis Summary

Reaction γ + 2H → π− + 2p, pion produced on the neutron.

Incoming γ p p π− n n γ Liquid deuterium target 150 mm 68 mm

Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.2 0.4 0.6 0.8 1

capture simulation

• π

Radiative capture reaction π− + 2H → γ + 2n, pion captured on the proton. Identify pions through counting radiative capture photons.

Introduction Experiment Analysis Summary

Reaction γ + 2H → π− + 2p, pion produced on the neutron.

Incoming γ p p π− n n γ Liquid deuterium target 150 mm 68 mm

Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.2 0.4 0.6 0.8 1

capture simulation

• π

Radiative capture reaction π− + 2H → γ + 2n, pion captured on the proton. Identify pions through counting radiative capture photons. Assumption: radiative photons emitted isotropically, effectively we do 3 simultaneous σ measurements.

Introduction Experiment Analysis Summary

Competing scenarios to radiative capture π− + 2H → γ + 2n? Incoming γ p p π− Liquid deuterium target 150 mm 68 mm

Introduction Experiment Analysis Summary

Competing scenarios to radiative capture π− + 2H → γ + 2n? Escape from target volume - Geant4 simulation. Incoming γ p p π− Liquid deuterium target 150 mm 68 mm

Introduction Experiment Analysis Summary

Competing scenarios to radiative capture π− + 2H → γ + 2n? Escape from target volume - Geant4 simulation. Decay - Geant4 simulation. Incoming γ p p π− µ− ¯ νµ Liquid deuterium target 150 mm 68 mm

Introduction Experiment Analysis Summary

Competing scenarios to radiative capture π− + 2H → γ + 2n? Escape from target volume - Geant4 simulation. Decay - Geant4 simulation. Non-rad capture π− + 2H → 2n - Branching ratio known

π−+2H→2n π−+2H→γ2n = 2.83 ± 0.04 [2]

Incoming γ p p π− n n Liquid deuterium target 150 mm 68 mm

Introduction Experiment Analysis Summary

Competing scenarios to radiative capture π− + 2H → γ + 2n? Escape from target volume - Geant4 simulation. Decay - Geant4 simulation. Non-rad capture π− + 2H → 2n - Branching ratio known

π−+2H→2n π−+2H→γ2n = 2.83 ± 0.04 [2]

Other scenarios ∼< 1% [3, 4, 5] Incoming γ p p π− Liquid deuterium target 150 mm 68 mm

Introduction Experiment Analysis Summary

The Compton events γ + 2H → γ′ + 2H′ are identified through Eγ − Eγ′ = 0.

[MeV]

γ

• E

' γ

E

14 − 12 − 10 − 8 − 6 − 4 − 2 − 2 4

Events

0.2 0.4 0.6 0.8 1

Compton scattering simulation

Introduction Experiment Analysis Summary

The Compton events γ + 2H → γ′ + 2H′ are identified through Eγ − Eγ′ = 0.

[MeV]

γ

• E

' γ

E

14 − 12 − 10 − 8 − 6 − 4 − 2 − 2 4

Events

0.2 0.4 0.6 0.8 1

Compton scattering simulation

Note the difference compared to π− measurement:

Introduction Experiment Analysis Summary

The Compton events γ + 2H → γ′ + 2H′ are identified through Eγ − Eγ′ = 0.

[MeV]

γ

• E

' γ

E

14 − 12 − 10 − 8 − 6 − 4 − 2 − 2 4

Events

0.2 0.4 0.6 0.8 1

Compton scattering simulation

Note the difference compared to π− measurement: For π− we measure σ VS For Compton we measure dσ

dΩ points.

