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 Introduction 1 Experiment 2 Experimental setup Event counting Analysis 3 Backgrounds Signals Expected results Summary 4

Introduction Experiment Analysis Summary Introduction Why measure γ + 2 H → π − + 2p ( γ + n → π − + p )?

Introduction Experiment Analysis Summary Why measure γ + 2 H → 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 + 2 H → 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 E γ = 200 MeV [1]: π 0 : 1524 π + : 92 π − : 51

Introduction Experiment Analysis Summary Why measure γ + 2 H → 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 E γ = 200 MeV [1]: π 0 : 1524 π + : 92 π − : 51 No π − data below E γ = 158 MeV . Last known π − measurement in 1994 by Liu (PhD thesis, unpublished).

Introduction Experiment Analysis Summary Why measure γ + 2 H → γ ′ + 2 H ?

Introduction Experiment Analysis Summary Why measure γ + 2 H → γ ′ + 2 H ? Access neutron polarisabilities.

Introduction Experiment Analysis Summary Why measure γ + 2 H → γ ′ + 2 H ? Access neutron polarisabilities. Test for HB χ PT.

Introduction Experiment Analysis Summary Why measure γ + 2 H → γ ′ + 2 H ? Access neutron polarisabilities. Test for HB χ PT. 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 E e = 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 E e = 190 MeV Create tagged Bremsstrahlung photon beam from electron beam, E γ from 140 to 160 MeV. Experimental hall Collimator Bremsstrahlung γ Tagging magnet Post-Bremsstrahlung e − Radiator Incoming e − ... Counter #6 Counter #4 Counter #2 ... Counter #5 Counter #3 Counter #1 ... Ch4 Ch3 Ch2 Ch1 Ch0 Focal Plane Detector

Introduction Experiment Analysis Summary 761.7 mm BUNI 222 mm 559 mm 150 mm 381mm 96 mm γ z-axis 120 ➦ 210 mm 150 ➦ 60 ➦ 822 mm 297 mm 372 mm 200 mm 138 mm 635 mm 240 mm 115 mm DIANA 560 mm CATS 510 mm 703 mm 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 + 2 H → π − + 2p , pion produced on the neutron. Liquid deuterium target p Incoming γ π − 68 mm p 150 mm

Introduction Experiment Analysis Summary Reaction γ + 2 H → π − + 2p , pion produced on the neutron. π - capture simulation Liquid deuterium target 1 n n p 0.8 Incoming γ π − Events 0.6 68 mm 0.4 p 0.2 γ 150 mm 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV] Radiative capture reaction π − + 2 H → γ + 2n , pion captured on the proton. Identify pions through counting radiative capture photons .

Introduction Experiment Analysis Summary Reaction γ + 2 H → π − + 2p , pion produced on the neutron. π - capture simulation Liquid deuterium target 1 n n p 0.8 Incoming γ π − Events 0.6 68 mm 0.4 p 0.2 γ 150 mm 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV] Radiative capture reaction π − + 2 H → 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 − + 2 H → γ + 2n ? Liquid deuterium target p Incoming γ π − 68 mm p 150 mm

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

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

Introduction Experiment Analysis Summary Competing scenarios to radiative capture π − + 2 H → γ + 2n ? Escape from target volume - Geant4 simulation . Decay - Geant4 simulation . Non-rad capture π − + 2 H → 2n - Branching ratio known π − + 2 H → 2n π − + 2 H → γ 2n = 2 . 83 ± 0 . 04 [2] Liquid deuterium target n p Incoming γ π − 68 mm n p 150 mm

Introduction Experiment Analysis Summary Competing scenarios to radiative capture π − + 2 H → γ + 2n ? Escape from target volume - Geant4 simulation . Decay - Geant4 simulation . Non-rad capture π − + 2 H → 2n - Branching ratio known π − + 2 H → 2n π − + 2 H → γ 2n = 2 . 83 ± 0 . 04 [2] Other scenarios ∼ < 1% [3, 4, 5] Liquid deuterium target p Incoming γ π − 68 mm p 150 mm

Introduction Experiment Analysis Summary The Compton events γ + 2 H → γ ′ + 2 H ′ are identified through E γ − E γ ′ = 0. Compton scattering simulation 1 0.8 Events 0.6 0.4 0.2 0 − − − − − − − 14 12 10 8 6 4 2 0 2 4 E - E [MeV] γ γ '

Introduction Experiment Analysis Summary The Compton events γ + 2 H → γ ′ + 2 H ′ are identified through E γ − E γ ′ = 0. Compton scattering simulation 1 0.8 Events 0.6 0.4 0.2 0 − − − − − − − 14 12 10 8 6 4 2 0 2 4 E - E [MeV] γ γ ' Note the difference compared to π − measurement:

Introduction Experiment Analysis Summary The Compton events γ + 2 H → γ ′ + 2 H ′ are identified through E γ − E γ ′ = 0. Compton scattering simulation 1 0.8 Events 0.6 0.4 0.2 0 − − − − − − − 14 12 10 8 6 4 2 0 2 4 E - E [MeV] γ γ ' Note the difference compared to π − measurement: For π − we measure σ VS For Compton we measure d σ d Ω points.

Introduction Experiment Analysis Summary Analysis - backgrounds Neutron background channels: Signal and background contributions 0.08 0.07 0.06 0.05 Events 0.04 0.03 0.02 π - 2 → γ H 2n 0.01 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV]

Introduction Experiment Analysis Summary Neutron background channels: 1 Non-rad. capture π − + 2 H → 2n , 2 . 83 × σ γ 2n (Geant4) Signal and background contributions 0.08 0.07 0.06 0.05 Events 0.04 0.03 0.02 π - 2 → γ H 2n 0.01 π - 2 → H 2n 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV]

Introduction Experiment Analysis Summary Neutron background channels: 1 Non-rad. capture π − + 2 H → 2n , 2 . 83 × σ γ 2n (Geant4) 2 Photodisinteg. γ + 2 H → np , σ np ∼ σ π − 2p (Geant4, [6]) Signal and background contributions 0.08 0.07 0.06 0.05 Events 0.04 0.03 γ 2 → H np 0.02 π - 2 → γ H 2n 0.01 π - 2 → H 2n 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV]

Introduction Experiment Analysis Summary Neutron background channels: 1 Non-rad. capture π − + 2 H → 2n , 2 . 83 × σ γ 2n (Geant4) 2 Photodisinteg. γ + 2 H → np , σ np ∼ σ π − 2p (Geant4, [6]) Signal and background contributions 0.08 0.07 0.06 0.05 Events 0.04 0.03 0.02 π - 2 → γ H 2n 0.01 Kapton bkg 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV] Other background channels: 1 Kapton container background, measured (dummy target run).

Introduction Experiment Analysis Summary Neutron background channels: 1 Non-rad. capture π − + 2 H → 2n , 2 . 83 × σ γ 2n (Geant4) 2 Photodisinteg. γ + 2 H → np , σ np ∼ σ π − 2p (Geant4, [6]) Signal and background contributions 0.08 0.07 0.06 0.05 Events 0.04 0.03 π 0 bkg 0.02 π - 2 → γ H 2n 0.01 Kapton bkg 0 50 60 70 80 90 100 110 120 130 140 Detected Energy [MeV] Other background channels: 1 Kapton container background, measured (dummy target run). 2 Pi0 single photon background, σ π 0 np < σ π − 2p (Geant4).

Introduction Experiment Analysis Summary Analysis - signals