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Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle Munich, June 13 th 2011 XIV International Conference on Hadron Spectroscopy 2 Collaboration a Single 0 Photoproduction Double 0 Photoproduction Outline Motivation

  1. Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle Munich, June 13 th 2011 XIV International Conference on Hadron Spectroscopy 2 Collaboration a

  2. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Outline 1 Motivation 2 Single π 0 Photoproduction Status Experiment Results 3 Double π 0 Photoproduction Total Cross Sections Beam-Helicity Asymmetry 4 Conclusions Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  3. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions � Why Photoproduction of π 0 ? ◮ Test modern hadron models by studying nucleon resonances N ( J P N ( J P N ) N ) N ∗ ( J P N ∗ ) � � � π 0 ( L P γ ( L P γ ) π 0 ) ◮ Small coupling of photons to neutral mesons Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  4. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions � Why Photoproduction of π 0 ? ◮ Test modern hadron models by studying nucleon resonances N ( J P N ( J P N ) N ) N ∗ ( J P N ∗ ) � � � π 0 ( L P γ ( L P γ ) π 0 ) ◮ Small coupling of photons to neutral mesons Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  5. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Why on the Neutron? ◮ Isospin amplitudes of the elm. transitions depend on reactions on proton and neutron √ 2( A (0) + A ( − ) ) A ( γ p → π + n ) = √ 2( A (0) − A ( − ) ) A (0) := isoscalar A ( γ n → π − p ) = A ( γ p → π 0 p ) = ( A (+) + A (0) ) A (+) , A ( − ) := isovector A ( γ n → π 0 n ) = ( A (+) − A (0) ) ◮ meson photoproduction from light nuclei, i.e. deuteron ◮ nuclear effects (rescattering of the mesons, FSI, ...) Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  6. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions World π 0 Data γ p → p π o γ n → n π o 2 1.5 E γ [ GeV ] 1 0.5 0 -1 0 1 -1 0 1 cos( Θ π ) SAID Data Base - http://gwdac.phys.gwu.edu/ Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  7. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Former Results - MAMI 1999 x10 2 σ ( π 0 np ) / A 0.5 ● σ ( π 0 d ) / A 3 0.4 σ ( π 0 p ) � 0.3 σ /A [µ b ] 2  σ ( π 0 p ) folded 0.2 500 600 700 800 γ p →π o p 1 γ d →π o np ◮ significant reduction in σ/ A γ d →π o d compared to free proton ◮ can not be explained alone by 0 Fermi motion 200 400 600 800 photon energy [ MeV ] ◮ nuclear effect? FSI? B. Krusche et al., Eur. Phys. J. A 6(1999) 309 Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  8. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Former Results - LNS Sendai 2009 σ ′ ( − 0 . 7 < cos θ ∗ π 0 < 0 . 6) σ ( π 0 np ) ● σ ( π 0 p ) � σ ( π 0 n ) = σ ( π 0 np ) − σ ( π 0 p ) △  0 . 8 ∗ MAID folded ◮ can not be explained alone by Fermi motion ◮ nuclear effect? FSI? H. Shimizu, NNR workshop 2009 Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  9. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Experiment MAinzer MIcrotron, Dec 2007 ◮ Photon beam energies up to ∼ 1 . 4 GeV ◮ Target: ∼ 5 cm LD 2 ◮ Detectors: ◮ Crystal Ball ( CB ): ◮ surrounding the target ◮ Two Arm Photon Spectrometer ( TAPS ): ◮ placed as forward wall ◮ ∼ 4 π steradian Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  10. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Identification of the Reaction Channels Reaction mechanism for π 0 photoproduction on deuterium: π 0 + p ( n )  QF on proton   π 0 + n ( p )  QF on neutron γ + d →  E γ > 500 MeV π 0 + d  Coherent ( 0) − →  Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  11. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Identification of the Reaction Channels Reaction mechanism for π 0 photoproduction on deuterium: π 0 + p ( n )  QF on proton   π 0 + n ( p )  QF on neutron γ + d →  E γ > 500 MeV π 0 + d  Coherent ( 0) − →  Measurements: γ + d → π 0 + p Exclusive on P: γ + d → π 0 + n + Exclusive on N: γ + d → π 0 + ( N ) QF-Inclusive: ≈ Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  12. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions π 0 Total Cross Sections PRELIMINARY 80 σ π 0 ( p) 70 σ π 0 ( n) 60 MAID folded 50 SAID folded b] µ 40 [ σ 30 20 10 0 400 600 800 1000 1200 1400 E [MeV] γ Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  13. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions π 0 Total Cross Sections PRELIMINARY PRELIMINARY 80 140 σ π 0 σ π 0 ( np) ( p) 70 σ π σ π 0 0 ( n) + ( p) 120 σ π 0 ( n) 60 σ π 0 ( np) B. Krusche et al. MAID folded 100 50 MAID folded SAID folded b] b] SAID folded 80 µ µ 40 [ [ σ σ 60 30 40 20 20 10 0 0 400 600 800 1000 1200 1400 400 600 800 1000 1200 1400 E [MeV] E [MeV] γ γ Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  14. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Comparison to Models PRELIMINARY 60 σ π 0 ( p) σ π 0 50 ( n) σ π 0 ( np) 0.8*MAID folded 40 0.8*SAID folded b] MAID and SAID model µ 30 [ scaled down with factor σ 0 . 8 20 10 0 600 700 800 900 1000 110012001300 1400 E [MeV] γ Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  15. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Resonance Contributions Contributions Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  16. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Resonance Contributions D 13 : p,n Contributions Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  17. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Resonance Contributions D 13 : p,n Contributions F 15 : p Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  18. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Resonance Contributions D 13 : p,n Contributions F 15 : p D 15 : n Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  19. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions 2 π 0 Total Cross Sections (M. Oberle et al.) Dominated by sequential decay PRELIMINARY N * (I=1/2) π ∆ (1232) ρ σ π N(938) Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  20. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Resonance Contributions p ( γ, 2 π 0 ) p n ( γ, 2 π 0 ) n ◮ Electromagnetic excitation ◮ Electromagnetic excitation of the F 15 stronger on the of the D 15 stronger on the proton neutron Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  21. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions The Beam-Helicity Asymmetry Helicity h = � S ˆ P = − S , ..., S d σ + − d σ − N + − N − 1 1 I ⊙ (Φ) = d σ + + d σ − = N + + N − P γ P γ Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  22. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Former Results (D. Krambrich, F. Zehr et al.) � Data  ◮ Asymmetry indicates strong Fit to Data sensitivity to reaction mechanisms  Fix and Arenh¨ ovel model ◮ Early results contradicted many  Roca model predictions  BoGa model D. Krambrich, F. Zehr et al., Phys. Rev. Lett. 103 (2009) 052002 Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  23. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Helicity Asymmetries for 2 π 0 (M. Oberle et al.) PRELIMINARY p ( γ, 2 π 0 ) p n ( γ, 2 π 0 ) n p ( γ, 2 π 0 ) p Fermi defolded compared to free p (F.Zehr et al.) Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

  24. Single π 0 Photoproduction Double π 0 Photoproduction Outline Motivation Conclusions Conclusions Single π 0 Photoproduction: ◮ Cross Sections for Single π 0 in good agreement with former results ◮ MAID/SAID overestimate the cross sections by 25% ◮ Reduction can not only be explained by Fermi motion Double π 0 Photoproduction: ◮ Same asymmetries for 2 π 0 on the proton as on the neutron ◮ Model predictions not yet in agreement with results, further input needed ◮ Electromagnetic excitation of the resonances different for proton and neutron. De-excitation of the resonances different for single and double pion production. Single and Double Pion Photoproduction off the Deuteron Manuel Dieterle

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