Introduction Experiment Analysis Summary

Analysis - backgrounds

Neutron background channels:

Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

2n γ → H

2

• π

Signal and background contributions

Introduction Experiment Analysis Summary

Neutron background channels:

1 Non-rad. capture π− + 2H → 2n, 2.83 × σγ2n (Geant4) Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

2n γ → H

2

• π

2n → H

2

• π

Signal and background contributions

Introduction Experiment Analysis Summary

Neutron background channels:

1 Non-rad. capture π− + 2H → 2n, 2.83 × σγ2n (Geant4) 2 Photodisinteg. γ + 2H → np, σnp ∼ σπ−2p (Geant4, [6]) Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

2n γ → H

2

• π

2n → H

2

• π

np → H

2

γ

Signal and background contributions

Introduction Experiment Analysis Summary

Neutron background channels:

1 Non-rad. capture π− + 2H → 2n, 2.83 × σγ2n (Geant4) 2 Photodisinteg. γ + 2H → np, σnp ∼ σπ−2p (Geant4, [6]) Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

2n γ → H

2

• π

Kapton bkg

Signal and background contributions

Other background channels:

1 Kapton container background, measured (dummy target run).

Introduction Experiment Analysis Summary

Neutron background channels:

1 Non-rad. capture π− + 2H → 2n, 2.83 × σγ2n (Geant4) 2 Photodisinteg. γ + 2H → np, σnp ∼ σπ−2p (Geant4, [6]) Detected Energy [MeV]

50 60 70 80 90 100 110 120 130 140

Events

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

2n γ → H

2

• π

Kapton bkg bkg π

Signal and background contributions

Other background channels:

1 Kapton container background, measured (dummy target run). 2 Pi0 single photon background, σπ0np < σπ−2p (Geant4).

Introduction Experiment Analysis Summary

Analysis - signals

Introduction Experiment Analysis Summary

π− production signal by incident Eγ (prelim)

Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 Events 100 200 300 400 500 600 700

No neutron bkg With neutron bkg = 140.82

gamma

E Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 Events 100 200 300 400 500 600 700 No neutron bkg With neutron bkg = 148.69

gamma

E Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 Events 100 200 300 400 500 600 700

No neutron bkg With neutron bkg = 156.55

gamma

E

Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 100 200 300 400 500 600 700

No neutron bkg With neutron bkg = 143.45

gamma

E Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 100 200 300 400 500 600 700 No neutron bkg With neutron bkg = 151.31

gamma

E Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 100 200 300 400 500 600 700

No neutron bkg With neutron bkg = 158.85

gamma

E

Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 100 200 300 400 500 600 700

No neutron bkg With neutron bkg = 146.07

gamma

E Detected Energy [MeV] 50 60 70 80 90 100 110 120 130 140 100 200 300 400 500 600 700 No neutron bkg With neutron bkg = 153.93

gamma

E

Introduction Experiment Analysis Summary

Compton signal by incident Eγ at θ = 60◦ (prelim)

Missing Energy [MeV]

20 − 15 − 10 − 5 − 5 10 15 20

Count

10 − 10 20 30 40 50

= 142.14

gamma

E Missing Energy [MeV]

20 − 15 − 10 − 5 − 5 10 15 20

Count

10 − 10 20 30 40 50 60

= 147.38

gamma

E Missing Energy [MeV]

20 − 15 − 10 − 5 − 5 10 15 20

Count

10 − 10 20 30 40

= 152.62

gamma

E Missing Energy [MeV]

20 − 15 − 10 − 5 − 5 10 15 20

Count

10 20 30 40

= 157.54

gamma

E

Introduction Experiment Analysis Summary

Analysis - π− expected results

Introduction Experiment Analysis Summary

π− on deuteron: σ at eight Eγ values from 140 to 160 MeV in ∼ 2 MeV bins.

[MeV]

_lab γ

E

140 150 160 170 180 190 200

b] µ [ σ

20 40 60 80 100 120 140 MAID SAID Liu 94' White 60' Salomon 84' Rossi 73' Bagheri 88' Wang 92' Projections'

2p reaction

• π

→ H

2

γ p predictions and data [1]

• π

n -> γ

Introduction Experiment Analysis Summary

π− on deuteron: σ at eight Eγ values from 140 to 160 MeV in ∼ 2 MeV bins.

[MeV]

_lab γ

E

140 150 160 170 180 190 200

b] µ [ σ

20 40 60 80 100 120 140 MAID SAID Liu 94' White 60' Salomon 84' Rossi 73' Bagheri 88' Wang 92' Projections'

2p reaction

• π

→ H

2

γ p predictions and data [1]

• π

n -> γ

Shown signals include roughly 50-60% of data, with all data statistical uncertainty < 5%.

Introduction Experiment Analysis Summary

π− on deuteron: σ at eight Eγ values from 140 to 160 MeV in ∼ 2 MeV bins.

[MeV]

_lab γ

E

140 150 160 170 180 190 200

b] µ [ σ

20 40 60 80 100 120 140 MAID SAID Liu 94' White 60' Salomon 84' Rossi 73' Bagheri 88' Wang 92' Projections'

2p reaction

• π

→ H

2

γ p predictions and data [1]

• π

n -> γ

Shown signals include roughly 50-60% of data, with all data statistical uncertainty < 5%. This will be first good statistics threshold data.

Introduction Experiment Analysis Summary

Analysis - Compton expected results

Introduction Experiment Analysis Summary

Analysis - Compton expected results

Compton on deuteron: differential cross-section dσ/dΩ values in 4 energy bins at 2(3?) angles.

[MeV]

_lab γ

E

142 144 146 148 150 152 154 156 158

[Deg]

lab

θ

20 40 60 80 100 120 140 160 180

? ? expected results grid Ω /d σ Compton d

Introduction Experiment Analysis Summary

Analysis - Compton expected results

Compton on deuteron: differential cross-section dσ/dΩ values in 4 energy bins at 2(3?) angles.

[MeV]

_lab γ

E

142 144 146 148 150 152 154 156 158

[Deg]

lab

θ

20 40 60 80 100 120 140 160 180

? ? expected results grid Ω /d σ Compton d

Shown signals include roughly 50-60% of data, with all data statistical uncertainty ∼ 10%.

Introduction Experiment Analysis Summary

Analysis - Compton expected results

Compton on deuteron: differential cross-section dσ/dΩ values in 4 energy bins at 2(3?) angles.

[MeV]

_lab γ

E

142 144 146 148 150 152 154 156 158

[Deg]

lab

θ

20 40 60 80 100 120 140 160 180

? ? expected results grid Ω /d σ Compton d

Shown signals include roughly 50-60% of data, with all data statistical uncertainty ∼ 10%. This will be first Compton measurement in above threshold region.

Introduction Experiment Analysis Summary

Summary

Introduction Experiment Analysis Summary

Summary

π−/Compton on deuteron measurement motivation: Provide test for low-energy QCD models. No previous measurement.

Introduction Experiment Analysis Summary

Summary

π−/Compton on deuteron measurement motivation: Provide test for low-energy QCD models. No previous measurement. Experiment and analysis: Analysis components and procedures well understood. Preliminary results show promise.

Introduction Experiment Analysis Summary

Summary

π−/Compton on deuteron measurement motivation: Provide test for low-energy QCD models. No previous measurement. Experiment and analysis: Analysis components and procedures well understood. Preliminary results show promise. Expected results: π− σ on deuteron: value at 8 energies. Compton dσ/dΩ on deuteron: 5(7?) points.

Introduction Experiment Analysis Summary

Summary

π−/Compton on deuteron measurement motivation: Provide test for low-energy QCD models. No previous measurement. Experiment and analysis: Analysis components and procedures well understood. Preliminary results show promise. Expected results: π− σ on deuteron: value at 8 energies. Compton dσ/dΩ on deuteron: 5(7?) points. I would like to thank the MAXTagg collaboration and the MESONS2016 conference. Thank you for listening!

References I

http://gwdac.phys.gwu.edu V.L. Highland et. al., Branching Ratios For Stopped Pions In Deuterium, 1981. D.W. Joseph, Electron Pair Production in π− + d Capture, 1960.

• S. Tripathi et al. Double radiative pion capture on hydrogen

and deuterium and the nucleons pion cloud, 2007.

• R. MacDonald et al. Charge Exchange of Stopped π− in

Deuterium: Experiment and Theory, 1977. D.A. Jenkins et al. 2H(γ, p)n cross section between 20 and 440 MeV, 1994.